Negative electrode layer, method for manufacturing negative electrode layer, and all-solid battery

Abstract

The present disclosure provides a negative electrode layer having low resistance. The negative electrode layer is a negative electrode layer for a full-solid battery, and contains lithium titanate, a sulfide solid electrolyte, and a rubber-based binder. The proportion (A / B) of the adsorption amount (A) of the rubber-based binder adsorbed on the lithium titanate with respect to the total content (B) of the rubber-based binder contained in the negative electrode layer is 1.35% or less.

Description

Technical Field

[0001] This disclosure relates to a negative electrode layer, a method for manufacturing the negative electrode layer, and an all-solid-state battery. Background Technology

[0002] All-solid-state batteries are batteries with a solid electrolyte layer between the positive and negative electrode layers. Compared with liquid batteries with electrolytes containing flammable organic solvents, they have the advantage of being easier to simplify safety devices.

[0003] Titanium oxide is known as a negative electrode active material used in all-solid-state batteries. Titanium oxide exhibits minimal volume change during charge and discharge. For example, Japanese Patent Application Laid-Open No. 2021-128885 discloses a negative electrode for all-solid-state batteries comprising a negative electrode active material layer. This negative electrode active material layer comprises a first group of particles composed of titanium oxide and a second group of particles composed of a sulfide solid electrolyte. In the cross-section of the negative electrode active material layer, the contact interface length between the first and second particle groups is 3.77 mm or more. Summary of the Invention

[0004] From the perspective of high input / output efficiency in all-solid-state batteries, low resistance of the negative electrode layer is required. This disclosure provides a negative electrode layer with low resistance.

[0005] This disclosure provides a solution for a negative electrode layer in an all-solid-state battery. The negative electrode layer comprises lithium titanate, a sulfide solid electrolyte, and a rubber-based binder. The ratio (A / B) of the amount of the rubber-based binder adsorbed on the lithium titanate to the total content (B) of the rubber-based binder in the negative electrode layer is 1.35% or less.

[0006] According to this disclosure, the proportion of the amount of rubber-based adhesive adsorbed on lithium titanate is less than or equal to the total content of the rubber-based adhesive contained in the negative electrode layer, thus resulting in a negative electrode layer with low resistance.

[0007] In the above disclosure, the rubber-based adhesive may also contain styrene-butadiene rubber.

[0008] In the above disclosure, the lithium titanate of the negative electrode layer may also be composed of Li4Ti5O. 12 The components of the representation.

[0009] In the above disclosure, the proportion of the rubber-based adhesive in the negative electrode layer may be 1% or more and 20% or less by volume. The proportion of lithium titanate in the negative electrode layer may be 20% or more and 80% or less by volume. The proportion of the sulfide solid electrolyte in the negative electrode layer may be 15% or more and 75% or less by volume.

[0010] Additionally, one aspect of this disclosure is a method for manufacturing a negative electrode layer for an all-solid-state battery, comprising the following steps: preparing a dispersion obtained by dispersing a sulfide solid electrolyte and a first component in a dispersion medium; adding a second component to the dispersion and dispersing it to obtain a negative electrode paste; and applying the negative electrode paste and drying it to form a negative electrode layer. One of the first component and the aforementioned second component is lithium titanate, and the other is a rubber-based adhesive.

[0011] According to this disclosure, a dispersion is prepared by dispersing a sulfide solid electrolyte in a dispersion medium. A rubber-based binder and lithium titanate are added during the preparation of the dispersion and subsequently when obtaining the negative electrode paste from the dispersion. As a result, the rubber-based binder preferentially adsorbs onto the sulfide solid electrolyte, thus enabling the fabrication of a negative electrode layer with low resistance.

[0012] In the above disclosure, the first component may also be the lithium titanate, and the second component may also be the rubber-based adhesive.

[0013] In the above disclosure, the process of preparing the dispersion may also include the following steps: adding the first component to the dispersion medium and performing a first dispersion treatment to obtain a precursor dispersion; adding the sulfide solid electrolyte to the precursor dispersion and performing a second dispersion treatment to obtain the dispersion.

[0014] In addition, one aspect of this disclosure is an all-solid-state battery having a positive electrode layer, the aforementioned negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer.

[0015] According to this disclosure, a low-resistance all-solid-state battery is formed by using the aforementioned negative electrode layer.

[0016] In this disclosure, a negative electrode layer with low resistance can be provided. Attached Figure Description

[0017] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings, wherein the same reference numerals denote the same elements.

[0018] Figure 1 This is a flowchart illustrating an example of a method for manufacturing the negative electrode layer of this disclosure.

[0019] Figure 2 This is a schematic cross-sectional view showing an example of an all-solid-state battery of this disclosure.

[0020] Figure 3 This is a flowchart illustrating an example of a method for manufacturing the negative electrode layer in a comparative example.

[0021] Figure 4A This is an SEM image of the cross-section of the negative electrode layer of the evaluation battery obtained in the embodiment.

[0022] Figure 4B This is a carbon mapping image (C image) of the negative electrode layer cross-section of the battery obtained in the examples.

[0023] Figure 4C This is a sulfur mapping image (S-image) of the cross-section of the negative electrode layer of the battery used for evaluation, obtained in the examples.

[0024] Figure 4D The image shows a mapping of sulfur and osmium (S, Os image) of the cross-section of the negative electrode layer of the battery obtained in the examples.

[0025] Figure 5A The image shows a mapping of sulfur and osmium (S, Os image) of the cross-section of the negative electrode layer of the battery obtained in the examples.

[0026] Figure 5B This is achieved by coloring the areas where Os and S elements exist red, and coloring the other areas black. Figure 5A The image after the mapping image is separated.

