JP5682318B2 - All solid battery - Google Patents

Description

  The present invention relates to an all solid state battery having good input / output characteristics and contact interface resistance.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

  Since lithium batteries currently on the market use an electrolyte containing a flammable organic solvent, it is possible to install safety devices that suppress the temperature rise during short circuits and to improve the structure and materials to prevent short circuits. Necessary. On the other hand, an all-solid lithium battery in which the electrolyte is changed to a solid electrolyte layer to make the battery all solid does not use a flammable organic solvent in the battery. It is considered to be excellent in productivity.

  In such an all solid state battery, for example, as described in Patent Document 1, it is known to use graphite as a negative electrode active material. Graphite has the advantage of high charge / discharge capacity. Patent Document 2 discloses a solid battery (polymer electrolyte) using amorphous carbon (amorphous carbon) for the negative electrode active material layer. This is to improve the cycle durability of the secondary battery by suppressing the progress of the local battery reaction by using amorphous carbon as the high potential distribution active material.

JP 2009-176541 A JP 2007-026724 A

  In an all-solid-state battery, a negative electrode active material layer using only graphite can only insert and desorb conductive ions from only one direction, so there is a problem that input / output characteristics at high current density are low, In the negative electrode active material layer using only amorphous carbon, since amorphous carbon is not hardly crushed, there is a problem that the contact interface resistance with the solid electrolyte material is high. The present invention has been made in view of the above problems, and a main object of the present invention is to provide an all-solid battery having good input / output characteristics and contact interface resistance.

  In order to solve the above problems, in the present invention, a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and between the positive electrode active material layer and the negative electrode active material layer There is provided an all solid state battery having a solid electrolyte layer formed thereon, wherein the negative electrode active material layer contains graphite and amorphous carbon as the negative electrode active material.

  According to the present invention, since the negative electrode active material layer contains graphite and amorphous carbon as the negative electrode active material, an all-solid battery having favorable input / output characteristics and contact interface resistance can be obtained.

  In the said invention, it is preferable that the ratio of the said amorphous carbon with respect to the sum total of the said graphite and the said amorphous carbon exists in the range of 30 wt%-65 wt%. It is because it can be set as the all-solid-state battery excellent in the charge capacity in high current density.

  In the said invention, it is preferable that the said graphite is natural graphite or artificial graphite.

  In the above invention, the amorphous carbon is preferably soft carbon or hard carbon.

  In the present invention, there is an effect that it is possible to provide an all solid state battery having good input / output characteristics and contact interface resistance.

It is a schematic sectional drawing which shows an example of the electric power generation element of the all-solid-state battery of this invention. 3 is a SEM image of a negative electrode active material used in Comparative Example 1. 4 is a SEM image of a negative electrode active material used in Comparative Example 2. It is a graph which shows the measurement result of the charge capacity in the low current density of the all-solid-state battery obtained in Examples 1-4 and Comparative Examples 1 and 2. FIG. It is a graph which shows the measurement result of the charge capacity in the high current density of the all-solid-state battery obtained in Examples 1-4 and Comparative Examples 1 and 2. FIG. It is a graph which shows the evaluation result of the efficiency of the all-solid-state battery obtained in Examples 1-4 and Comparative Examples 1 and 2. FIG.

  Hereinafter, the all solid state battery of the present invention will be described in detail.

  The all solid state battery of the present invention includes a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid formed between the positive electrode active material layer and the negative electrode active material layer. An all-solid battery having an electrolyte layer, wherein the negative electrode active material layer contains graphite and amorphous carbon as the negative electrode active material.

  FIG. 1 is a schematic cross-sectional view showing an example of the power generation element of the all solid state battery of the present invention. 1 includes a positive electrode active material layer 1 containing a positive electrode active material, a negative electrode active material layer 2 containing a negative electrode active material, a positive electrode active material layer 1 and a negative electrode active material layer 2. And a solid electrolyte layer 3 formed therebetween. The present invention is characterized in that the negative electrode active material layer 2 contains graphite and amorphous carbon as the negative electrode active material.

