JP7631912B2 - Method for manufacturing anode and method for manufacturing all-solid-state battery - Google Patents

Description

This disclosure relates to a method for manufacturing a negative electrode.

All-solid-state batteries are batteries that have a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer, and have the advantage that safety devices can be simplified more easily than liquid batteries that have an electrolyte solution that contains a flammable organic solvent.

Si-based active materials are known as negative electrode active materials with good capacity characteristics. Patent Document 1 discloses a negative electrode for a sulfide all-solid-state battery that contains at least one material selected from the group consisting of Si and Si alloys as the negative electrode active material.

Furthermore, although not a technology related to all-solid-state batteries, Patent Document 2 discloses a negative electrode for a nonaqueous electrolyte secondary battery, which has a current collector, a first layer containing lithium titanate, and a second layer containing a carbon material, in which the ratio _T1 / _T2 of the thickness _T2 of the first layer to the thickness T1 of the second layer is 0.15 or more _and 0.55 or less.

Patent Document 3 discloses an all-solid-state battery that contains a sulfide solid electrolyte and a halide solid electrolyte as the solid electrolyte. Patent Document 4 discloses a method for manufacturing a battery electrode that includes a coating process in which an electrode active material slurry containing an electrode active material and an electrolyte is applied to the surface of a current collector to form a coating film.

JP 2018-142431 A JP 2014-199714 A International Publication No. 2019-135323 JP 2020-087863 A

For example, in order to reduce the amount of heat generated during a short circuit, it is effective to provide a coating layer, which will be described later, between the negative electrode current collector and the negative electrode active material layer. On the other hand, for example, if the end of the negative electrode active material layer is electrically connected to the negative electrode current collector without the coating layer, that part becomes an electronic conduction path, and the function of the coating layer to reduce the amount of heat generated is reduced.

The present disclosure has been made in consideration of the above-mentioned circumstances, and has as its main objective the provision of a method for producing a negative electrode that can obtain a negative electrode in which the deterioration of the heat generation reducing function of the coating layer is suppressed.

In order to solve the above problems, the present disclosure provides a method for producing a negative electrode used in an all-solid-state battery, the method comprising: a coating layer forming step of coating a first slurry containing an oxide active material as a first active material onto a negative electrode current collector to form a coating layer; and a negative electrode active material layer forming step of coating a second slurry containing a second active material onto the coating layer to form a negative electrode active material layer, wherein in the coating layer forming step and the negative electrode active material layer forming step, the coating layer and the negative electrode active material layer are formed so as to satisfy: ( _{i) when an end angle of the coating layer in the coating width direction is θ1 and an} end angle of the negative electrode active material layer is θ2, _θ2 / _θ1 >₁; and (ii) when a coating sagging width of the coating layer in the coating width direction is W1 and a coating sagging width of the negative electrode active material layer is W2, _W2 / _W1 ≦0.97.

According to the present disclosure, by forming the coating layer and the negative electrode active material layer so as to satisfy (i) and (ii), a negative electrode can be obtained in which the deterioration of the heat generation reducing function of the coating layer is suppressed.

In the above disclosure, the _W2 / _W1 may be 0.85≦ _W2 / _W1 .

In the above disclosure, the method for manufacturing the negative electrode may include a pressing step in which the coating layer and the negative electrode active material layer are pressed in the thickness direction.

In the above disclosure, the method for manufacturing the negative electrode may include a negative electrode tab forming step of forming a negative electrode tab including an end of the coating layer and an end of the negative electrode active material layer.

In the above disclosure, the first active material may be at least one of lithium titanate and niobium titanium oxide.

In the above disclosure, the coating layer may contain at least one of a conductive material, a solid electrolyte, and a binder.

In the above disclosure, the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer may be 3% or more and 13% or less.

In the above disclosure, the second active material may have an overall expansion rate upon charging of 14% or more.

In the above disclosure, the second active material may be a Si-based active material.

The present disclosure also provides a method for producing an all-solid-state battery, which includes a negative electrode production process for producing a negative electrode by the above-mentioned negative electrode production method.