[0027] Figure 5C From Figure 5B The image shows the Os element extracted from lithium titanate.

[0028] Figure 6A This is an SEM image of the cross-section of the negative electrode layer of the evaluation battery obtained in the embodiment.

[0029] Figure 6B The image shows a mapping of sulfur and osmium (S, Os image) of the cross-section of the negative electrode layer of the battery obtained in the examples.

[0030] Figure 6C This is an extracted image of Os elements adsorbed on lithium titanate in the cross-section of the negative electrode layer of the evaluation battery obtained in the examples.

[0031] Figure 6D This is a SEM image of the cross-section of the negative electrode layer of the evaluation battery obtained in the comparative example.

[0032] Figure 6E The images shown are mapping images (S, Os images) of sulfur and osmium in the cross-section of the negative electrode layer of the battery obtained in the comparative example.

[0033] Figure 6F This is an extracted image of the Os element on the cross-section of the negative electrode layer of the evaluation battery obtained in the comparative example. Detailed Implementation

[0034] The following provides a detailed description of the negative electrode layer, the method for manufacturing the negative electrode layer, and the all-solid-state battery disclosed herein.

[0035] A. Negative electrode layer

[0036] The negative electrode layer of this disclosure comprises lithium titanate, a sulfide solid electrolyte, and a rubber-based binder. The ratio (A / B) of the amount of the rubber-based binder adsorbed on the lithium titanate to the total content (B) of the rubber-based binder contained in the negative electrode layer is 1.35% or less. Furthermore, the negative electrode layer of this disclosure is used in all-solid-state batteries.

[0037] According to this disclosure, the proportion of the amount of rubber-based adhesive adsorbed on lithium titanate relative to the total content of the rubber-based adhesive contained in the negative electrode layer is below a predetermined value, thus resulting in a negative electrode layer with low resistance. As described above, in the case of a negative electrode layer containing lithium titanate and rubber-based adhesive, lithium titanate has a high affinity for the rubber-based adhesive. Therefore, the rubber-based adhesive is easily adsorbed onto the lithium titanate. If the surface of the lithium titanate is covered by the rubber-based adhesive, the reaction area of ​​the lithium titanate as an active material is reduced, thus resulting in high resistance of the negative electrode layer.

[0038] For example, silicon-based particles are known as negative electrode active materials for batteries. Silicon-based particles have a lower affinity for rubber-based adhesives than lithium titanate does for rubber-based adhesives. Therefore, when using silicon-based particles as the negative electrode layer, the likelihood of high resistivity problems caused by the easy adsorption of adhesives onto the negative electrode active material is low.

[0039] Furthermore, fluoride-based binders such as polyvinylidene fluoride (PVDF) exhibit low dispersibility in dispersion media used with sulfide solid electrolytes. Therefore, fluoride-based binders tend to aggregate within the negative electrode layer. When using such fluoride-based binders as the negative electrode layer, the likelihood of high resistivity issues arising from the binder's tendency to adsorb onto the negative electrode active material is low.

[0040] Thus, the high resistivity problem of the negative electrode layer is particularly significant in negative electrode layers using lithium titanate as the negative electrode active material and rubber-based binders as the binder. In response, the negative electrode layer of this disclosure has a proportion of rubber-based binder adsorbed on the lithium titanate that is less than or equal to the total content of the rubber-based binder in the negative electrode layer. Therefore, the decrease in the reaction area of ​​lithium titanate can be suppressed, and the resistance of the negative electrode layer can be reduced.

[0041] 1. Rubber-based adhesives

[0042] The negative electrode layer of this disclosure has a rubber-based binder. In this disclosure, the ratio (A / B) of the amount of rubber-based binder adsorbed on the lithium titanate to the total content B of the rubber-based binder contained in the negative electrode layer is typically 1.35% or less, and may also be 1.0% or less. When the above ratio (A / B) is large, the reaction area of ​​the lithium titanate decreases, resulting in high resistivity. On the other hand, the above ratio (A / B) is, for example, 0% or more, and may also be 0.5% or more. The above ratio (A / B) is determined by the following sequence.

[0043] (Electrode staining)

[0044] Under an inert atmosphere such as a glove box, at least part of the outer casing of the all-solid-state battery is peeled off to expose the power generation element. The all-solid-state battery with the power generation element exposed is placed in a chamber not exposed to the atmosphere and transferred to a vacuum electronic staining apparatus. For example, a VSC4TWDH (manufactured by Filgen Co., Ltd.) can be used as the vacuum electronic staining apparatus. After creating a vacuum atmosphere inside the vacuum electronic staining apparatus, the chamber is opened, and osmium tetroxide (OsO4) gas is introduced. Osmium (Os) staining is performed by adjusting the staining time and gas concentration. Osmium tetroxide (OsO4) reacts with the double bonds of the rubber-based adhesive and adsorbs onto the rubber-based adhesive.

[0045] (Production of the experimental film)

[0046] The osmium-stained power generation element is cut to an appropriate size under an inert atmosphere. This produces a test piece of the power generation element. The cut section of the test piece is then machined using an ion milling apparatus, such as a grinding frame not exposed to the atmosphere. For example, an ion milling apparatus "IM4000PLUS" (or equivalent) manufactured by Hitachi High-Tech Corporation can be used. The cross-section machining is performed under a vacuum or inert atmosphere. During the cross-section machining, the test piece can be cooled.

[0047] (Image Acquisition)

[0048] After cross-section processing, the specimen is introduced into a field emission scanning electron microscope (FE-SEM). For example, the FE-SEM "Regulus 8230" (or equivalent) manufactured by Hitachi High Technology Co., Ltd. is used. During the process from cross-section processing to introduction into the SEM, a vacuum atmosphere is maintained to prevent the specimen from being exposed to the atmosphere.

