JP7070321B2 - All solid state battery - Google Patents

Description

The present disclosure relates to an all-solid-state battery capable of suppressing an increase in battery internal temperature.

The all-solid-state battery is a battery having a solid electrolyte layer between the positive electrode and the negative electrode, and has an advantage that the safety device can be easily simplified as compared with a liquid-based battery having an electrolytic solution containing a flammable organic solvent. ..

For example, Patent Document 1 and Patent Document 2 disclose an all-solid-state battery having a PTC (Positive Temperature Coefficient) film between a negative electrode active material layer and a negative electrode current collector layer.

Japanese Unexamined Patent Publication No. 2018-116810 Japanese Unexamined Patent Publication No. 2018-014286

In Patent Document 1 and Patent Document 2, by forming a PTC film on a negative electrode current collector, for example, when overcharging occurs, the thermoplastic resin binder in the PTC film expands due to a temperature rise, and electron conduction occurs. By cutting the path, the temperature rise is suppressed. On the other hand, it is preferable to further improve the reliability of the battery.

An object of the present disclosure is to provide an all-solid-state battery capable of suppressing an increase in battery internal temperature.

In order to solve the above problems, the present inventor, as a result of diligent studies, can further suppress an increase in the internal temperature of the battery by cutting the electron conducting path at a temperature lower than the temperature at which the resin binder expands. I found out what I could do.
In the present disclosure, an all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer formed between the positive electrode and the negative electrode, wherein the negative electrode is a negative electrode active material having a lithium storage potential higher than that of silicon. It has a negative electrode mixture layer containing, a negative electrode current collector, and a coating layer formed between the negative electrode mixture layer and the negative electrode current collector, and the coating layer is a Si-based particle, a conductive auxiliary agent, and the like. And an all-solid-state battery containing a polymer.

According to the present disclosure, it is possible to provide an all-solid-state battery capable of suppressing an increase in the internal temperature of the battery.

In the all-solid-state battery of the present disclosure, due to the presence of the coating layer containing Si-based particles formed on the negative electrode current collector, the Si-based particles occlude lithium and expand even if overcharging occurs. Can be done.

It is a schematic sectional drawing which shows an example of the all-solid-state battery in this disclosure. It is a schematic diagram for demonstrating the mechanism that the negative electrode in this disclosure can suppress an increase in a battery internal temperature.

Hereinafter, the all-solid-state battery in the present disclosure will be described in detail.

A. All-solid-state battery The all-solid-state battery in the present disclosure has a positive electrode, a negative electrode, and an electrolyte layer, which will be described later.
FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery in the present disclosure. The all-solid-state battery 10 shown in FIG. 1 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3 formed between the positive electrode 1 and the negative electrode 2. Further, the negative electrode 2 has a negative electrode mixture layer 2a, a coating layer 2b, and a negative electrode current collector 2c. Further, the positive electrode 1 includes a positive electrode active material layer 1a and a positive electrode current collector 1b that collects electricity.

In the all-solid-state battery of the present disclosure, due to the presence of the coating layer containing Si-based particles formed on the negative electrode current collector, the Si-based particles occlude lithium and expand even if overcharging occurs. Can be done. This makes it possible to efficiently cut the electron conduction path even in a region where the internal temperature of the battery does not rise, resulting in a more reliable all-solid-state battery.
Further, in the all-solid-state battery of the present disclosure, since the electron conducting path is cut mainly by the expansion of Si-based particles, a larger amount of conductive auxiliary agent can be added to the coating layer. As a result, the internal resistance during normal use can be lowered, and an all-solid-state battery having better rate characteristics can be obtained.

1. 1. Negative electrode The negative electrode in the present disclosure has a negative electrode mixture layer, a negative electrode current collector, and a coating layer, which will be described later.

(1) Negative electrode mixture layer The negative electrode mixture layer contains a negative electrode active material having a higher lithium occlusion potential than silicon. If such a negative electrode active material is contained, it is possible to prevent Si-based particles contained in the coating layer from reacting with lithium when the battery is normally used. If the Si-based particles react with lithium during normal use, the expansion of the Si-based particles cuts the electron conducting path and increases the internal resistance.

