JP6909411B2 - All solid state battery - Google Patents

Description

The present invention relates to an all-solid-state battery.

In recent years, the development of all-solid-state batteries having a solid electrolyte layer is accelerating amid demands for improved reliability and cost reduction of secondary batteries. For example, Patent Document 1 discloses an all-solid-state battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode and the negative electrode. Patent Document 1 describes that the precipitation of dendrite-like metallic lithium (Lidendrite) can be suppressed by using a mixture of metallic lithium and carbon black as the negative electrode active material.

Japanese Unexamined Patent Publication No. 2016-100088

However, according to the study of the present inventor, when the technique of Patent Document 1 is applied to a battery (for example, an in-vehicle battery) used in a mode of repeating high-rate charging / discharging, there is room for further improvement. That is, when the battery is rapidly charged or discharged, Li ions tend to be biased toward one of the electrodes, and the precipitation and growth of Lidendrite tend to occur. Therefore, it has been required to maintain the high-rate charge / discharge characteristics and suppress a short circuit between the positive electrode and the negative electrode even when the lidendrite is precipitated and grown. In other words, it has been required to improve the precipitation resistance of Lidendrite.

The present invention has been made in view of the above points, and an object of the present invention is to provide an all-solid-state battery having excellent precipitation resistance of Lidendrite.

According to the present invention, a positive electrode mixture layer containing a positive electrode active material, a negative electrode mixture layer containing a negative electrode active material, and a solid electrolyte layer arranged between the positive electrode mixture layer and the negative electrode mixture layer in the stacking direction. And, an all-solid-state battery is provided. The solid electrolyte layer has a Li storage layer containing a solid electrolyte material and lithium titanate in a part of the stacking direction. In the Li storage layer, the solid electrolyte material has a bimodal particle size distribution, and the two peak tops are in the range of 0.5 μm or more and 1 μm or less and in the range of 3 μm or more and 6 μm or less, respectively. And. The average particle size of the lithium titanate is 0.2 μm or more and 0.4 μm or less.

The all-solid-state battery has a Li storage layer in the solid electrolyte layer. As a result, when Li dendrite is generated and grows to reach the Li occlusion layer, Li is occluded in the Li occlusion layer, and further growth of Li dendrite is suppressed. As a result, the insulating property between the positive electrode and the negative electrode can be suitably maintained even in the mode of repeating high-rate charging / discharging. Further, the increase in resistance due to the formation of the Li storage layer can be suppressed to a small value, and the high-rate charge / discharge characteristics can be maintained.

It is a schematic cross-sectional view of the all-solid-state battery which concerns on one Embodiment.

Hereinafter, preferred embodiments of the all-solid-state battery disclosed herein will be described. It should be noted that the embodiments described here are, of course, not intended to particularly limit the present invention. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The all-solid-state battery disclosed here can be implemented based on the contents disclosed in the present specification and the common general technical knowledge in the art. Further, when the numerical range is described as A to B (where A and B are arbitrary numerical values) in this specification, it means A or more and B or less.

FIG. 1 is a schematic cross-sectional view of the all-solid-state battery 1. The all-solid-state battery 1 includes a positive electrode 2, a negative electrode 4, and a solid electrolyte layer 6. In FIG. 1, the reference numeral X means the stacking direction of the positive electrode 2 and the negative electrode 4 and the thickness direction of each layer. In the stacking direction X, the solid electrolyte layer 6 is arranged between the positive electrode 2 and the negative electrode 4. The positive electrode 2, the negative electrode 4, and the solid electrolyte layer 6 are physically integrated. The all-solid-state battery 1 is typically a rechargeable and dischargeable secondary battery, such as a lithium ion secondary battery.

The positive electrode 2 includes a positive electrode current collector 21 and a positive electrode mixture layer 22 fixed to one surface of the positive electrode current collector 21. The positive electrode current collector 21 is a conductive member. Although not shown, the positive electrode current collector 21 is electrically connected to the positive electrode terminal for external connection. The positive electrode current collector 21 is made of a metal having good conductivity, such as Al, Ti, and stainless steel (SUS). The positive electrode 2 does not have to have the positive electrode current collector 21. Further, the positive electrode mixture layer 22 may be fixed to both surfaces of the positive electrode current collector 21.