[0049] The cross-section of the negative electrode layer of the test piece was observed using FE-SEM. Furthermore, the observation position for the negative electrode layer cross-section was preferably a location where conductive material was not observed. This allows for accurate calculation of the total content B of the rubber-based adhesive. At the observation position, secondary electron imaging and reflected electron imaging were performed using SEM. The magnification was, for example, 5000x. At the same observation position, mapping images of carbon (C), sulfur (S), and sulfur (S) and osmium (Os) were obtained using EDX (Energy Dispersive X-ray Spectroscopy). The above observations were preferably performed at multiple locations. In this case, for example, six observation positions were set at approximately equal intervals in a plane parallel to the negative electrode current collector, i.e., in a direction orthogonal to the thickness direction of the negative electrode layer.

[0050] (Image Analysis)

[0051] Using the images obtained above, (1) the total content B of the rubber-based adhesive was determined, and (2) the amount A of the rubber-based adhesive adsorbed on lithium titanate was determined.

[0052] (1) Determination of the total content B of rubber-based adhesives

[0053] First, the carbon mapping image is binarized, and the number of pixels P1 in the extracted C element image is counted. The carbon mapping image, as the name suggests, is an image that maps the presence of carbon. In image processing, the carbon mapping image is equivalent to a simple image, therefore the number of pixels P1 can be counted accurately using known binarization methods. The binarization threshold can be set by considering at least one of the volume ratios of lithium titanate, conductive materials, and rubber-based adhesives.

[0054] Next, the sulfur mapping image is binarized, and the number of pixels P2 in the extracted S element image is counted. The sulfur mapping image, as the name suggests, is an image that maps the presence of sulfur. In image processing, the sulfur mapping image is equivalent to a simple image, therefore the number of pixels P2 can be counted accurately using known binarization processing. The binarization threshold can be set, for example, by considering at least one of the volume ratio of lithium titanate and the volume ratio of the sulfide solid electrolyte.

[0055] Next, the number of pixels P3, obtained by subtracting P2 from P1, is calculated. In this disclosure, P3 is defined as the total content B of the rubber-based adhesive. Furthermore, in the carbon mapping image, in addition to the shape of the sulfide solid electrolyte, the shape of lithium titanate is also observed. The shape of lithium titanate observed in the carbon mapping image is caused by the surface functional groups and solvent residues of lithium titanate. Both the surface functional groups and solvent residues of lithium titanate are present in small amounts. Therefore, P3 can be defined as the total content B of the rubber-based adhesive.

[0056] (2) Determination of the adsorption amount A of rubber-based adhesives adsorbed on lithium titanate

[0057] The mapping images of osmium (Os) and sulfur (S) were separated into regions where Os and S elements were present, as well as other regions. Next, large blocks (S elements in the sulfide solid electrolyte and Os elements covering the S elements in the sulfide solid electrolyte) were removed. Thus, the residual Os elements, i.e., the Os elements adsorbed on lithium titanate, were extracted. The number of pixels P4 in the extracted Os element image was counted.

[0058] Divide the number of pixels P4 obtained in (2) above by the number of pixels P3 obtained in (1) above, and express it as a percentage ((P4 / P3)×100(%)). From this, calculate the above ratio (A / B). In addition, when observing at multiple locations (e.g., 6 locations), calculate ((P4 / P3)×100(%)) for each observation location, and use their average as the above ratio (A / B).

[0059] (Rubber-based adhesives)

[0060] As the rubber-based adhesive disclosed herein, any known rubber-based adhesive suitable for use as an adhesive in all-solid-state batteries can be used. Examples of rubbers included in the rubber-based adhesive include butadiene rubber, hydrogenated butadiene rubber, styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, and ethylene propylene rubber. Among these, styrene-butadiene rubber (SBR) is preferred.

[0061] The proportion of rubber-based adhesive in the negative electrode layer is, for example, more than 1% by volume and less than 20% by volume, or more than 5% by volume and less than 20% by volume.

[0062] 2. Lithium titanate

[0063] The negative electrode layer disclosed herein contains lithium titanate. Lithium titanate functions as the active material of the negative electrode layer.

[0064] Lithium titanate (LTO) is a compound containing Li, Ti, and O. Some of the Ti in lithium titanate can be replaced by other metal elements (e.g., transition metals). Similarly, some of the Li in lithium titanate can be replaced by other metal elements (e.g., alkali metals). Lithium titanate can also have a spinel-structured crystal phase.

[0065] Examples of components of lithium titanate include Li. x Ti y O z (3.5≤x≤4.5, 4.5≤y≤5.5, 11≤z≤13). x can be 3.7 or higher and 4.3 or lower, or 3.9 or higher and 4.1 or lower. y can be 4.7 or higher and 5.3 or lower, or 4.9 or higher and 5.1 or lower. z can be 11.5 or higher and 12.5 or higher, or 11.7 or higher and 12.3 or lower. Lithium titanate preferably has a composition of Li4Ti5O. 12 The components of the representation.

[0066] Lithium titanate can be shaped, for example, into granular form. The average particle size (D) of lithium titanate... 50 For example, it can be 10 nm or larger and 50 μm or smaller, or 100 nm or larger and 20 μm or smaller. Average particle size (D) 50 The median diameter (CM) refers to the cumulative 50% of the particle size distribution, which can be calculated, for example, by a laser diffraction particle size analyzer or a scanning electron microscope (SEM).