According to the present disclosure, by producing a negative electrode using the above-mentioned manufacturing method, an all-solid-state battery having a negative electrode in which the deterioration of the heat generation reducing function of the coating layer is suppressed can be obtained.

The present disclosure has the effect of providing a negative electrode that suppresses the deterioration of the heat generation reducing function of the coating layer.

1A to 1C are schematic cross-sectional views illustrating a method for producing a negative electrode in the present disclosure. FIG. 2 is a schematic cross-sectional view illustrating a negative electrode according to the present disclosure. FIG. 2 is a schematic plan view illustrating a negative electrode tab forming step in the present disclosure. FIG. 1 is a schematic cross-sectional view illustrating an all-solid-state battery according to the present disclosure. FIG. 2 is a schematic plan view illustrating a negative electrode prepared in an example. FIG. 2 is a schematic plan view illustrating an evaluation sample prepared in the examples. 1 shows the results of resistance measurement for evaluation samples prepared in Examples 1 to 4 and Comparative Examples 1 to 7. 1 shows the results of resistance measurement for evaluation samples prepared in Examples 1 to 4 and Comparative Examples 1 to 7.

The manufacturing method of the negative electrode and the manufacturing method of the all-solid-state battery in the present disclosure will be described in detail below with reference to the drawings. Each of the figures shown below is a schematic illustration, and the size and shape of each part are appropriately exaggerated to facilitate understanding. In addition, hatching showing the cross section of a member is appropriately omitted in each of the figures. In addition, in this specification, when expressing an aspect in which another member is arranged relative to a certain member, the term "above" or "below" simply refers to both a case in which another member is arranged directly above or below a certain member so as to be in contact with the certain member, and a case in which another member is arranged above or below a certain member via another member, unless otherwise specified.

A. Method for manufacturing a negative electrode Fig. 1 is a schematic cross-sectional view illustrating a method for manufacturing a negative electrode in the present disclosure. In Fig. 1, first, a negative electrode current collector 1 is prepared (Fig. 1(a)). Next, a first slurry containing an oxide active material as a first active material is applied onto the negative electrode current collector 1 to form a coating layer 2 (Fig. 1(b)). Next, a second slurry containing a second active material is applied onto the coating layer 2 to form a negative electrode active material layer 3 (Fig. 1(c)). This results in a negative electrode AN.

In the present disclosure, the coating layer and the negative electrode active material layer are formed so as to satisfy a predetermined condition. Here, as shown in FIG. 2(a), in the coating width direction _DW , the coating sagging width of the coating layer is _W1 , and the coating sagging width of the negative electrode active material layer 3 is _W2 . The coating sagging width refers to the surplus width (per one end) with respect to the coating width W. For example, in FIG. 2(a), when the total width of the coating layer 2 in the coating width direction _DW is _WT , the relationship _WT = W + _2W1 usually holds. In other words, the coating sagging width ( _W1 , _W2 ) refers to the width of the region that flows outward from the coating end α. Also, as shown in FIG. 2(b), in the coating width direction _DW , the end angle of the coating layer 2 is _θ1 , and the end angle of the negative electrode active material layer 3 is _θ2 . The end angle refers to the rising angle from the bottom surface at the end. In the present disclosure, the coating layer and the negative electrode active material layer are formed so as to satisfy (i) θ ₂ /θ ₁ >1 and (ii) W ₂ /W ₁ ≦0.97. In the examples described later, W ₂ /W ₁ is approximately 1, and the dimensions are deformed in FIGS. 2(a) and (b) for ease of understanding. As shown in FIG. 2(a), the end 3t of the negative electrode active material layer 3 is preferably located inside the end 2t of the coating layer 2. Furthermore, the end 3t of the negative electrode active material layer 3 is preferably located inside the abrupt decrease portion (a portion where the thickness decreases in the outward direction due to surface tension) including the end 2t of the coating layer 2. In addition, in the coating layer 2 shown in FIG. 2(a), the region flowing outward from the coating end α has abrupt decrease portion and gradual decrease portion (a portion where the rate of decrease in thickness in the outward direction is smaller than that of the abrupt decrease portion), but the region flowing outward from the coating end α may have only abrupt decrease portion and may not have a gradual decrease portion.