The positive electrode mixture layer 22 contains at least the positive electrode active material. The positive electrode active material is a material capable of reversibly storing and releasing charge carriers (for example, lithium ions). Examples of the positive electrode active material include metal oxides containing one or more kinds of metal elements and oxygen elements. The metal oxide may be a compound containing a lithium element, one or more kinds of transition metal elements, and an oxygen element. As a preferred example of the metal oxide, lithium transition such as lithium nickel-containing composite oxide, lithium cobalt-containing composite oxide, lithium nickel cobalt-containing composite oxide, lithium manganese-containing composite oxide, and lithium nickel cobalt manganese-containing composite oxide. Examples include metal composite oxides.

The positive electrode mixture layer 22 may contain other components, for example, a solid electrolyte material, a binder, a conductive material, various additives, and the like, if necessary, in addition to the positive electrode active material. Examples of the solid electrolyte material include sulfide solid electrolyte materials, oxide solid electrolyte materials, nitride solid electrolyte materials, and halide solid electrolyte materials. More specifically, examples of the constituent material of the solid electrolyte layer 6 include a sulfide solid electrolyte material described later. Examples of the binder include vinylidene fluoride (PVdF), vinyl halide resins such as a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP), acrylate-butadiene rubber (ABR), and styrene-butadiene rubber (SBR). , Acrylonitrile-butadiene rubber (NBR) and other rubbers are exemplified. Examples of the conductive material include carbon materials such as vapor-phase carbon fiber and carbon black.

The negative electrode 4 includes a negative electrode current collector 41 and a negative electrode mixture layer 42 fixed to one surface of the negative electrode current collector 41. The negative electrode current collector 41 is a conductive member. Although not shown, the negative electrode current collector 41 is electrically connected to the negative electrode terminal for external connection. The negative electrode current collector 41 is made of a metal having good conductivity, such as Cu, Ti, or stainless steel (SUS). The negative electrode 4 does not have to have the negative electrode current collector 41. Further, the negative electrode mixture layer 42 may be fixed to both surfaces of the negative electrode current collector 41.

The negative electrode mixture layer 42 contains at least the negative electrode active material. The negative electrode active material is a material capable of reversibly storing and releasing charge carriers (for example, lithium ions). Examples of the negative electrode active material include metal materials such as Si, Ti, In, and Sn, metal compounds containing the above metal elements, metal oxides, Li metal compounds, Li metal oxides, and carbon materials such as hard carbon and graphite. Can be mentioned. The negative electrode active material may be, for example, a Si-based material in which silicon (Si) accounts for approximately 50% by mass or more. The ratio of Si to the entire negative electrode active material may be, for example, 80% by mass or more. The Si-based material may be at least one of Si, a Si alloy, a Si compound and a Si mixture.

The negative electrode mixture layer 42 may contain other components, for example, a solid electrolyte material, a binder, a conductive material, various additives, and the like, if necessary, in addition to the negative electrode active material. Examples of the solid electrolyte material include sulfide solid electrolyte materials, oxide solid electrolyte materials, nitride solid electrolyte materials, and halide solid electrolyte materials. More specifically, examples of the constituent material of the solid electrolyte layer 6 include a sulfide solid electrolyte material described later. Examples of the binder include vinylidene fluoride (PVdF), vinyl halide resins such as a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP), acrylate-butadiene rubber (ABR), and styrene-butadiene rubber (SBR). , Acrylonitrile-butadiene rubber (NBR) and other rubbers are exemplified. Examples of the conductive material include carbon materials such as vapor-phase carbon fiber and carbon black.