[0067] The specific surface area of ​​lithium titanate is, for example, 2 m². 2 / g or more and 10m 2 Below / g, it can be 3m 2 / g or more and 8m 2 Below / g, it can also be 3.9m 2 / g or more and 6.5m 2 / g or less. Specific surface area is calculated, for example, by gas adsorption methods such as the BET method.

[0068] Lithium titanate preferably exhibits good electronic conductivity through Li insertion. The electronic conductivity of lithium titanate in the Li-inserted state (25°C) is, for example, 8.0 × 10⁻⁶. -1 S / cm or higher.

[0069] The proportion of lithium titanate in the negative electrode layer can be, for example, 20% or more and 80% or less, 30% or more and 70% or less, or 40% or more and 65% or less. If the proportion of lithium titanate is low, the volumetric energy density may become low. On the other hand, if the proportion of lithium titanate is high, the ion conduction pathway may not be sufficiently formed.

[0070] 3. Sulfide solid electrolyte

[0071] The negative electrode layer of the present disclosure contains a sulfide solid electrolyte. The sulfide solid electrolyte constitutes an ion conduction path in the negative electrode layer. The sulfide solid electrolyte generally contains sulfur (S) as the main component of the anion element. The sulfide solid electrolyte contains, for example, Li, A (A is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S. A preferably contains at least P. In addition, the sulfide solid electrolyte may also contain at least one of Cl, Br, and I as a halogen. In addition, the sulfide solid electrolyte may also contain O.

[0072] The sulfide solid electrolyte can be a glassy sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. In addition, when the sulfide solid electrolyte has a crystal phase, examples of the crystal phase include a Thio-LISICON type crystal phase, an LGPS type crystal phase, and an argyrodite type crystal phase.

[0073] The composition of the sulfide solid electrolyte is not particularly limited, and examples thereof include xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30).

[0074] The sulfide solid electrolyte may have a composition represented by the general formula Li 4-x Ge 1-x P x S4 (0 < x < 1). In the above general formula, at least part of Ge can be replaced by at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, at least part of P can be replaced by at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, part of Li can be replaced by at least one of Na, K, Mg, Ca, and Zn. In the above general formula, part of S can be replaced by a halogen (at least one of F, Cl, Br, and I).

[0075] As other compositions of the sulfide solid electrolyte, examples thereof include Li 7-x-2y PS 6-x-y X y 、Li 8-x-2y SiS 6-x- y X y 、Li 8-x-2y GeS 6-x-y X yIn these compositions, X is at least one of F, Cl, Br, and I, and x and y satisfy 0 ≤ x and 0 ≤ y.

[0076] Sulfide solid electrolytes preferably possess high Li-ion conductivity. For example, the Li-ion conductivity of a sulfide solid electrolyte at 25°C is 1 × 10⁻⁶. -4 S / cm or higher, preferably 1×10 -3 S / cm or higher. Sulfide solid electrolytes are preferably those with high insulation properties. The electronic conductivity of sulfide solid electrolytes at 25°C is, for example, 10. -6 For values ​​below S / cm, it can be 10. -8 Below S / cm, it can also be 10. -10 S / cm or less. Furthermore, granular form is an example of a sulfide solid electrolyte. The average particle size (D) of the sulfide solid electrolyte is... 50 For example, 0.1 μm or larger and 50 μm or smaller.

[0077] The proportion of sulfide solid electrolyte in the negative electrode layer is, for example, 15% or more and 75% or less by volume, or 15% or more and 60% or less by volume. If the proportion of sulfide solid electrolyte is low, sufficient ion conduction pathways may not be formed. On the other hand, if the proportion of sulfide solid electrolyte is high, the volumetric energy density may decrease.

[0078] 4. Negative electrode layer

[0079] The negative electrode layer of this disclosure may or may not contain a conductive material. In this disclosure, "conductive material" refers to a material with a higher electronic conductivity than lithium titanate (strictly speaking, the electronic conductivity of lithium titanate in the Li-intercalated state). Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include granular carbon materials such as acetylene black (AB) and Ketjen black (KB), as well as fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). The proportion of the conductive material in the negative electrode layer is, for example, 0.1% by volume or more and 10% by volume or less, or 0.3% by volume or more and 10% by volume or less. On the other hand, when the negative electrode layer does not contain a conductive material, lithium titanate is preferably the material with the highest electronic conductivity in the negative electrode layer.

[0080] In addition, the thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0081] B. Manufacturing method of negative electrode layer

[0082] Figure 1 This is a flowchart illustrating an example of a method for manufacturing the negative electrode layer of this disclosure. Figure 1In the manufacturing method shown, firstly, a dispersion in which a sulfide solid electrolyte and a first component are dispersed in a dispersion medium is prepared (dispersion preparation step). Next, a second component is added to the dispersion and dispersed to obtain a negative electrode paste (addition step). Here, one of the first and second components is lithium titanate, and the other is a rubber-based adhesive. Next, the negative electrode paste is applied and dried, thereby forming a negative electrode layer (negative electrode layer formation step).

[0083] Rubber-based binders have a slightly higher affinity for sulfide solid electrolytes than for lithium titanate, but the affinity is roughly the same. Therefore, during the manufacturing process of the negative electrode paste, if lithium titanate and rubber-based binders come into contact in the absence of sulfide solid electrolytes, the amount of rubber-based binder adsorbed on the lithium titanate increases.

[0084] On the other hand, the method for manufacturing the negative electrode layer disclosed herein includes a dispersion preparation step, in which a dispersion is prepared in which at least a sulfide solid electrolyte is dispersed in a dispersion medium. In this dispersion preparation step and the subsequent addition step, a rubber-based binder and lithium titanate are added, respectively. As a result, contact between lithium titanate and the rubber-based binder in the absence of the sulfide solid electrolyte can be avoided, and the rubber-based binder preferentially coats the sulfide solid electrolyte. Therefore, the amount of rubber-based binder covering the lithium titanate can be reduced.