According to the present invention, since the negative electrode active material layer contains graphite and amorphous carbon as the negative electrode active material, an all-solid battery having favorable input / output characteristics and contact interface resistance can be obtained. Amorphous carbon has lower crystallinity than graphite, and insertion and desorption of conductive ions (for example, Li ions) from multiple directions is possible, and the interlaminar spacing is wider than that of graphite. Is easy. For this reason, by using amorphous carbon, input / output characteristics at a high current density can be improved. On the other hand, graphite is softer than amorphous carbon and is advantageous for contact with a solid electrolyte material, so that contact interface resistance can be reduced. Graphite also has the advantage of a larger capacity per unit weight than amorphous carbon. Therefore, by mixing graphite and amorphous carbon and using them for the negative electrode active material, it is possible to obtain an all solid state battery that compensates for the above-mentioned disadvantages and has excellent input / output characteristics and contact interface resistance.
Hereinafter, the all solid state battery of the present invention will be described for each configuration.

1. Negative electrode active material layer First, the negative electrode active material layer in the present invention will be described. The negative electrode active material layer in the present invention is a layer containing at least a negative electrode active material, and may further contain at least one of a solid electrolyte material, a conductive material, and a binder as necessary.

  The negative electrode active material layer in the present invention contains graphite and amorphous carbon as the negative electrode active material. By using both graphite and amorphous carbon, both input / output characteristics and contact interface resistance can be improved.

  Examples of the graphite used in the present invention include natural graphite, artificial graphite, graphitized mesocarbon microbeads, etc. Among them, natural graphite and artificial graphite are preferable.

Examples of the shape of graphite include a particle shape. Specific examples include a spherical shape, a scale shape, a needle shape, a fiber shape, a lump shape, a layer shape, and the like. Among these, a spherical shape is preferable. When graphite has a particle shape, the average particle diameter (D ₅₀ ) is preferably in the range of 2 μm to 30 μm, for example.

  Examples of the amorphous carbon used in the present invention include hard carbon and soft carbon.

Examples of the shape of the amorphous carbon include a particle shape. Specifically, a spherical shape, a needle shape, a lump shape and the like can be mentioned, and among them, a spherical shape is preferable. When the amorphous carbon has a particle shape, the average particle diameter (D ₅₀ ) is preferably in the range of 1 μm to 20 μm, for example.

  The ratio of amorphous carbon to the total of graphite and amorphous carbon is not particularly limited as long as the effect of the present invention can be exhibited, but is preferably in the range of 30 wt% to 65 wt%, and 45 wt% to 55 wt%. % Is more preferable. It is because it can be set as the all-solid-state battery excellent in the charge capacity in a high current density by setting it as the said range. As described in Examples below, a negative electrode active material in which the amount of amorphous carbon in the negative electrode active material is 50 wt%, that is, 50 wt% graphite and 50 wt% amorphous carbon were used as the negative electrode active material. In this case, the charge capacity at a high current density is greatly improved as compared with any case where only graphite or amorphous carbon is used as the negative electrode active material. This is because, by containing equal amounts of graphite and amorphous carbon as the negative electrode active material, the gap between the hard and hard-to-crush amorphous carbon and the solid electrolyte material can be filled with soft and easy-to-crush graphite in a well-balanced state. As a result, it is considered that the contact between the negative electrode active material and the solid electrolyte material was improved.

  The content of the negative electrode active material in the negative electrode active material layer is, for example, preferably in the range of 10% by weight to 99% by weight, and more preferably in the range of 20% by weight to 90% by weight.

  The negative electrode active material layer in the present invention may further contain a solid electrolyte material. By adding the solid electrolyte material, the ion conductivity of the negative electrode active material layer can be improved. Examples of the solid electrolyte material include a sulfide solid electrolyte material and an oxide solid electrolyte material. The negative electrode active material layer may further contain a conductive material. By adding a conductive material, the conductivity of the negative electrode active material layer can be improved. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. The negative electrode active material layer may further contain a binder. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. Moreover, it is preferable that the thickness of a negative electrode active material layer exists in the range of 0.1 micrometer-1000 micrometers, for example.