The negative electrode active material is not particularly limited, and examples thereof include Li ₄ Ti ₅ O ₁₂ , TiNb ₂ O ₇ , Ti ₂ Nb ₁₀ O ₂₉ , TiO ₂ , Nb ₂ O ₅ , MoO ₂ , MoO ₃ , and WO ₃ . Can be mentioned.

The ratio of the negative electrode active material in the negative electrode mixture layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the negative electrode active material in the negative electrode mixture layer is, for example, 95% by weight or less, 90% by weight or less, or 80% by weight or less.

Further, the negative electrode mixture layer may contain at least one of a solid electrolyte, a conductive auxiliary agent and a binder, if necessary. Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. Examples of the sulfide solid electrolyte include Li element, X element (X is at least one of P, Si, Ge, Sn, B, Al, Ga, and In), and a solid electrolyte containing S element. Can be mentioned. Further, the sulfide solid electrolyte may further contain at least one of an O element and a halogen element. Examples of the oxide solid electrolyte include Li element, Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O element. Examples thereof include solid electrolytes containing. Examples of the nitride solid electrolyte include Li 3N, and examples of the halide solid electrolyte include LiCl _, LiI, and LiBr.

Examples of the conductive auxiliary agent include carbon materials. Examples of the carbon material include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), carbon fibers, carbon nanotubes (CNT), carbon nanofibers (CNF), and gas phase growth carbon fibers (VGCF). Examples thereof include fibrous carbon materials such as.

Examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF).

(2) Negative electrode current collector For the negative electrode current collector, a metal that can be used as a current collector for an all-solid-state battery can be appropriately used. Such metals include metals containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge and In. The material can be exemplified. The thickness and shape of the negative electrode current collector can be appropriately selected according to the application of the battery.

(3) Coating layer The coating layer is formed between the negative electrode mixture layer and the negative electrode current collector, and contains Si-based particles, a conductive auxiliary agent, and a polymer.
In the present disclosure, the term Si-based particles includes particles such as Si simple substance and Si alloy.

The average particle size (D ₅₀ ) of the Si-based particles is preferably 0.1 μm or more and 3 μm or less, and more preferably 0.5 μm or more and 2 μm or less. If the average particle size is too large, the diffusion of lithium ions in the solid of the Si-based particles in the coating layer is reduced, and the Si-based particles may not be able to occlude lithium efficiently. Further, if the average particle size is too small, the dispersibility of the Si-based particles at the time of preparing the slurry may decrease in the formation of the coating layer.

When the amount of Si-based particles contained in the coating layer is C [mg], the theoretical volume of the negative electrode active material in the negative electrode mixture layer is A [mAh / g], the weight is B [mg], and the Si-based material is Si-based. When the theoretical capacity of the particles is D [mAh / g] and the maximum expansion rate of Si-based particles is E [%], the value of (D × C × E / 400) / (A × B) is 0.04 or more. , 0.5 or less is preferable. In particular, it is preferable to satisfy 0.1 or more and 0.4 or less. For example, in the case of Si single particles, D = 4200 and E = 400. This is because the Si-based particles in the coating layer can be sufficiently expanded, so that the electron conducting path can be cut more efficiently. Further, since the Si-based particles can sufficiently occlude excess lithium, lithium precipitation can be suppressed, and the all-solid-state battery with higher reliability can be obtained.

Examples of the conductive auxiliary agent include the conductive auxiliary agent exemplified in the above “(1) Negative electrode mixture layer”. The content of the conductive auxiliary agent is not particularly limited and can be appropriately adjusted.

The polymer is not particularly limited, but a thermoplastic resin that expands thermally is preferable. This is because the expansion of the resin is added in addition to the expansion of the Si-based particles, so that the electron conducting path in the coating layer can be cut more reliably. Examples of the thermoplastic resin include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polypropylene, acrylonitrile butadiene styrene, and methacrylic resin.

The thickness of the coating layer is preferably 6 μm or less. If the coating layer is too thick, ion conduction will be insufficient and Si-based particles may not react well with lithium ions. Also, the cell energy density may be inadequate.