[0085] In this disclosure, the first component is preferably lithium titanate, and the second component is a rubber-based adhesive. Alternatively, the first component may be a rubber-based adhesive, and the second component may be lithium titanate.

[0086] 1. Dispersion preparation process

[0087] The dispersion preparation step is a step of preparing a dispersion obtained by dispersing the sulfide solid electrolyte and the first component in a dispersion medium. The first component is lithium titanate or a rubber-based binder. Lithium titanate is preferred as the first component. The sulfide solid electrolyte, lithium titanate, and rubber-based binder are the same as described in "A. Negative Electrode Layer" above, and therefore will not be described further here.

[0088] The dispersion medium disclosed herein imparts fluidity to the dispersion. Furthermore, the dispersion medium can also dissolve a portion of the sulfide solid electrolyte and a portion of the first component. Examples of dispersion media include esters such as butyl butyrate, dibutyl ether, and ethyl acetate; ketones such as diisobutyl ketone (DIBK), methyl ketones, and methyl propyl ketone; aromatic hydrocarbons such as xylene, benzene, and toluene; alkanes such as heptane, dimethylbutane, and methylhexane; and amines such as tributylamine and allylamine. The concentration of the solid component in the dispersion is, for example, 30% by weight or more and 80% by weight or less, or 50% by weight or more and 70% by weight or less.

[0089] The method for manufacturing the dispersion disclosed herein is not particularly limited. One example of the method for manufacturing the dispersion includes a step of obtaining a precursor dispersion and a step of obtaining the dispersion. In the step of obtaining the precursor dispersion, for example… Figure 1 As shown, by adding a first component ( Figure 1 The precursor dispersion is obtained by first dispersing lithium titanate (in the form of lithium titanate). In the process of obtaining the dispersion, a sulfide solid electrolyte is added to the precursor dispersion and a second dispersion treatment is performed to obtain the dispersion.

[0090] On the other hand, although not illustrated, another example of a method for producing a dispersion may include: a step of obtaining a precursor dispersion by adding a sulfide solid electrolyte to a dispersion medium and performing a first dispersion treatment; and a step of obtaining a dispersion by adding a first component to the precursor dispersion and performing a second dispersion treatment. Furthermore, yet another example of a method for producing a dispersion may include the following step: obtaining a dispersion by adding both a first component and a sulfide solid electrolyte to a dispersion medium and performing a dispersion treatment.

[0091] The dispersion process can employ well-known and suitable methods. As an example of a dispersion process, the use of an ultrasonic homogenizer can be cited. Furthermore, the dispersion conditions are preferably adjusted appropriately to obtain the desired dispersion.

[0092] In this disclosure, a conductive material may be added during the dispersion preparation process. The conductive material may be added simultaneously with the first component, simultaneously with the sulfide solid electrolyte, or simultaneously with both the first component and the sulfide solid electrolyte. Alternatively, it may be added separately with the first component and the sulfide solid electrolyte.

[0093] 2. Add process

[0094] The addition step involves adding a second component to the dispersion prepared in "1. Dispersion Preparation Step" above and dispersing it to obtain a negative electrode paste. The second component is lithium titanate or a rubber-based binder. The second component is preferably a rubber-based binder.

[0095] The method for distributed processing is the same as described above, and therefore is omitted here.

[0096] In this disclosure, a conductive material can be added during the addition process. In this case, the conductive material and the second component can be added simultaneously, or the conductive material can be added first and then the second component, or vice versa.

[0097] 3. Negative electrode layer formation process

[0098] The negative electrode layer formation process involves applying the negative electrode paste obtained in "2. Addition Process" above and allowing it to dry to form the negative electrode layer. Preferably, the negative electrode paste is applied to the current collector. The application method is not particularly limited, and any known suitable application method can be used. Furthermore, the negative electrode layer produced through the above processes is the same as described in "A. Negative Electrode Layer" above, and therefore will not be described here.

[0099] C. All-solid-state batteries

[0100] Figure 2 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Figure 2 The all-solid-state battery 10 shown includes: a positive electrode layer 1, a negative electrode layer 2, a solid electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive current collector 4 for collecting current in the positive electrode layer 1, and a negative current collector 5 for collecting current in the negative electrode layer 2. In this disclosure, the negative electrode layer 2 is the negative electrode layer described in "A. Negative Electrode Layer" above.

[0101] According to this disclosure, a low-resistance all-solid-state battery is formed by using the above-described negative electrode layer.

[0102] 1. Negative electrode layer

[0103] Regarding the negative electrode layer of this disclosure, the content is the same as that described in "A. Negative Electrode Layer" above, so it is omitted here.

[0104] 2. Positive electrode layer

[0105] The positive electrode layer of this disclosure contains at least a positive electrode active material. Depending on the need, the positive electrode layer of this disclosure may further contain at least one of a solid electrolyte, a conductive material, and a binder. Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered active substances in rock salt, LiMn2O4, Li4Ti5O 12 and Li(Ni 0.5 Mn 1.5 Spinel-type active materials such as LiNbO4, olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are preferred. It is preferable to coat the surface of the positive electrode active material with an ion-conducting oxide. This is because it can suppress the formation of a high-resistivity layer due to the reaction between the positive electrode active material and the solid electrolyte (especially a sulfide solid electrolyte). Examples of ion-conducting oxides include LiNbO3. The thickness of the ion-conducting oxide is, for example, 1 nm or more and 30 nm or less.