According to the present disclosure, by forming the coating layer and the negative electrode active material layer so as to satisfy (i) and (ii), a negative electrode in which the deterioration of the heat generation reducing function of the coating layer is suppressed can be obtained. Here, as described above, in order to reduce the amount of heat generated, for example, during a short circuit, it is effective to provide a coating layer containing an oxide active material between the negative electrode current collector and the negative electrode active material layer. When Li is inserted into the oxide active material, electronic conductivity is exhibited, and when the inserted Li is removed, insulating properties are exhibited. Therefore, an increase in internal resistance can be suppressed by forming an electronic conduction path using the electronic conductivity of the oxide active material. On the other hand, for example, when a short circuit occurs, Li is removed from the oxide active material, and the amount of heat generated can be reduced by blocking the electronic conduction path using its insulation (shutdown function).

In this way, by providing a coating layer containing an oxide active material between the negative electrode current collector and the negative electrode active material layer, it is possible to reduce the amount of heat generated, for example, during a short circuit. On the other hand, for example, if the end of the negative electrode active material layer is electrically connected to the negative electrode current collector without the coating layer, this portion becomes an electronic conduction path, and the heat generation reduction function of the coating layer is reduced. In the present disclosure, by forming the coating layer and the negative electrode active material layer so as to satisfy (i) and (ii), it is possible to prevent the end of the negative electrode active material layer from being electrically connected to the negative electrode current collector without the coating layer, and to obtain a negative electrode in which the reduction in the heat generation function of the coating layer is suppressed.

1. Coating Layer Forming Step The coating layer forming step in the present disclosure is a step of applying a first slurry containing an oxide active material as a first active material onto a negative electrode current collector to form a coating layer.

The method for applying the first slurry is not particularly limited, but is preferably, for example, a method that can apply the slurry in a predetermined width. In that case, a striped coating layer is obtained. A specific example of a method for applying the first slurry is a doctor blade method using an applicator. After application of the first slurry, drying may be performed to remove the dispersion medium.

The first slurry contains an oxide active material which is a first active material. The oxide active material usually has electronic conductivity when Li is inserted, and has insulating properties when the inserted Li is removed. The electronic conductivity (25°C) of the oxide active material when Li is inserted is, for example, 8.0 x ^10-1 S/cm or more. On the other hand, the electronic conductivity (25°C) of the oxide active material when the inserted Li is removed is, for example, 2.1 x ^10-6 S/cm or less.

The oxide active material contains at least a metal element and an oxygen element. In addition, the oxide active material preferably has at least one of a layered structure and a spinel structure. An example of the oxide active material is lithium titanate. The lithium titanate is a compound containing Li, Ti, and O, and examples thereof include Li ₄ Ti ₅ O ₁₂ , Li ₄ TiO ₄ , Li ₂ TiO ₃ , and Li ₂ Ti ₃ O _7. Another example of the oxide active material is niobium titanium oxide. The niobium titanium oxide is a compound containing Ti, Nb, and O, and examples thereof include TiNb ₂ O ₇ and Ti ₂ Nb ₁₀ O _29. The first slurry may contain only one type of oxide active material, or may contain two or more types. In addition, the oxide active material preferably has a higher Li insertion/extraction potential than the second active material.

The shape of the oxide active material may be, for example, particulate. The average particle size (D ₅₀ ) of the oxide active material is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size (D ₅₀ ) of the oxide active material may be, for example, 50 μm or less, or 20 μm or less. The average particle size (D ₅₀ ) can be calculated, for example, from measurements using a laser diffraction particle size distribution meter or a scanning electron microscope (SEM). The ratio of the oxide active material in the solid content of the first slurry is, for example, 50% by weight or more, may be 70% by weight or more, or may be 90% by weight or more.