The solid electrolyte layer 6 is arranged between the positive electrode mixture layer 22 and the negative electrode mixture layer 42, and insulates the positive electrode 2 and the negative electrode 4. The solid electrolyte layer 6 has Li ion conductivity. The solid electrolyte layer 6 is in a solid state at room temperature (25 ° C.). The solid electrolyte layer 6 of the present embodiment has a first solid electrolyte layer 61, a second solid electrolyte layer 62, and a Li storage layer 63. The first solid electrolyte layer 61 and the second solid electrolyte layer 62 are each insulating. The first solid electrolyte layer 61 and the second solid electrolyte layer 62 may be equivalent to the conventionally known solid electrolyte layer. The Li storage layer 63 is a portion capable of storing Li. In the stacking direction X, the Li storage layer 63 is arranged between the first solid electrolyte layer 61 and the second solid electrolyte layer 62. In other words, the Li storage layer 63 is arranged in the middle of the stacking direction X of the solid electrolyte layer 6. The Li storage layer 63 is arranged in a part of the stacking direction X. The thickness of the Li storage layer 63 is smaller than the total thickness of the solid electrolyte layer 6. The Li storage layer 63 is insulating before storing Li. The Li occlusion layer 63 may have electrical conductivity when it occludes Li. The solid electrolyte layer 6 does not have to have the first solid electrolyte layer 61 or the second solid electrolyte layer 62. Further, in the stacking direction X, the Li storage layer 63 may be in contact with the positive electrode mixture layer 22 or the negative electrode mixture layer 42.

The first solid electrolyte layer 61, the second solid electrolyte layer 62, and the Li storage layer 63 each contain at least a solid electrolyte material. The solid electrolyte materials contained in the first solid electrolyte layer 61, the second solid electrolyte layer 62, and the Li storage layer 63 may be the same or different. The solid electrolyte material may be glassy (amorphous), crystallized glassy, or crystalline. The solid electrolyte material may be, for example, a sulfide solid electrolyte material, an oxide solid electrolyte material, a nitride solid electrolyte material, a halide solid electrolyte material, or the like. The Li ion conductivity of the solid electrolyte material is preferably, for example, 1 × 10 ^-5 S / cm or more, and further preferably 1 × 10 ^-4 S / cm or more at room temperature (25 ° C.). The first solid electrolyte layer 61, the second solid electrolyte layer 62, and the Li storage layer 63 may contain the same type of solid electrolyte material. For example, the first solid electrolyte layer 61, the second solid electrolyte layer 62, and the Li storage layer 63 may all contain a sulfide solid electrolyte material.

Examples of the sulfide solid electrolyte material include Li ₂ S-P ₂ S ₅ series materials; Li ₂ S-GeS ₂ series materials; Li ₂ S-GeS _2- P ₂ S ₅ series materials; Li ₃ PO _4- P. ₂ S ₅ based material; sulfide material and the like. Further, a halogen-added sulfide material obtained by adding a halogen element to the sulfide material is also suitable. As an example of the halogenated sulfide material, the following formula: Li _7-x PS _6-x A _x (where x is 0.1 ≦ x ≦ 2, for example 0.2 ≦ x ≦ 1.8. A is a compound represented by at least one of halogen elements, for example, at least one of Cl, Br and I).

In the present embodiment, the solid electrolyte material contained in the Li storage layer 63 is in the form of particles and has a bimodal particle size distribution. In other words, in the graph of particle size distribution in which the horizontal axis represents the particle size (μm) and the vertical axis represents the frequency, the first peak having a relatively small particle size and the second peak having a relatively large particle size Has. The solid electrolyte material contained in the Li storage layer 63 has a first peak top (maximum value of the peak) in the range of 0.5 to 1 μm and a second peak top (maximum value of the peak) of 3. It is in the range of ~ 6 μm. Since the solid electrolyte material has a bimodal particle size distribution, particles having a small particle size are arranged so as to fill the gaps between the particles having a large particle size, and the packing property (packing property) is improved. As a result, it is possible to form a dense Li storage layer 63 in which Li dendrite does not easily penetrate. Further, when the position of the peak top is in the above range, the integrity of the Li storage layer 63 can be enhanced and the interfacial resistance between the particles of the solid electrolyte material can be suppressed low. The two peak tops may be more frequent, but the second peak is preferably more frequent. Thereby, the internal resistance of the Li storage layer 63 can be better reduced.