[0106] The proportion of the positive electrode active material in the positive electrode layer can be, for example, 20% or more by volume, 30% or more by volume, or 40% or more by volume. If the proportion of the positive electrode active material is low, the volumetric energy density may decrease. On the other hand, the proportion of the positive electrode active material can be, for example, 80% or less by volume, 70% or less by volume, or 60% or less by volume. If the proportion of the positive electrode active material is high, it may be impossible to fully form ion conduction pathways and electron conduction pathways.

[0107] There are no particular limitations on the solid electrolyte; for example, sulfide solid electrolytes can be cited. Details regarding sulfide solid electrolytes are the same as those described in "A. Negative Electrode Layer" above. Regarding conductive materials and binders, the details are the same as those described in "A. Negative Electrode Layer". Furthermore, the thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0108] 3. Solid electrolyte layer

[0109] The solid electrolyte layer of this disclosure is disposed between the aforementioned positive electrode layer and the aforementioned negative electrode layer. The solid electrolyte layer contains at least a solid electrolyte and may also contain a binder. The contents regarding the solid electrolyte and binder are the same as described in "2. Positive Electrode Layer," and therefore are omitted here. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0110] 4. All-solid-state batteries

[0111] In this disclosure, "all-solid-state battery" refers to a battery having a solid electrolyte layer (at least a layer containing a solid electrolyte). Furthermore, the all-solid-state battery of this disclosure includes a power generation element, which has a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The power generation element typically has a positive current collector and a negative current collector. The positive current collector is, for example, disposed on the surface of the positive electrode layer opposite to the solid electrolyte layer. Examples of materials for the positive current collector include metals such as aluminum, SUS, and nickel. Examples of shapes for the positive current collector include foil and mesh. On the other hand, the negative current collector is, for example, disposed on the surface of the negative electrode layer opposite to the solid electrolyte layer. Examples of materials for the negative current collector include metals such as copper, SUS, and nickel. Examples of shapes for the negative current collector include foil and mesh.

[0112] The all-solid-state battery of this disclosure can include an outer casing that houses the aforementioned power generation element. Examples of such outer casings include laminated casings and shell-type casings. Furthermore, the all-solid-state battery of this disclosure can also include a constraint clamp that applies a constraint pressure in the thickness direction to the aforementioned power generation element. Known clamps can be used as the constraint clamp. The constraint pressure can be, for example, 0.1 MPa or more and 50 MPa or less, or 1 MPa or more and 20 MPa or less. If the constraint pressure is low, it may be impossible to form a good ion conduction path and a good electron conduction path. On the other hand, if the constraint pressure is high, the constraint clamp becomes larger, and the volumetric energy density of the all-solid-state battery may decrease.

[0113] The type of all-solid-state battery disclosed herein is not particularly limited, but lithium-ion secondary batteries are typical. The applications of all-solid-state batteries are not particularly limited; examples include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred for use as power sources for driving hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. Furthermore, the all-solid-state battery disclosed herein can be used as a power source for mobile bodies other than vehicles (e.g., railways, ships, and aircraft), and also as a power source for electronic devices such as information processing devices.

[0114] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any technical solutions having a structure that is substantially the same as the technical concept described in the claims of this disclosure and achieving the same effect are included within the technical scope of this disclosure.

[0115] [Example]

[0116] (Making of negative electrode paste)

[0117] Weigh the Li4Ti5O as the negative electrode active material. 12 Particles (LTO, density 3.5 g / cc), conductive material (VGCF, density 2 g / cc), binder (SBR, density 0.9 g / cc), dispersion medium (butyl butyrate), sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5 series glass ceramic, density 2 g / cc).

[0118] according to Figure 1The flowchart shown illustrates the preparation of the negative electrode paste. First, LTO particles are added to the dispersion medium, and a first dispersion treatment is performed using an ultrasonic homogenizer (SMT UH-50), thereby obtaining a precursor dispersion. Next, the sulfide solid electrolyte is added to the obtained precursor dispersion, and a second dispersion treatment is performed using an ultrasonic homogenizer (SMT UH-50), thereby obtaining a dispersion. Then, the binder is added to the dispersion, and dispersion is performed using an ultrasonic homogenizer (SMT UH-50), resulting in the negative electrode paste.

[0119] (Making the positive electrode paste)

[0120] As the positive electrode active material, LiNi with LiNbO3 surface treatment was used. 1 / 3 Co 1 / 3 Mn 1 / 3 O2. Weigh the positive electrode active material, conductive material (VGCF), sulfide solid electrolyte, binder (SBR), and dispersion medium (butyl butyrate), and mix them using an ultrasonic homogenizer (SMT UH-50). This yields the positive electrode paste.

[0121] (Preparation of the SE layer paste)

[0122] In a polypropylene container, a dispersion medium (heptane), a binder (a heptane solution containing 5% by mass of butadiene rubber-based binder), and a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5-based glass-ceramic with an average particle size D) are added. 50 The sample (2.5 μm) was mixed for 30 seconds using an ultrasonic homogenizer (SMT UH-50). Then, the container was vibrated for 3 minutes. This yielded a paste for the solid electrolyte layer (SE layer).

[0123] (The fabrication of an all-solid-state battery)

[0124] First, a positive electrode paste is applied to the positive current collector (aluminum foil) using a scraper method with a coating tool. After application, it is dried on a heating plate at 100°C for 30 minutes. This yields a positive electrode having a positive current collector and a positive electrode layer. Next, a negative electrode paste is applied to the negative current collector (copper foil). After application, it is dried on a heating plate at 100°C for 30 minutes. This yields a negative electrode having a negative current collector and a negative electrode layer. Here, while maintaining a specific charge capacity of 185 mAh / g for the positive electrode, the weight per unit area of ​​the negative electrode layer is adjusted to increase the specific charge capacity of the negative electrode by 1.15 times.

