JP7655290B2 - Electrolyte Materials - Google Patents

Description

This disclosure relates to electrolyte materials.

Patent Document 1 (JP Patent Publication No. 2019-503050) discloses an electrolyte material that includes ion-conductive ceramic particles dispersed in a matrix of an ion-conductive solid polymer, an electrolyte salt, and a chemical additive.

Special table 2019-503050 publication

The electrolyte material described in Patent Document 1 contains an ionically conductive solid polymer and ionically conductive ceramic particles, which makes it possible to improve the conductivity of a polymer material that has low conductivity. However, there is room for improvement in the conductivity.

Therefore, the objective of the present disclosure is to provide an electrolyte material with high ionic conductivity.

The technical configuration and effects of the present disclosure are explained below. However, the mechanism of action in this specification includes assumptions. The mechanism of action does not limit the technical scope of the present disclosure.

[1] An electrolyte material comprising a sulfide solid electrolyte and a polymer,
The sulfide solid electrolyte has an average particle size of less than 0.2 μm;
The content of the sulfide solid electrolyte in the electrolyte material is 20% by volume or more and less than 90% by volume,
The polymer includes a dispersion medium and a binder particle group,
The binder particle group includes a fluorine-containing polymer material.

Generally, polymers have low ionic conductivity, so adding a solid electrolyte improves ionic conductivity. Among solid electrolytes, it is considered preferable to use a sulfide solid electrolyte, which has high ionic conductivity. In addition, from the viewpoint of reactivity with the sulfide solid electrolyte, a fluorine-containing polymer material is suitable as the binder particle group in the polymer.

On the other hand, there is a risk that the ionic conductivity will decrease depending on the size and content of the sulfide solid electrolyte. Therefore, it is considered necessary to keep the size and content of the sulfide solid electrolyte within a specified range.

[2] The sulfide solid electrolyte is represented by the following formula (1):
vLiI-wLiBr-(100-vw) (Li ₂ S-P ₂ S ₅ ) (1)
having a composition represented by
In the above formula (1),
v represents the molar fraction percentage of the component derived from LiI, and satisfies the relationship of 10≦v≦20;
w represents the molar fraction percentage of the component derived from LiBr, and satisfies the relationship of 0≦w≦15;
The electrolyte material according to [1], wherein (100-v-w) indicates the percentage of the molar fraction of the component derived from Li ₂ S—P ₂ S ₅ .

[3] The dispersion medium contains butyl acetate,
The electrolyte material according to [1] or [2], wherein the binder particle group contains polyvinylidene fluoride.

[4] An electrolyte material comprising a sulfide solid electrolyte and a polymer,
The sulfide solid electrolyte has an average particle size of 0.1 μm or less,
The content of the sulfide solid electrolyte in the electrolyte material is 30% by volume or more and 80% by volume or less,
The sulfide solid electrolyte has the following formula (1):
vLiI-wLiBr-(100-vw) (Li ₂ S-P ₂ S ₅ ) (1)
having a composition represented by
In the above formula (1),
v represents the molar fraction percentage of the component derived from LiI, and satisfies the relationship of 10≦v≦20;
w represents the molar fraction percentage of the component derived from LiBr, and satisfies the relationship of 0≦w≦15;
(100-v-w) indicates the mole fraction percentage of the component derived from Li ₂ S-P ₂ S ₅ ,
The dispersion medium comprises butyl acetate,
The binder particles include polyvinylidene fluoride.

FIG. 1 is a schematic diagram showing the electrolyte material of the present embodiment. FIG. 2 is a conceptual diagram showing the all-solid-state battery according to the present embodiment.

Below, an embodiment of the present disclosure (hereinafter may be abbreviated as "this embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "this example") are described. However, this embodiment and this example do not limit the technical scope of the present disclosure.

<Electrolyte material>
The electrolyte material of the present embodiment may be used, for example, to form a separator of an all-solid-state battery. However, the electrolyte material of the present embodiment may be applied to any application. The electrolyte material of the present embodiment may be used, for example, to form an electrode of an all-solid-state battery.

Figure 1 is a schematic diagram showing the electrolyte material of this embodiment. The electrolyte material 5 includes a sulfide solid electrolyte 1 and a polymer 2. In the electrolyte material 5, the sulfide solid electrolyte 1 may be dispersed inside the polymer 2. Hereinafter, the solid electrolyte may be abbreviated as "SE" and the sulfide solid electrolyte may be abbreviated as "sulfide SE".