The method for forming the coating layer is not particularly limited, but a slurry is prepared by mixing Si-based particles, a conductive auxiliary agent, and a polymer with a solvent such as N-methylpyrrolidone, and the slurry is placed on a negative electrode current collector by a doctor blade method or the like. After coating with, it may be dried in an inert atmosphere.

2. 2. Positive Electrode The positive electrode usually has at least a positive electrode active material layer and a positive electrode current collector. Further, the positive electrode active material layer contains at least a positive electrode active material, and may contain at least one of a solid electrolyte, a conductive auxiliary agent, and a binder, if necessary.

Examples of the positive electrode active material include an oxide active material. Examples of the oxide active material include rock salt layered active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , Li ₄ Examples thereof include spinel-type active substances such as Ti ₅ O ₁₂ and Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine-type active substances such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , and LiCoPO ₄ .

Examples of the shape of the positive electrode active material include particles. The average particle size (D ₅₀ ) of the positive electrode active material is not particularly limited, but is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle size (D ₅₀ ) of the positive electrode active material is, for example, 50 μm or less, and may be 20 μm or less.

The ratio of the positive electrode active material in the positive electrode active material layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the positive electrode active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

The solid electrolyte, the conductive auxiliary agent, and the binder used for the positive electrode active material layer are the same as those described in "1. Negative electrode" above, and thus the description thereof is omitted here.

The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less. Examples of the method for forming the positive electrode active material layer include a method of applying a slurry containing a positive electrode active material and a dispersion medium and drying the slurry.

As the positive electrode current collector, a metal that can be used as a current collector for an all-solid-state battery can be appropriately used as described in "1. Negative electrode" above.

3. 3. Solid electrolyte layer The solid electrolyte layer is a layer formed between a positive electrode and a negative electrode. The solid electrolyte layer may contain at least a solid electrolyte and, if necessary, a binder. Since the solid electrolyte and the binder are the same as those described in "1. Negative electrode" above, the description thereof is omitted here. Above all, the solid electrolyte layer preferably contains a sulfide solid electrolyte as the solid electrolyte.

The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less. Examples of the method for forming the solid electrolyte layer include a method of compression molding a solid electrolyte.

4. All-solid-state battery The all-solid-state battery in the present disclosure is preferably an all-solid-state lithium battery. Further, the all-solid-state battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful as an in-vehicle battery, for example. Further, the all-solid-state battery in the present disclosure may be a single battery or a laminated battery. The laminated battery may be a monopolar type laminated battery (parallel connection type laminated battery) or a bipolar type laminated battery (series connection type laminated battery). Examples of the shape of the all-solid-state battery include a coin type, a laminated type, a cylindrical type, and a square type.

Since the conventional battery having a PTC film does not contain Si-based particles (silicon particles), for example, when overcharging occurs, the electron conduction path cannot be cut to the temperature at which the thermoplastic resin expands, and the battery temperature. There was a risk of a rise. In addition, there was a risk that excess lithium would precipitate. However, as shown in FIG. 2, in the all-solid-state battery of the present disclosure, a coating layer having Si-based particles is provided between the negative electrode mixture layer and the negative electrode current collector, and when overcharging occurs, Si-based particles can occlude lithium and expand. Therefore, it is possible to efficiently cut the electron conduction path even in a region where the internal temperature of the battery does not rise, and it is possible to suppress the rise in the battery temperature.

The present disclosure is not limited to the above embodiment. The above-described embodiment is an example, and any technique having substantially the same structure as the technical idea described in the claims of the present disclosure and exhibiting the same action and effect is the present invention. Included in the technical scope of the disclosure.

[Example 1]
(Formation of coating layer on negative electrode current collector)
Furness black (manufactured by Tokai Carbon Co., Ltd.) and silicon (D ₅₀ = 1.2 μm) were prepared as a conductive auxiliary agent, and PVDF-HFP (manufactured by Solvay, Solef (registered trademark); 21510) was prepared as a polymer. A slurry was prepared by mixing silicon, a conductive auxiliary agent and a polymer, and mixing with N-methylpyrrolidone as a solvent.
A copper foil of 15 μm was prepared as a negative electrode current collector, and the slurry prepared on the copper foil by the doctor blade method was applied by adjusting the gap of the doctor blade. After coating, it was dried in a stationary drying oven under an inert atmosphere at 100 ° C. for 1 hour to form a coating layer on the copper foil.