[0125] Next, the positive electrode is pressed. A SE layer paste is applied to the surface of the pressed positive electrode layer using an extrusion coating machine. The applied SE layer paste is dried on a heated plate at 100°C for 30 minutes. Then, it is rolled at a linear pressure of 2 tons / cm. This yields a positive electrode-side laminate having a positive current collector, a positive electrode layer, and a solid electrolyte layer. Next, the negative electrode is pressed. A SE layer paste is applied to the surface of the pressed negative electrode layer using an extrusion coating machine. The applied SE layer paste is dried on a heated plate at 100°C for 30 minutes. Then, it is rolled at a linear pressure of 2 tons / cm. This yields a negative electrode-side laminate having a negative current collector, a negative electrode layer, and a solid electrolyte layer.

[0126] The positive and negative electrode stacks were punched separately and then arranged with solid electrolyte layers facing each other, with an unpressed solid electrolyte layer placed between them. Then, they were rolled at 130°C with a linear pressure of 2 tons / cm to obtain a power generation element having a positive electrode, a solid electrolyte layer, and a negative electrode in sequence. The resulting power generation element was laminated and sealed, and constrained at 5 MPa, thus obtaining an all-solid-state battery for evaluation.

[0127] [Calculation of the ratio (A / B) (%)]

[0128] The power generation element of the all-solid-state battery fabricated in the embodiment was exposed. This all-solid-state battery was placed in a chamber not exposed to the atmosphere and transferred to a vacuum electronic staining apparatus (VSC4TWDH (manufactured by Filgen Corporation)). After creating a vacuum atmosphere inside the vacuum electronic staining apparatus, osmium tetroxide (OsO4) gas was introduced, the chamber was opened, and the staining time and gas concentration were adjusted to perform osmium (Os) staining.

[0129] (Production of the experimental film)

[0130] Osmium-stained power generation components were cut to appropriate sizes under an inert atmosphere to prepare test pieces. The cut surfaces of the test pieces were then machined under a vacuum atmosphere using an ion milling apparatus (IM4000PLUS manufactured by Hitachi High Technology Co., Ltd.).

[0131] (Image Acquisition)

[0132] After cross-section processing, the test specimen was introduced into a field emission scanning electron microscope (FE-SEM "Regulus 8230" manufactured by Hitachi High Technology Corporation). During the process from cross-section processing to introduction into the SEM, a vacuum atmosphere was maintained to prevent the test specimen from being exposed to the atmosphere.

[0133] The cross-section of the negative electrode layer of the experimental specimen was observed using FE-SEM. Six observation positions were set at approximately equal intervals along a plane parallel to the negative electrode current collector, i.e., orthogonal to the thickness direction of the negative electrode layer. Furthermore, locations where the conductive material would not be reflected were chosen as observation positions. Secondary electron images and reflected electron images were obtained at each observation position using SEM. The magnification was 5000x. At the same observation positions, elemental mapping images of carbon (C), sulfur (S), and sulfur (S) and osmium (Os) were obtained using EDX. Figure 4A SEM image representing the cross-section of the negative electrode layer. Figure 4B A mapping image representing carbon (C-image), Figure 4C A mapping image representing sulfur (S-image), Figure 4D Mapping images of sulfur and osmium (S, Os images).

[0134] (Image Analysis)

[0135] Using the images obtained above, (1) the total content B of the rubber-based adhesive was determined, and (2) the amount A of the rubber-based adhesive adsorbed on lithium titanate was determined.

[0136] (1) Determination of the total content B of rubber-based adhesives

[0137] First, the carbon mapping image (C image) is binarized. The number of pixels P1 in the extracted C element image is counted, resulting in 193,890 pixels.

[0138] Next, the sulfur-mapping image (S image) is binarized. The number of pixels P2 in the extracted S element image is counted, resulting in 100,660 pixels.

[0139] Next, calculate the number of pixels P3 after subtracting P2 from P1, which is 93230 pixels.

[0140] (2) Determination of the adsorption amount A of rubber-based adhesives adsorbed on lithium titanate

[0141] Figures 5A to 5C This is an image processing diagram of the process used to extract the adhesive adsorbed on the lithium titanate of the negative electrode layer of the evaluation battery obtained in the examples. First, the obtained sulfur (S) and osmium (Os) mapping image is generated by coloring the regions where Os and S elements are present (red) and the other regions (black). Figure 5A Separation Figure 5B Next, by removing large areas (regions consisting of S from the sulfide solid electrolyte and Os covering the S from the sulfide solid electrolyte), the residual Os elements, i.e., the Os elements adsorbed on lithium titanate, are extracted. Figure 5CThe number of pixels P4 extracted from the Os element is counted, and the result is 1265 pixels.

[0142] The ratio of the amount of rubber-based adhesive adsorbed on lithium titanate to the total amount of rubber-based adhesive B contained in the negative electrode layer was calculated by dividing the number of pixels P4 obtained in (2) above by the number of pixels P3 obtained in (1) above and expressing it as a percentage ((P4 / P3)×100(%)), and the result was 1.35%.

[0143] [Comparative Example]

[0144] First, Li4Ti5O, as the negative electrode active material, was weighed in the same manner as in the example. 12 Particles (LTO, density 3.5 g / cc), conductive material (VGCF, density 2 g / cc), binder (SBR, density 0.9 g / cc), dispersion medium (butyl butyrate), and sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5 series glass ceramic, density 2 g / cc).