2. Next, the positive electrode active material layer in the present invention will be described. The positive electrode active material layer in the present invention is a layer containing at least a positive electrode active material, and may further contain at least one of a solid electrolyte material, a conductive material and a binder as necessary.

As the positive electrode active material, is not particularly limited, for _{example, LiCoO 2, LiMnO 2, LiNiO} 2, LiVO 2, LiNi 1/3 Co 1/3 Mn 1/3 rock salt layered type active material such as _{O 2} And spinel type active materials such as LiMn ₂ O ₄ and Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine type active materials such as LiFePO ₄ and LiMnPO ₄ . Si-containing oxides such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ may be used as the positive electrode active material.

Examples of the shape of the positive electrode active material include a particle shape, and among them, a true spherical shape or an elliptical spherical shape is preferable. Moreover, when a positive electrode active material is a particle shape, it is preferable that the average particle diameter (D50) exists in the range of 0.1 micrometer- ₅₀ micrometers, for example.

In addition, an oxide coat layer is preferably formed on the surface of the positive electrode active material. It is because it can suppress that a positive electrode active material and solid electrolyte materials, such as sulfide solid electrolyte material, react, and a high resistance layer is formed, for example. In the present invention, the oxide is preferably an ion conductive oxide. It is because the resistance at the surface of the positive electrode active material can be lowered by ions conducting inside the ion conductive oxide. Thereby, a positive electrode active material layer with low interface resistance can be obtained. When the all solid state battery of the present invention is an all solid state lithium battery, the ion conductive oxide preferably includes a Li element, a M element (M is a metal element), and an O element. The M is not particularly limited, and examples thereof include Nb, Ti, and Zr. Furthermore, specific examples of such ion conductive oxides include LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , LiTiO ₃ , Li ₂ ZrO _{3 and the} like. On the other hand, the oxide may not have ionic conductivity. When such an oxide is used, the initial characteristic of the interface resistance cannot be improved, but the formation of the high resistance layer can be suppressed. Examples of the oxide having no ion conductivity include TiO ₂ and ZrO ₂ .

  The thickness of the coat layer is preferably in the range of 1 nm to 500 nm, for example, and more preferably in the range of 2 nm to 100 nm. This is because the reaction between the positive electrode active material and a solid electrolyte material such as a sulfide solid electrolyte material can be sufficiently suppressed within the above range. The coating layer preferably covers most of the surface of the positive electrode active material. Specifically, the coverage is preferably 40% or more, more preferably 70% or more, and 90% or more. More preferably. Examples of the method for forming the coat layer on the surface of the positive electrode active material include a rolling fluid coating method (sol-gel method), a mechanofusion method, a CVD method, and a PVD method. In addition, as a measuring method of the thickness of a coating layer, TEM etc. can be mentioned, for example, As a measuring method of the coverage of a coating layer, TEM, XPS, etc. can be mentioned, for example.

  The content of the positive electrode active material in the positive electrode active material layer is, for example, preferably in the range of 10% by weight to 99% by weight, and more preferably in the range of 20% by weight to 99% by weight. Note that the solid electrolyte material, the conductive material, and the binder used for the positive electrode active material layer are the same as those in the negative electrode active material layer described above. Moreover, it is preferable that the thickness of a positive electrode active material layer exists in the range of 0.1 micrometer-1000 micrometers, for example.

3. Next, the solid electrolyte layer in the present invention will be described. The solid electrolyte layer in the present invention is a layer formed between the positive electrode active material layer and the negative electrode active material layer, and is a layer composed of a solid electrolyte material.