(Sulfide solid electrolyte)
The sulfide SE has high ionic conductivity. The sulfide SE can form an ionic conduction path in the electrolyte material. The sulfide SE includes sulfur (S). The sulfide SE may further include, for example, lithium (Li) or phosphorus (P). The sulfide SE may further include, for example, oxygen (O), silicon (Si), or the like. The sulfide SE may further include, for example, a halogen such as iodine (I) or bromine (Br).

The sulfide SE may be, for example, in a glass state. The sulfide SE may form, for example, glass ceramics (also called "crystallized glass").

The sulfide SE can be synthesized by a mechanochemical method. For example, the raw materials may be mixed using a planetary ball mill, an ultrasonic dispersing device, or the like. In the mechanochemical method, mechanical energy is applied to the mixture, which can homogenize the composition of the mixture and cause the mixture to enter a glassy state. Furthermore, glass ceramics can be formed by subjecting the glassy mixture to an appropriate heat treatment.

The composition of the sulfide SE is represented by the mole fraction of the raw materials. The raw materials may include lithium phosphorus sulfide (e.g., Li ₂ S-P ₂ S ₅ , etc.) and lithium halide (e.g., lithium iodide (LiI), lithium bromide (LiBr), etc.).

The composition of the sulfide SE may be represented, for example, by the following formula (1).
vLiI-wLiBr-(100-vw) (Li ₂ S-P ₂ S ₅ ) (1)
In the above formula (1), "v" indicates the molar fraction (mol%) of the component derived from LiI. "v" may satisfy the relationship of, for example, "10≦v≦20". For example, when "v=10", it indicates that the molar fraction of LiI is 10 mol% with respect to the entire raw material.

"w" indicates the molar fraction of the component derived from LiBr. "w" may satisfy the relationship of "0≦w≦15", for example. For example, when "w=10", it indicates that the molar fraction of LiBr is 10 mol% with respect to the entire raw material.

"(100-v-w)" indicates the molar fraction of the component derived from Li ₂ S-P ₂ S _5. For example, when "v = w = 10", the molar fraction of Li ₂ S-P ₂ S ₅ is 80 mol% with respect to the entire raw material.

The sulfide SE may be, for example, 10LiI-10LiBr-80 (Li ₂ S-P ₂ S ₅ ), 15LiI-5LiBr-80 (Li ₂ S-P ₂ S ₅ ), 10LiI-15LiBr-75 (Li ₂ S-P ₂ S ₅ ), 15LiI-10LiBr-75 (Li ₂ S-P ₂ S ₅ ), 20LiI-5LiBr-75 (Li ₂ S-P ₂ S ₅ ), etc.

Li ₂ S-P ₂ S ₅ can be produced by a mechanochemical reaction between lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ). Lithium phosphorus sulfide may have a composition such as Li ₃ PS ₄ , Li ₄ P ₂ S ₆ , Li ₇ P ₃ S _11, etc.

The composition of lithium phosphorus sulfide may also be expressed by the molar fraction of the raw materials. In this embodiment, the mixing ratio of Li ₂ S and P ₂ S ₅ is arbitrary. For example, in the case of "0.75Li ₂ S-0.25P ₂ S ₅ ", the molar fraction of the component derived from Li ₂ S is 0.75 with respect to the entire raw material of lithium phosphorus sulfide, and the molar fraction of the component derived from P ₂ S ₅ is 0.25 with respect to the entire raw material of lithium phosphorus sulfide. Here, the entire raw material of lithium phosphorus sulfide (the sum of Li ₂ S and P ₂ S ₅ ) is defined as 1.00.

The composition of the lithium phosphorus sulfide may be represented, for example, by the following formula (2).
uLi ₂ S-(1-u)P ₂ S ₅ (2)
In the above formula, "u" represents the molar fraction of the component derived from Li ₂ S. "(1-u)" represents the molar fraction of the component derived from P ₂ S _5. "u" may satisfy the relationship of, for example, "0.5≦u≦0.9".