[0145] according to Figure 3 The flowchart shown illustrates the process for obtaining a negative electrode paste. First, the LTO particles described above are added to the dispersion medium and dispersed using an ultrasonic homogenizer (SMT UH-50) to obtain a precursor dispersion. Next, the binder described above is added to the obtained precursor dispersion and dispersed using an ultrasonic homogenizer (SMT UH-50) to obtain a dispersion. Then, the sulfide solid electrolyte described above is added to the dispersion and dispersed using an ultrasonic homogenizer (SMT UH-50) to obtain a negative electrode paste. Except for using the obtained negative electrode paste, an all-solid-state battery for evaluation is obtained in the same manner as in the examples.

[0146] For the all-solid-state batteries used for evaluation manufactured in the comparative examples, the same methods as in the examples were used for the fabrication of test pieces, image acquisition, and image analysis. Figures 6A to 6F These are SEM images of the negative electrode layer cross-section of the evaluation battery obtained in the examples and comparative examples, elemental mapping images, and extracted images of the adhesive adsorbed on lithium titanate. In the comparative examples, the number of pixels P1 in the extracted image of element C was calculated to be 690,624 pixels, the number of pixels P2 in the extracted image of element S was 241,380 pixels, and the number of pixels P3 was 449,244 pixels. In addition, the number of pixels P4 was 21,008 pixels. Figure 6D SEM image showing the cross-section of the negative electrode layer of the comparative example. Figure 6E Mapping images representing sulfur and osmium (S, Os images), Figure 6FThe image shows the Os image of the extracted LTO adsorbed. From this, the ratio of the adsorption amount A of the rubber-based binder on the lithium titanate to the total content B of the rubber-based binder in the negative electrode layer is calculated to be 4.68%. Furthermore, for comparison, SEM images, S, Os images, and the Os image of LTO adsorbed from the all-solid-state battery used for the evaluation of the example are shown below. Figure 6A , Figure 6B and Figure 6C .

[0147] [evaluate]

[0148] (DC resistance measurement)

[0149] The DC resistance of the all-solid-state batteries fabricated in the examples and comparative examples was determined. Specifically, the all-solid-state batteries were charged at a constant current equivalent to 1C, and after the battery voltage reached 2.95V, constant voltage charging was performed, ending when the charging current reached 0.01C. Then, constant current discharging was performed at a current equivalent to 1C, ending when the constant current discharge reached 1.5V. Then, the all-solid-state batteries were charged at a constant current equivalent to 3C. The DC resistance (charging resistance) was calculated by dividing the difference between the voltage before charging and the voltage after 10 seconds of charging by the current equivalent to 3C. The results are shown in Table 1. Furthermore, the charging resistance ratios in Table 1 are relative values ​​with respect to the comparative examples.

[0150] Table 1

[0151]

[0152] As shown in Table 1, it was confirmed that the charging resistance ratio of the embodiments was lower than that of the comparative examples. It is speculated that the reason why the charging resistance ratio of the embodiments was lower than that of the comparative examples is that the amount of binder adsorbed on the negative electrode active material (lithium titanate) is lower relative to the total amount of binder in the negative electrode layer, thus suppressing the reduction of the reaction area of ​​the negative electrode active material.

Claims

1. A negative electrode layer for a all-solid battery, characterized by, contains: lithium titanate, a sulfide solid electrolyte, and a rubber-based binder, a proportion A / B of an adsorption amount A of the rubber-based binder adsorbed on the lithium titanate with respect to a total content B of the rubber-based binder contained in the negative electrode layer is 1.35% or less.

2. The negative electrode layer according to claim 1, characterized in that the rubber-based binder contains a styrene-butadiene rubber.

3. The negative electrode layer according to claim 1 or 2, characterized in that The lithium titanate has a composition represented by Li4Ti5O 12 .

4. The negative electrode layer according to claim 1 or 2, characterized in that a proportion of the rubber-based binder in the negative electrode layer is 1% by volume or more and 20% by volume or less, a proportion of the lithium titanate in the negative electrode layer is 20% by volume or more and 80% by volume or less, a proportion of the sulfide solid electrolyte in the negative electrode layer is 15% by volume or more and 75% by volume or less.

5. The negative electrode layer according to claim 3, characterized in that a proportion of the rubber-based binder in the negative electrode layer is 1% by volume or more and 20% by volume or less, a proportion of the lithium titanate in the negative electrode layer is 20% by volume or more and 80% by volume or less, a proportion of the sulfide solid electrolyte in the negative electrode layer is 15% by volume or more and 75% by volume or less.

6. A method for manufacturing a negative electrode layer for an all-solid battery, which is a method for manufacturing the negative electrode layer according to any one of claims 1 to 5, characterized by comprises the following steps: preparing a dispersion obtained by dispersing a sulfide solid electrolyte and a first component in a dispersion medium; adding a second component to the dispersion and dispersing it to obtain a negative electrode paste; and applying the negative electrode paste and drying it to form a negative electrode layer, one of the first component and the second component is lithium titanate, and the other is a rubber-based binder.

7. The method for manufacturing a negative electrode layer according to claim 6, characterized in that the first component is the lithium titanate, and the second component is the rubber-based binder.

8. The method for manufacturing a negative electrode layer according to claim 6 or 7, characterized in that the step of preparing the dispersion comprises the following steps: adding the first component to the dispersion medium and performing a first dispersion treatment, thereby obtaining a precursor dispersion; adding the sulfide solid electrolyte to the precursor dispersion and performing a second dispersion treatment, thereby obtaining the dispersion.

9. An all-solid battery having the negative electrode layer according to any one of claims 1 to 5, further comprising: a positive electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer.

Images