  The solid electrolyte material included in the solid electrolyte layer is not particularly limited as long as it has ionic conductivity and insulating properties, and the same materials as those used in general all solid state batteries can be used. Examples thereof include a sulfide solid electrolyte material and an oxide solid electrolyte material. Among these, a sulfide solid electrolyte material is preferable in the present invention. It is because it can be set as the all-solid-state battery excellent in the output characteristic.

The sulfide solid electrolyte material used in the present invention is not particularly limited as long as it contains sulfur (S) and has ion conductivity and insulating properties. Here, when the all solid state battery of the present invention is an all solid state lithium battery, a raw material composition containing, for example, Li ₂ S and a sulfide of an element belonging to Group 13 to Group 15 as a sulfide solid electrolyte material. The thing which uses a thing can be mentioned.

Examples of the Group 13 to Group 15 elements include Al, Si, Ge, P, As, and Sb. Moreover, as a sulfide of an element of Group 13 to Group 15, specifically, Al ₂ S ₃ , SiS ₂ , GeS ₂ , P ₂ S ₃ , P ₂ S ₅ , As ₂ S ₃ , Sb ₂ S ₃ etc. can be mentioned. In particular, in the present invention, a sulfide solid electrolyte material using a raw material composition containing Li ₂ S and a sulfide of an element belonging to Group 13 to Group 15 is Li ₂ S—P ₂ S _5. The material is preferably a Li ₂ S—SiS ₂ material, a Li ₂ S—GeS ₂ material or a Li ₂ S—Al ₂ S ₃ material, and more preferably a Li ₂ S—P ₂ S ₅ material. This is because the Li ion conductivity is excellent.

  The sulfide solid electrolyte material used in the present invention may be sulfide glass, or may be crystallized sulfide glass obtained by heat-treating the sulfide glass. The sulfide glass can be obtained, for example, by subjecting the raw material composition to an amorphization method. Examples of the amorphization method include a mechanical milling method and a melt quenching method, and among them, the mechanical milling method is preferable. This is because processing at room temperature is possible, and the manufacturing process can be simplified. On the other hand, crystallized sulfide glass can be obtained, for example, by heat-treating sulfide glass at a temperature equal to or higher than the crystallization temperature. That is, a crystallized sulfide glass can be obtained by subjecting the raw material composition to an amorphization method and further a heat treatment.

Examples of the shape of the solid electrolyte material include a particle shape, and among them, a true spherical shape or an elliptical spherical shape is preferable. Moreover, when a solid electrolyte material is a particle shape, it is preferable that the average particle diameter (D50) exists in the range of 0.1 micrometer- ₅₀ micrometers, for example. The solid electrolyte material preferably has high Li ion conductivity, and the Li ion conductivity at room temperature is preferably 1 × 10 ⁻⁵ S / cm or more, for example, 1 × 10 ⁻⁴ S / cm. More preferably. The content of the solid electrolyte material in the solid electrolyte layer is not particularly limited as long as a desired insulating property can be obtained. For example, the content is in the range of 10% by weight to 100% by weight, especially 50% by weight. It is preferable to be within the range of ˜100% by weight.

  The solid electrolyte layer in the present invention may further contain a binder. This is because a solid electrolyte layer having flexibility can be obtained by containing a binder. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. In addition, the thickness of the solid electrolyte layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

4). Other Configurations The all solid state battery of the present invention has at least the negative electrode active material layer, the positive electrode active material layer, and the solid electrolyte layer described above. Furthermore, it usually has a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Among them, SUS is preferable. On the other hand, examples of the material for the negative electrode current collector include SUS, copper, nickel, and carbon. Among them, SUS is preferable. In addition, the thickness and shape of the positive electrode current collector and the negative electrode current collector are preferably appropriately selected according to the use of the all solid state battery. Moreover, the battery case of a general all-solid-state battery can be used for the battery case used for this invention. Examples of the battery case include a SUS battery case.

5. All-solid battery The all-solid battery of the present invention is preferably used for charging at a high current density. This is because a high charge capacity can be obtained. It is to be noted that the high current density, for ^example, in the range of ^{3mA / cm 2 ~60mA / cm 2} .