The lithium phosphorus sulfide may be _, for example _{, 0.5Li2S} - _{0.5P2S5 , 0.6Li2S} - _0.4P2S5 , _0.7Li2S - _0.3P2S5 , _0.75Li2S - _0.25P2S5 , _{0.8Li2S - 0.2P2S5} , _0.9Li2S - _{0.1P2S5 , etc.}

The average particle size (D50) of the sulfide SE is less than 0.2 μm. When the D50 of the sulfide SE is less than 0.2 μm, the sulfide SE is easily dispersed inside the polymer. The D50 of the sulfide SE is preferably 0.1 μm or less. There is no particular limit to the lower limit of the D50 of the sulfide SE, but from the viewpoint of production, it may be, for example, 0.01 μm or more. Here, D50 indicates the particle size at which the cumulative frequency from the small particle size side reaches 50% in the volume-based particle size distribution. D50 can be measured by a laser diffraction method.

The sulfide SE content in the electrolyte material is 20% by volume or more and less than 90% by volume. If the sulfide SE content in the electrolyte material is less than 20% by volume, it is difficult to form an ion conduction path in the electrolyte material, and ion conductivity may decrease. If the sulfide SE content in the electrolyte material is 90% by volume or more, the sulfide SE content is too high and the electrolyte material may not be formed. It is preferable that the sulfide SE content in the electrolyte material is 30% by volume or more and less than 80% by volume.

(polymer)
The polymer includes a dispersion medium and a binder particle group. The polymer may be substantially composed of a dispersion medium and a binder particle group. The polymer may be composed of, for example, 15% by mass or less of the binder particle group and the remaining dispersion medium. By having the mass fraction of the binder particle group be 15% by mass or less, moderate fluidity and dispersion stability are expected. The polymer may be composed of, for example, 1% by mass to 15% by mass of the binder particle group and the remaining dispersion medium.

The dispersion medium is a liquid. The dispersion medium may contain any component. The dispersion medium may contain, for example, a carboxylic acid ester. The dispersion medium may contain, for example, ethyl acetate, butyl acetate, butyl butyrate, pentyl butyrate, butyl pentanoate, pentyl pentanoate, butyl hexanoate, pentyl hexanoate, etc. It is preferable that the dispersion medium contains butyl butyrate. The dispersion medium may consist essentially of butyl butyrate. Butyl butyrate tends to have low reactivity with sulfide SE.

The binder particle group is a dispersoid. The binder particle group is dispersed in a dispersion medium. The binder particle group can bond objects together.

In the binder particle group, each of the particles includes a fluorine-containing polymer material. That is, the binder particle group includes a fluorine-containing polymer material. Each of the particles may be substantially made of a fluorine-containing polymer material. That is, the binder particle group may be substantially made of a fluorine-containing polymer material.

The fluorine-containing polymer material may contain, for example, a structural unit derived from vinylidene fluoride (VdF). In this embodiment, a "structural unit" refers to an atomic group that constitutes a part of the basic structure of a polymer chain. The smallest structural unit that constitutes a regular molecular chain by its repetition is also called a "structural repeat unit".

The fluorine-containing polymer material may be, for example, a homopolymer. That is, the fluorine-containing polymer material may be, for example, polyvinylidene fluoride (PVdF). PVdF is substantially composed of repeating units derived from VdF.

The fluorine-containing polymer material may be, for example, a copolymer. That is, the fluorine-containing polymer material may contain a structural unit other than the structural unit derived from VdF. The fluorine-containing polymer material may contain, for example, a structural unit derived from tetrafluoroethylene (TFE) or a structural unit derived from hexafluoropropene (HFP). The copolymer may be, for example, a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

The molecular weight of the fluorine-containing polymer material can be measured, for example, by gel permeation chromatography (GPC). The polymer material may have a weight average molecular weight (standard polystyrene equivalent) of, for example, 100,000 to 2,000,000.

<All-solid-state battery>
2 is a conceptual diagram showing an all-solid-state battery in this embodiment. The all-solid-state battery 100 may include, for example, an exterior body (not shown). The exterior body may be, for example, a pouch made of a metal foil laminate film. The exterior body may house a power generating element 50. The power generating element 50 includes a positive electrode 10, a separator layer 30, and a negative electrode 20. That is, the all-solid-state battery 100 includes a positive electrode 10, a separator layer 30, and a negative electrode 20.

<Separator layer>
The separator layer 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator layer 30 separates the positive electrode 10 from the negative electrode 20. The separator layer 30 blocks the movement of electrons between the positive electrode 10 and the negative electrode 20. The separator layer 30 may have any thickness. The separator layer 30 may have a thickness of, for example, 1 to 100 μm. The separator layer 30 includes an electrolyte material. Details of the electrolyte material are as described above.