The first slurry usually contains a dispersion medium. The type of dispersion medium is not particularly limited, but examples include ketones such as diisobutyl ketone, alkanes such as heptane, and esters such as butyl butyrate.

The first slurry may or may not contain a conductive material. By adding a small amount of conductive material, the shutdown function works quickly and the amount of heat generated can be further reduced. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF).

The proportion of the conductive material in the solid content of the first slurry is, for example, 1% by weight or less, may be 0.5% by weight or less, or may be 0.3% by weight or less. The proportion of the conductive material may be 0% by weight or more than 0% by weight, and in the latter case, is, for example, 0.05% by weight or more.

The first slurry may or may not contain a solid electrolyte. By adding a solid electrolyte, a good ion conduction path is formed in the coating layer, the shutdown function works quickly, and the amount of heat generated can be further reduced. On the other hand, by not adding a solid electrolyte, an increase in internal resistance can be suppressed. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

Examples of the sulfide solid electrolyte include solid electrolytes containing Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and halogen. Examples of halogen elements include F, Cl, Br, and I. The sulfide solid electrolyte may be glass (amorphous), glass ceramic, or crystal. Examples of sulfide solid electrolytes include Li ₂ S-P ₂ S ₅ , LiI-Li ₂ S-P ₂ S ₅ , LiI-LiBr-Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , and Li ₂ S-P ₂ S ₅ -GeS ₂ .

The proportion of the solid electrolyte in the solid content of the first slurry is, for example, 5 vol.% or more, and may be 10 vol.% or more. On the other hand, the proportion of the solid electrolyte in the solid content of the first slurry is, for example, 30 vol.% or less.

The first slurry preferably contains a binder. Adding a binder improves the adhesiveness of the coating layer and improves the adhesion between the negative electrode active material layer and the negative electrode current collector. Examples of binders include fluoride-based binders, polyimide-based binders, and rubber-based binders. The content of the binder in the solid content of the first slurry is, for example, 1% by weight or more and 10% by weight or less.

The negative electrode current collector is a member that collects the current from the negative electrode active material layer. Examples of the negative electrode current collector include metal current collectors. Examples of the metal current collector include current collectors having metals such as Cu and Ni. The metal current collector may be a simple substance of the above metal, or an alloy of the above metal. Examples of the shape of the negative electrode current collector include a foil shape. The surface roughness (Rz) of the negative electrode current collector is, for example, 2 μm or more, or may be 4 μm or more, or may be 6 μm or more. On the other hand, the surface roughness (Rz) of the negative electrode current collector is, for example, 9 μm or less.

2. Negative electrode active material layer forming step In the present disclosure, a negative electrode active material layer forming step is a step of applying a second slurry containing a second active material onto the coating layer to form a negative electrode active material layer. The negative electrode active material layer is preferably formed so as not to protrude from the coating layer in a plan view.

The method for applying the second slurry is not particularly limited, but is preferably a method that can apply the slurry in a predetermined width. In that case, a striped negative electrode active material layer is obtained. A specific example of a method for applying the second slurry is a doctor blade method using an applicator. After application of the second slurry, drying may be performed to remove the dispersion medium.

The coating width of the second slurry is W _S and the coating width of the first slurry is W _{F. W S} /W _F may be, for example, 1 or less than 1. On the other hand, W _S /W _F may be, for example, 0.8 or more, and may be 0.9 or more. The coating width of the slurry can be appropriately adjusted according to the shape of the target all-solid-state battery. The difference between the coating end when forming the negative electrode active material layer and the coating end when forming the coat layer is not particularly limited, but may be, for example, 1 cm or less, and may be 0.5 cm or less.

In the present disclosure, the coating layer and the negative electrode active material layer are formed so as to satisfy the following (i) and (ii).
(i) When the end angle of the coating layer in the coating width direction is _θ1 and the end angle of the negative electrode active material layer is _θ2 , _θ2 / _θ1 >1. (ii) When the coating sagging width of the coating layer in the coating width direction is _W1 and the coating sagging width of the negative electrode active material layer is _W2 , _W2 / _W1 ≦0.97.