  Examples of the all-solid battery of the present invention include an all-solid lithium battery, an all-solid sodium battery, an all-solid magnesium battery, and an all-solid calcium battery. Of these, an all-solid lithium battery and an all-solid sodium battery are preferred. In particular, an all solid lithium battery is preferable. Further, the all solid state battery of the present invention may be a primary battery or a secondary battery, but among them, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as a vehicle-mounted battery. Examples of the shape of the all solid state battery of the present invention include a coin type, a laminate type, a cylindrical type, and a square type.

  Further, the method for producing the all solid state battery of the present invention is not particularly limited as long as it is a method capable of obtaining the above-described all solid state battery. Can be used. As an example of the manufacturing method of the all solid state battery, a power generation element is manufactured by sequentially pressing a material constituting the positive electrode active material layer, a material constituting the solid electrolyte layer, and a material constituting the negative electrode active material layer. Examples include a method in which the power generation element is housed in the battery case and the battery case is caulked.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  The present invention will be described more specifically with reference to the following examples.

[Example 1]
(Preparation of negative electrode active material)
As graphite and amorphous carbon, spherical natural graphite particles (average particle size 10.5 μm) and soft carbon particles (average particle size 11 μm) were prepared, respectively. 50 wt% of graphite and 50 wt% of amorphous carbon were mixed to obtain a negative electrode active material.

(Synthesis of solid electrolyte materials)
First, lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) were used as starting materials. These powders were weighed in a glove box under an Ar atmosphere (dew point −70 ° C.) so as to have a molar ratio of Li ₂ S: P ₂ S ₅ = 75: 25, mixed in an agate mortar, and a raw material composition Got. Next, 1 g of the obtained raw material composition was put into a 45 ml zirconia pot, and zirconia balls (Φ10 mm, 10 pieces) were further put in, and the pot was completely sealed (Ar atmosphere). The pot was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed at a base plate rotation speed of 370 rpm for 40 hours to obtain a solid electrolyte material (75Li ₂ S-25P ₂ S ₅ , sulfide glass).

(Production of all-solid battery)
First, the negative electrode active material and the solid electrolyte material were mixed at a weight ratio of negative electrode active material: solid electrolyte material = 63: 57 to obtain a negative electrode mixture. Next, LiCoO ₂ (positive electrode active material) whose surface was coated with LiNbO ₃ having a thickness of 7 nm and the above solid electrolyte material were mixed at a weight ratio of positive electrode active material: solid electrolyte material = 7: 3, and the positive electrode composite was mixed. I got the material. Using the obtained negative electrode mixture and positive electrode mixture, and the solid electrolyte material prepared as the solid electrolyte layer forming material, the power generation element 10 of the all-solid battery as shown in FIG. 1 was prepared. An all solid state battery was obtained using this power generation element.

[Example 2]
An all solid state battery was obtained in the same manner as in Example 1 except that in the production of the negative electrode active material, 75 wt% graphite and 25 wt% amorphous carbon were mixed.

[Example 3]
An all solid state battery was obtained in the same manner as in Example 1, except that 65 wt% graphite and 35 wt% amorphous carbon were mixed in the production of the negative electrode active material.

[Example 4]
An all-solid battery was obtained in the same manner as in Example 1, except that 30 wt% graphite and 70 wt% amorphous carbon were mixed in the production of the negative electrode active material.

[Comparative Example 1]
In the production of the negative electrode active material, an all solid state battery was obtained in the same manner as in Example 1 except that 100 wt% graphite was used.

[Comparative Example 2]
An all-solid battery was obtained in the same manner as in Example 1 except that 100 wt% amorphous carbon was used in the production of the negative electrode active material.