(Manufacturing of negative electrode)
As the negative electrode active material, the weight ratio of Li ₄ Ti ₅ O ₁₂ (LTO) and the sulfide solid electrolyte (10LiI _- 15LiBr _- 75 (3Li 2SP2S ₅ )) is the negative electrode active material: sulfide solid electrolyte = Weighed to 55:45. Further, PVDF-HFP (Solvay Co., Ltd., Solef (registered trademark); 21510) was weighed to 1.5 parts by weight with respect to 100 parts by weight of the negative electrode active material.
Furthermore, methyl isobutyl ketone (dehydration grade; manufactured by Nakaraitesk Co., Ltd.) and n-decane (manufactured by Tokyo Kasei Kogyo Co., Ltd.) dehydrated with molecular sieves are prepared as the main solvent, and the volume ratio is the main. Solvent: Sub-solvent = 90:10 (both Vol.%).
These materials were mixed and kneaded for 1 minute using an ultrasonic homogenizer to prepare a slurry-like negative electrode composition.
Then, a slurry-like negative electrode composition was applied to the surface of the coating layer formed above using a doctor blade, air-dried for 30 minutes, and then heated and dried at 100 ° C. for 30 minutes to prepare a negative electrode. ..

(Preparation of positive electrode)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nichia Chemical Industries, Ltd.) and sulfide solid electrolyte (10LiI-15LiBr-75 (3Li ₂ S-P ₂ S ₅ )) as positive electrode active materials. Weighed so that the weight ratio of positive electrode active material: sulfide solid electrolyte = 75:25. Further, a conductive auxiliary agent (gas phase growth carbon fiber, Showa Denko) so that PVDF-HFP (manufactured by Solvay, Solef (registered trademark); 21510) is 1.5 parts by weight with respect to 100 parts by weight of the positive electrode active material. (Made by Co., Ltd.) was weighed to 3.0 parts by weight.
Furthermore, methyl isobutyl ketone (dehydration grade; manufactured by Nakaraitesk Co., Ltd.) is prepared as the main solvent, and n-decane (manufactured by Tokyo Kasei Kogyo Co., Ltd.) dehydrated with molecular sieves is prepared as the secondary solvent, and the volume ratio is the main solvent. : The mixture was prepared so that the by-solvent = 90:10 (both Vol.%).
These materials were mixed and kneaded for 1 minute using an ultrasonic homogenizer to prepare a slurry-like positive electrode composition.
Then, a slurry-like positive electrode composition was applied to the surface of an aluminum foil (positive electrode current collector) (manufactured by Showa Denko KK) using a doctor blade, air-dried for 30 minutes, and then 30 ° C. A positive electrode was prepared by heating and drying for a minute.

(Making an all-solid-state battery)
In a glove box in an Ar atmosphere, 1 part by weight of PVDF-HFP (Solvay, Solef®; 21510) was added to 100 parts by weight of the sulfide solid electrolyte. Further, the main solvent methyl isobutyl ketone (dehydrated grade, manufactured by Nakaraitesk Co., Ltd.) was added so as to have a solid content of 35 wt% and kneaded using an ultrasonic homogenizer to obtain a slurry for forming a solid electrolyte layer.
A solid electrolyte layer was obtained by applying a slurry for forming a solid electrolyte layer to an aluminum foil using a doctor blade and drying it.
The obtained solid electrolyte layer was punched to 1 cm ² , the aluminum foil was peeled off, the positive electrode and the negative electrode were stacked so as to face each other across the solid electrolyte layer, and then pressed at 4.3 tons to obtain an all-solid-state battery. ..

[Examples 2 to 10]
As shown in Table 1, the type of negative electrode active material can be changed to TiNb ₂ O ₇ (TNO) or TiO ₂ (all in-house synthesized products), and the silicon particle content in the coating layer, the thickness of the coating layer, etc. can be changed. An all-solid-state battery was produced in the same manner as in Example 1 except that it was changed.