Although not particularly limited, in the graph of the particle size distribution in which the horizontal axis represents the particle size (μm) and the vertical axis represents the frequency, the ratio of the area of the first peak to the area of the second peak is determined. The first peak: the second peak = 20:80 to 80:20, preferably the first peak: the second peak = 20:80 to 60:40, and more preferably the first peak. The peak of 1: the second peak = 20:80 to 40:60. Thereby, the internal resistance of the Li storage layer 63 can be better reduced.

In the present embodiment, the Li storage layer 63 contains lithium titanate (LTO) as an essential component in addition to the above-mentioned solid electrolyte material. Lithium titanate is a Li occlusion substance capable of occlusion of Li. Lithium titanate is in the form of particles. The average particle size of lithium titanate is 0.2 to 0.4 μm. By setting the average particle size to a predetermined value or more, the interfacial resistance between lithium titanate can be suppressed and the internal resistance of the Li storage layer 63 can be reduced. By setting the average particle size to a predetermined value or less, the growth of Lidendrite can be stably suppressed. In the present specification, the "average particle size" is a particle size corresponding to an integrated 50% from the smaller particle size side in the volume-based particle size distribution obtained by the particle size distribution measurement based on the laser diffraction / light scattering method. To say.

Although not particularly limited, when the total solid content of the Li storage layer 63 is 100% by mass, the content of the solid electrolyte material is approximately 10 to 90% by mass, typically 20 to 80% by mass. For example, it may be 30 to 70% by mass, and further 40 to 60% by mass. Although not particularly limited, the content of lithium titanate is approximately 10 to 90% by mass, typically 20 to 80% by mass, when the total solid content of the Li storage layer 63 is 100% by mass. For example, it may be 30 to 70% by mass, and further 40 to 60% by mass. The content of the solid electrolyte material may be higher than the content of lithium titanate.

The first solid electrolyte layer 61, the second solid electrolyte layer 62, and the Li storage layer 63 may each contain components other than those described above, for example, a binder, various additives, and the like, if necessary. Examples of the binder include vinylidene fluoride (PVdF), vinyl halide resins such as a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP), acrylate-butadiene rubber (ABR), and styrene-butadiene rubber (SBR). , Acrylonitrile-butadiene rubber (NBR) and other rubbers are exemplified.

As described above, the solid electrolyte layer 6 of the all-solid-state battery 1 has a Li storage layer 63. The Li storage layer 63 is formed by densely packing the above-mentioned lithium titanate having an average particle size and the above-mentioned solid electrolyte material having a bimodal particle size distribution. As a result, when the Li dendrite reaches the Li storage layer 63, Li is suitably stored in the Li storage layer 63, and the growth of the Li dendrite is suppressed. As a result, it is possible to prevent the Li dendrite from penetrating the Li storage layer 63 and suppress a short circuit between the positive electrode 2 and the negative electrode 4. Further, in the Li storage layer 63, the interfacial resistance between the lithium titanate particles is reduced, and the increase in resistance is suppressed to be small. As a result, the all-solid-state battery 1 can suitably exhibit high battery characteristics (for example, high-rate charge / discharge characteristics).

The all-solid-state battery 1 disclosed herein can be used for various purposes. For example, it can be suitably used as a power source (driving power source) for a motor mounted on a vehicle. The type of vehicle is not particularly limited, but typically examples thereof include automobiles such as plug-in hybrid vehicles (PHVs), hybrid vehicles (HVs), and electric vehicles (EVs).

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such specific examples.