[Evaluation]
(Observation of negative electrode active material)
The negative electrode active materials used in Comparative Examples 1 and 2 were observed with a scanning electron microscope (SEM). The obtained SEM images are shown in FIGS. 2 and 3, respectively. As shown in FIG. 2, it was confirmed that particles were crushed and fell asleep only with graphite. Therefore, the graphite surfaces are aligned, and only insertion and desorption of conductive ions can be performed in one direction from the edge, which is disadvantageous for input / output at high current density that delivers a large amount of conductive ions in a short time. It is thought that it becomes. However, since graphite is soft and particles are easily crushed, it is considered to be advantageous for contact with a solid electrolyte material. On the other hand, as shown in FIG. 3, it was confirmed that particles were not crushed only with amorphous carbon. For this reason, insertion / extraction of conduction ions can be performed from multiple directions, which is considered advantageous for input / output at a high current density. However, since amorphous carbon is hard and particles are not easily crushed, it is considered disadvantageous for contact with the solid electrolyte material.

(Battery evaluation)
The all solid state batteries obtained in Examples 1 to 4 had better input / output characteristics and contact interface resistance than the all solid state batteries obtained in Comparative Examples 1 and 2. This is presumably because the use of graphite and amorphous carbon as the negative electrode active material enabled the contact interface resistance to be improved by graphite and the input / output characteristics to be improved by amorphous carbon. Moreover, charging / discharging was carried out at a low current density (0.293 mA / cm ² ) using the all solid state batteries obtained in Examples 1 to 4 and Comparative Examples 1 and ² , and a high current density (5.86 mA). / Cm < ² >). The voltage range was 2.5V to 4.2V. The measurement results of the charge capacity at low current density and high current density are shown in FIGS. As shown in FIG. 4 and Table 1, in charging at a low current density, when the amount of amorphous carbon in the negative electrode active material is 0 wt%, that is, the negative electrode active material is composed only of graphite, the charge capacity is the largest. It was. This is presumably because graphite has a higher capacity per weight of amorphous carbon than the capacity per weight of amorphous carbon. On the other hand, as shown in FIG. 5 and Table 1, in the charge at a high current density, the charge capacity was remarkably high when the amount of amorphous carbon in the negative electrode active material was 50 wt%. This is because the amount of graphite in the negative electrode active material and the amount of amorphous carbon are the same amount, so that the gap between the hard and easily crushed amorphous carbon and the solid electrolyte material can be filled with a soft and easily crushed graphite in a well-balanced manner. This is probably because the contact between the negative electrode active material and the solid electrolyte material was improved. In charging at a high current density, there is no constant relationship between the composition of the negative electrode active material and the charging capacity, and the charging capacity varies. Moreover, the evaluation result of the efficiency of the all-solid-state battery obtained in Examples 1-4 and Comparative Examples 1 and 2 is shown in FIG. The efficiency here refers to the ratio (B / A) of the charge capacity (B) at a high current density to the charge capacity (A) at a low current density. As shown in FIG. 6 and Table 1, it was confirmed that the lower the amount of amorphous carbon in the negative electrode active material, that is, the higher the amount of graphite in the negative electrode active material, the lower the efficiency. This is presumably because when graphite is charged at a high current density, the charge capacity of graphite is significantly reduced as compared with the case of charging at a low current density.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material layer 2 ... Negative electrode active material layer 3 ... Solid electrolyte layer 10 ... Electric power generation element of all-solid-state battery

Claims (3)

An all-solid battery having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer Because
The negative electrode active material layer contains graphite and amorphous carbon as the negative electrode active material,
The proportion of the amorphous carbon to the sum of the graphite and the amorphous carbon state, and are within the scope of 30wt% ~65wt%,
The solid solid electrolyte material contained in the electrolyte layer, all-solid-state battery, wherein a sulfide solid electrolyte material or an oxide solid electrolyte material der Rukoto.   The all-solid-state battery according to claim 1, wherein the graphite is natural graphite or artificial graphite. All-solid-state cell according to claim 1 or claim 2 wherein the amorphous carbon, characterized in that it is a soft carbon or hard carbon.