Positive pole
The positive electrode 10 may include a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector may include, for example, an aluminum (Al) foil. The positive electrode current collector may have a thickness of, for example, 5 to 50 μm.

The positive electrode active material layer may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer is in close contact with the separator layer 30. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer may further include a sulfide SE, a conductive material, a binder, and the like.

The positive electrode active material may be, for example, particulate. The positive electrode active material may have, for example, a D50 of 1 to 30 μm. The positive electrode active material may contain, for example, at least one selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , Li(NiCoMn)O ₂ , and Li(NiCoAl)O ₂ . For example, "(NiCoMn)" in "Li(NiCoMn)O ₂ " indicates that the sum of the composition ratios in the parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. The positive electrode active material may be surface-treated. A buffer layer may be formed on the surface of the positive electrode active material by the surface treatment. The buffer layer may contain, for example, lithium niobate (LiNbO ₃ ), etc. The buffer layer is expected to reduce the battery resistance.

Details of the sulfide SE are as described above. The amount of sulfide SE may be, for example, 1 to 100 parts by mass per 100 parts by mass of the positive electrode active material.

The conductive material may include, for example, vapor grown carbon fiber (VGCF) or the like. The binder may include, for example, PVdF or the like. The amount of the conductive material and binder particle group may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material.

The negative electrode 20 may include a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector may include, for example, copper (Cu) foil, nickel (Ni) foil, etc. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

The negative electrode active material layer may have a thickness of, for example, 10 to 200 μm. The negative electrode active material layer is in close contact with the separator layer 30. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer may further include a sulfide SE, a conductive material, a binder, and the like.

The negative electrode active material may be, for example, particulate. The negative electrode active material may have, for example, a D50 of 1 to 30 μm. The negative electrode active material may include, for example, at least one selected from the group consisting of graphite, Si, silicon oxide [SiO _x (0<x<2)], and lithium titanate.

Details of the sulfide SE are as described above. The amount of sulfide SE may be, for example, 1 to 100 parts by mass per 100 parts by mass of the negative electrode active material.

The conductive material may include, for example, VGCF. The binder particle group may include, for example, PVdF. The amount of the conductive material and the binder particle group may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material.

The present embodiment will be described below using examples, but the present embodiment is not limited to these.

《No. 1-1 to 1-5》
(Separator)
15LiI-10LiBr-75 (Li ₂ S-P ₂ S ₅ ) (glass ceramic type, D50 = 0.1 μm) was prepared as sulfide SE, butyl acetate was prepared as dispersion medium, and PVdF powder was prepared as binder particle group. More specifically, lithium phosphorus sulfide (Li ₂ S-P ₂ S ₅ ) in this example was "0.75Li ₂ S-0.25P ₂ S ₅ ."

A polypropylene (PP) container was prepared. The dispersion medium and binder particles were placed in the PP container so that the concentration of the binder particles was 5% by mass. A stirrer (Corning PC-420D) was placed in the PP container and the mixture was stirred for 12 hours. This resulted in the production of a polymer.

The polymer, sulfide SE, and dispersion medium were placed in a PP container so that the sulfide SE content was the value shown in Table 1. The above materials were stirred for 30 seconds using an ultrasonic dispersion device (UH-50, manufactured by SMT Corporation). After stirring, the PP container was placed in a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) and shaken for 3 minutes. This produced an electrolyte material.

A temporary support (Al foil) was prepared. The electrolyte material was applied to the surface of the temporary support using a doctor blade applicator. The electrolyte material was dried on a hot plate for 3 hours. The hot plate was set to a temperature of 130°C. As a result, a separator layer was formed on the surface of the temporary support.

(Test battery)
A positive electrode and a negative electrode were prepared. The separator, positive electrode, and negative electrode were punched into a disk shape. The separator had a diameter of 16 mm, and the positive electrode and negative electrode had a diameter of 19 mm. A 2032k type positive electrode can and a negative electrode can were prepared. The negative electrode, separator, positive electrode, SUS spacer, and SUS washer were stacked in this order between the negative electrode can and the positive electrode can from the negative electrode can toward the positive electrode can. After the placement, the coin batteries, which are test batteries No. 1-1 to 1-5, were prepared by pressing for 3 seconds with a coin press machine.

《No. 2-1 to 2-5》
Coin batteries, which were test batteries, were fabricated in the same manner as Nos. 1-1 to 1-5, except that the D50 of the sulfide SE was set to 0.5 μm.