[Preparation of positive electrode]
First, in an inert gas, lithium nickel cobalt manganese-containing composite oxide as a positive electrode active material, Li ₆ PS ₅ Br as a solid electrolyte material, ABR as a binder, and vapor phase carbon fiber as a conductive material. And were mixed. A positive electrode slurry was prepared by adding a solvent to this mixture and kneading it. This positive electrode slurry was applied to the surface of an aluminum foil (positive electrode current collector), air-dried, and then heat-dried at 120 ° C. As a result, a positive electrode having a positive electrode mixture layer fixed on the positive electrode current collector was produced.

[Preparation of negative electrode]
First, in an inert gas, Si as a negative electrode active material, Li ₆ PS ₅ Br as a solid electrolyte material, ABR as a binder, and vapor phase carbon fiber as a conductive material were mixed. A negative electrode slurry was prepared by adding a solvent to this mixture and kneading it. This negative electrode slurry was applied to the surface of a copper foil (negative electrode current collector), air-dried, and then heat-dried at 120 ° C. As a result, a negative electrode having a negative electrode mixture layer fixed on the negative electrode current collector was produced.

[Formation of solid electrolyte layer]
Next, in an inert gas atmosphere _{, the mass ratio of Li 6} PS ₅ Br as a solid electrolyte material and ABR as a binder is such that the mass ratio is solid electrolyte material: binder = 99.4: 0.6. Mixed. A solid electrolyte slurry was prepared by adding a solvent to this mixture and kneading it. This solid electrolyte slurry was applied to the surface of the positive electrode mixture layer of the positive electrode and the surface of the negative electrode mixture layer of the negative electrode, respectively, and naturally dried, and then heated and dried at 120 ° C. As a result, a positive electrode with a first solid electrolyte layer and a negative electrode with a second solid electrolyte layer were obtained. The first solid electrolyte layer and the second solid electrolyte layer have the same composition and the same thickness, but are described as first and second for the sake of distinction.

Next, in Comparative Example 1, under an inert gas atmosphere, two types of Li ₆ PS ₅ Br as a solid electrolyte material (SSE) and ABR as a binder have a mass ratio shown in Table 1. Mixed. Further, in Examples 1 to 8 and Comparative Examples 2 to 4, lithium titanate (LTO) as a Li occlusion substance and Li ₆ PS ₅ Br as a solid electrolyte material (SSE) were used in an inert gas atmosphere. ABR as a binder was mixed so as to have the mass ratio shown in Table 1. As SSE, as shown in Table 1, two types of materials (SSE1 and SSE2) having different average particle sizes were prepared, and one or both of them were used. A slurry was prepared by adding a solvent to this mixture and kneading it. This slurry was applied to the surface of an aluminum foil (supporting base material), air-dried, and then heat-dried at 120 ° C. As a result, a third solid electrolyte layer was formed on the supporting base material.

[Construction of all-solid-state battery]
A positive electrode with the first solid electrolyte layer was superposed on the prepared third solid electrolyte layer, and pressed at ^{25 ° C. under the condition of a surface pressure of 1 ton / cm 2.} At this time, the positive electrode was arranged so that the side of the first solid electrolyte layer faces the third solid electrolyte layer. Next, the supporting base material attached to the surface of the third solid electrolyte layer was peeled off, the negative electrode with the second solid electrolyte layer was placed on the exposed surface of the third solid electrolyte layer, and the surface pressure was 1 ton / cm at 25 ° C. Pressed under the condition of ^2. At this time, the negative electrode was arranged so that the side of the second solid electrolyte layer faces the third solid electrolyte layer. In this way, an all-solid-state battery having a laminated structure in which the positive electrode, the first solid electrolyte layer, the third solid electrolyte layer, the second solid electrolyte layer, and the negative electrode are laminated in this order in the stacking direction (eg, 1 to 8 and Comparative Examples 1 to 4) were constructed.

≪Evaluation of resistance≫
At 25 ° C., the initial resistance of the above-constructed all-solid-state batteries (Examples 1 to 8 and Comparative Examples 1 to 4) was measured. Specifically, first, the battery voltage was adjusted to 3.6V. Next, a current of 5 mA was applied for 5 seconds, and the change in battery voltage at this time was measured. Then, the resistance value was calculated by dividing the amount of change in the battery voltage by the applied current (5 mA). The results are shown in Table 1.