[Comparative Examples 1 to 4]
As shown in Table 1, the all-solid-state battery is the same as in the examples except that silicon particles are not used or alumina (CB-P02 manufactured by Showa Denko KK) is used instead of the silicon particles. Was produced.

[evaluation]
Overcharge test Each of the all-solid-state batteries produced in the above Examples and Comparative Examples was charged and discharged once under the following conditions A and B, respectively. Then, an overcharge test was performed under the following condition C, and the rate characteristics (rate maintenance rate) before and after the overcharge test were compared. The results are shown in Table 1.
If the rate maintenance rate before overcharging is high, it means that the internal resistance is low. If the rate maintenance rate after overcharging is low, it means that the internal resistance is increasing. That is, if the rate maintenance rate after overcharging is sufficiently lower than the rate maintenance rate before overcharging, it can be seen that the electronic conduction path is disconnected.
Condition A
Charging voltage: 3.0V (CCCV 0.01C cut)
Discharge voltage: 1.5V (CCCV 0.01C cut)
Current density: 0.1C or 3C equivalent Condition B
Charging voltage: 3.0V (CC voltage cut)
Discharge voltage: 1.5V (CCCV 0.01C cut)
Current density: 0.1C equivalent condition C
Charging voltage: 4.0V (CC voltage cut)
Discharge voltage: 1.5V (CCCV 0.01C cut)
Current density: equivalent to 0.1C

High temperature storage test The batteries of Comparative Examples 1 to 4 which were overcharged by the above overcharge test were stored in a constant temperature bath at 110 ° C. for 1 hour. This is a test that simulates the heat generation of a large battery when an overcharge test is performed. After high-temperature storage, it was discharged once, charged and discharged under the condition A of the overcharge test, and the 3C discharge capacities before and after storage were compared.

Precipitation of lithium The above-mentioned overcharge test was performed, the exterior of the overcharged battery was peeled off, the negative electrode mixture layer was scraped off, and electron spin resonance (ESR) measurement was performed. Specific ESR measurement conditions were carried out according to a general method. When metallic lithium is deposited in the ESR measurement, a signal with a very narrow line width is observed near g = 2.00225. Table 1 shows the presence or absence of lithium precipitation. A battery in which a signal was detected (a battery in which lithium was deposited) was indicated by "x", and a battery in which no signal was detected (a battery in which lithium was not deposited) was indicated by "○".

As shown in Table 1, in Examples 1 to 10, the rate maintenance rate after overcharging was 28% or more lower than the rate maintenance rate before overcharging, so that the electronic conduction path was sufficiently cut off. It turned out that.
On the other hand, it was found that the coating layer does not contain silicon particles, that is, in the comparative example using the conventional PTC film, the rate maintenance rate before and after overcharging is almost the same, and the cutting of the electron conducting path is insufficient. rice field. In addition, the precipitation of lithium was also remarkable. The rate maintenance rate after the high temperature storage test was reduced to a value close to that of the examples. That is, in the prior art, when overcharging, the battery reaction cannot be stopped until the battery temperature becomes high, and the temperature rise of the battery cannot be suppressed.
Based on the above results, the all-solid-state battery of the present disclosure is superior in safety and more reliable because it can cut the electronic conduction path and stop the battery reaction before the temperature becomes high when overcharging occurs. Was found to be improving.

1 ... Positive electrode 1a ... Positive electrode active material layer 1b ... Positive electrode current collector 2 ... Negative electrode 2a ... Negative electrode mixture layer 2b ... Coating layer 2c ... Negative electrode current collector 3 ... Solid electrolyte layer 10 ... All-solid-state battery

Claims (1)

An all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer formed between the positive electrode and the negative electrode.
The negative electrode is a negative electrode mixture layer containing a negative electrode active material having a lithium occlusion potential higher than that of silicon, a negative electrode current collector, and a coating layer formed between the negative electrode mixture layer and the negative electrode current collector. Have,
An all-solid-state battery in which the coating layer contains Si-based particles having a lithium occlusion potential of silicon or less, a conductive auxiliary agent, and a polymer.

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