《No. 3-1 to 3-5》
Coin batteries, which were test batteries, were produced in the same manner as Nos. 1-1 to 1-5, except that the D50 of the sulfide SE was set to 1.0 μm.

《No. 4-1 to 4-5》
Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was prepared. The above-mentioned polymer and LiTFSI were placed in a PP container so that the concentration of LiTFSI was 0.3 mass %. The above material was stirred for 30 seconds by the ultrasonic dispersion device. Thus, an electrolyte material was obtained.

A temporary support (Al foil) was prepared. The electrolyte material was applied to the surface of the temporary support using a doctor blade applicator and dried at room temperature for 12 hours. The electrolyte material was then dried on a hot plate for 3 hours. The hot plate was set to a temperature of 130°C. As a result, a separator layer was formed on the surface of the temporary support. Then, coin batteries, which were test batteries, were fabricated in the same manner as No. 1-1 to 1-5.

<Evaluation>
(Ionic Conductivity)
Each coin battery was left in a thermostatic bath set at 25°C for 3 hours. Then, AC impedance measurement was performed using an electrochemical measurement device (VMP3, manufactured by Biologic Co., Ltd.). The amplitude was 10 mV. The frequency range was 0.1 to 1.0 MHz. This resulted in a Cole-Cole plot. A circular arc was fitted to the Cole-Cole plot. The distance between the two intersections of the fitted circular arc and the real axis was determined. This distance was considered to be the "interface resistance." The reciprocal of the interface resistance was considered to be the ionic conductivity. The ionic conductivity of the coin battery No. 1-1 was taken as the reference (100), and the ionic conductivities of No. 2-1, 3-1, and 4-1 were relativized and evaluated. Similarly, the ionic conductivity of the coin battery No. 1-2 was taken as the reference (100), and the ionic conductivities of No. 2-2, 3-2, and 4-2 were taken as the reference (100). The ionic conductivity of the coin battery No. 1-3 was taken as the reference (100), and the ionic conductivity of the coin battery No. 2-3, 3-3, and 4-3 was relative to the ionic conductivity of the coin battery No. 1-4 as the reference (100), and the ionic conductivity of the coin battery No. 2-4, 3-4, and 4-4 was relative to the ionic conductivity of the coin battery No. 1-5, No. 2-3 to 2-5, No. 3-5, and No. 4-5 were evaluated by relative evaluation. The results are shown in Table 1. Note that the interface resistance of each of the coin batteries No. 1-5, No. 2-3 to 2-5, No. 3-5, and No. 4-5 was too large and exceeded the upper limit of measurement, so that the ionic conductivity could not be calculated.

Nos. 1-1 to 1-4 had high ionic conductivity. In addition, in No. 4-4, when the amount of sulfide SE exceeds a certain level, it becomes difficult to form contact points between the sulfide SE and the active material, resulting in a significant decrease in ionic conductivity, which is thought to be why the ionic conductivity appears to be high.

The present embodiment and the present examples are illustrative in all respects. The present embodiment and the present examples are not limiting. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, it is contemplated from the beginning that any configuration may be extracted from the present embodiment and the present examples and that they may be combined in any desired manner.

1 Sulfide solid electrolyte, 2 Polymer, 5 Electrolyte material, 10 Positive electrode, 20 Negative electrode, 30 Separator layer, 50 Power generating element, 100 All-solid-state battery.

Claims (1)

An electrolyte material comprising a sulfide solid electrolyte and a polymer,
The sulfide solid electrolyte has an average particle size of 0.1 μm or less,
The content of the sulfide solid electrolyte in the electrolyte material is 30% by volume or more and 80% by volume or less,
The sulfide solid electrolyte has the following formula (1):
vLiI-wLiBr-(100-vw) (Li ₂ S-P ₂ S ₅ ) (1)
having a composition represented by
In the above formula (1),
v represents the molar fraction percentage of the component derived from LiI, and satisfies the relationship of 10≦v≦20;
w represents the molar fraction percentage of the component derived from LiBr, and satisfies the relationship of 0≦w≦15;
(100-v-w) indicates the mole fraction percentage of the component derived from Li ₂ S-P ₂ S ₅ ,
The polymer includes a dispersion medium and a binder particle group,
The dispersion medium comprises butyl acetate,
The binder particles include polyvinylidene fluoride.

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