≪Evaluation of short circuit resistance during high temperature storage≫
First, at 25 ° C., the following (1) to (4): (1) CC charging is performed with respect to the above-constructed all-solid-state battery (Examples 1 to 8 and Comparative Examples 1 to 4), assuming that the center voltage of the battery is 4 V. : Constant current charge at a rate of 10C for 0.1 seconds; (2) Pause; (3) CC discharge: Constant current discharge at a rate of 0.1C for 10 seconds; (4) Pause; A total of 100 cycles of pulse charging and discharging were performed. Next, the all-solid-state battery after the pulse charge / discharge was CC-charged at a rate of 0.01 C until the battery voltage became 4.0 V, and then stored in a constant temperature bath at 60 ° C. for 48 hours. Then, the presence or absence of a short circuit was evaluated. The results are shown in Table 1. In Table 1, when the storage is started at 60 ° C. and the amount of voltage change between 24 hours and 48 hours is 0.2 V or more, the short circuit is “Yes”, and the case where the voltage is less than 0.2 V is short-circuited. Short circuit "None" is shown.

As shown in Table 1, Comparative Example 1 in which the LTO was not contained in the third solid electrolyte layer, Comparative Example 3 in which the LTO having a large average particle size of 0.5 μm was used in the third solid electrolyte layer, and the third solid. In Comparative Example 4, in which the particle size distribution of the solid electrolyte material contained in the electrolyte layer was monomodal, the resistance was suppressed to a low level, but a short circuit occurred during high-temperature storage. It is considered that the reason for this is that in Comparative Example 3, since the average particle size of LTO was large, the Li storage capacity of LTO was not exhibited well and the growth of Lidendrite could not be suppressed. Further, in Comparative Example 4, since the particle size distribution of the solid electrolyte material was monomodal with an average particle size of 3 μm, the denseness of the third solid electrolyte layer was lowered, and the growth of Lidendrite could not be suppressed. It is also possible that Lidendrite penetrated the third solid electrolyte layer. On the other hand, in Comparative Example 2 in which LTO having a small average particle size of 0.1 μm was used for the third solid electrolyte layer, a short circuit during high temperature storage was not observed, but the resistance increase was remarkable as compared with Comparative Example 1. .. The reason for this is considered to be that the resistance of the third solid electrolyte layer increased as a result of the increase in the interface between the LTO particles.

Compared to these Comparative Examples 1 to 4, in the third solid electrolyte layer (Li storage layer), the particle size distribution of the solid electrolyte material is bimodal with peak tops at 0.5 to 1 μm and 3 to 6 μm, and is bimodal. In Examples 1 to 8 in which the average particle size of the LTO was 0.2 to 0.4 μm, the short-circuit resistance during high-temperature storage was excellent. Further, in Examples 1 to 8, the resistance was suppressed to be relatively low as compared with Comparative Example 2. Such results show the significance of the techniques disclosed herein.

Although the present invention has been described in detail above, the above-described embodiments and examples are merely examples, and the inventions disclosed herein include various modifications and modifications of the above-mentioned specific examples.

1 All-solid-state battery 2 Positive electrode 4 Negative electrode 6 Solid electrolyte layer 63 Li occlusion layer

Claims (1)

A positive electrode mixture layer containing a positive electrode active material and
Negative electrode mixture layer containing negative electrode active material and
A solid electrolyte layer arranged between the positive electrode mixture layer and the negative electrode mixture layer in the stacking direction,
With
The solid electrolyte layer has a Li storage layer containing a solid electrolyte material and lithium titanate in a part of the stacking direction.
In the Li occlusion layer
The solid electrolyte material has a bimodal particle size distribution, and the two peak tops are in the range of 0.5 μm or more and 1 μm or less and in the range of 3 μm or more and 6 μm or less, respectively.
The average particle size of the lithium titanate is 0.2 μm or more and 0.4 μm or less.
All solid state battery.

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