In (i), _θ2 / _θ1 is usually greater than 1, and may be 1.1 or more, or may be 1.5 or more. Meanwhile, _θ2 / _θ1 is, for example, 10 or less, or may be 5 or less. Each of _θ1 and _θ2 is, for example, 10° or more, or may be 20° or more, or may be 30° or more. Meanwhile, each of _θ1 and _θ2 is, for example, 70° or less, or may be 65° or less.

In (ii), _W2 / _W1 is usually 0.97 or less, may be 0.96 or less, or may be 0.95 or less. If _W2 / _W1 is too large, the heat generation reducing function of the coating layer may not be sufficiently suppressed. _W2 / _W1 is, for example, 0.80 or more, and may be 0.85 or more. If _W2 / _W1 is too small, the volumetric energy density of the all-solid-state battery may be small.

The coating layer and the negative electrode active material layer have two ends in the coating width direction, and one of the ends may satisfy (i) and (ii), or both ends may satisfy (i) and (ii), with the latter being preferred.

The second slurry contains at least a second active material. The second active material is not particularly limited and may be a general negative electrode active material, but it is preferable that the second active material has an overall expansion rate due to charging of 14% or more. This is because active materials with a large overall expansion rate due to charging tend to have high capacity characteristics. In addition, when the capacity characteristics are high, the amount of heat generated during a short circuit, for example, tends to be large. However, in the present disclosure, by providing the above-mentioned coating layer, it is possible to suppress the increase in the amount of heat generated while maintaining high capacity characteristics.

Here, graphite, which is known as a common negative electrode active material, has a total expansion rate upon charging of 13.2% (Simon Schweidler et al., “Volume Changes of Graphite Anodes Revisited: A Combined Operando X-ray Diffraction and In Situ Pressure Analysis Study”, J. Phys. Chem. C 2018, 122, 16, 8829-8835). In other words, a second active material having a total expansion rate upon charging of 14% or more is an active material having a total volume expansion rate upon charging greater than that of graphite. The total volume expansion rate upon charging can be determined by space-group-independent evaluation as described in Simon Schweidler et al. The second active material may have a total expansion rate upon charging of 100% or more, or 200% or more.

An example of the second active material is a Si-based active material. The Si-based active material is an active material containing Si element. Examples of the Si-based active material include simple Si, Si alloys, and Si oxides. It is preferable that the Si alloy contains the Si element as the main component. Another example of the second active material is a Sn-based active material. The Sn-based active material is an active material containing the Sn element. Examples of the Sn-based active material include simple Sn, Sn alloys, and Sn oxides. It is preferable that the Sn alloy contains the Sn element as the main component.

The shape of the second active material may be, for example, particulate. The average particle size ( _D50 ) of the second active material is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more. On the other hand, the average particle size ( _D50 ) of the second active material is, for example, 50 μm or less, or may be 20 μm or less.

The proportion of the second active material in the solid content of the second slurry is, for example, 20% by weight or more, and may be 40% by weight or more. It may also be 60% by weight or more. On the other hand, the above proportion of the second active material is, for example, 80% by weight or less. In addition, the second slurry usually contains a dispersion medium, and may contain at least one of a conductive material, a solid electrolyte, and a binder. These materials are the same as those in the first slurry described above.

In the present disclosure, the thickness of the coating layer is _T1 , and the thickness of the negative electrode active material layer is _T2 . The ratio of _{T1 to T2 ( T1} / _T2 ) is, for example, 3% or more, and may be 5% or more. If _T1 / _T2 is too small, it is difficult to obtain the effect of reducing the amount of heat generated. On the other hand, the ratio of _T1 to _T2 ( _T1 / _T2 ) is, for example, 20% or less, and may be 13% or less, or 10% or less. If _T1 / _T2 is too large, the internal resistance is likely to increase.

_T1 may be, for example, 2 μm or more, 3 μm or more, or 4 μm or more. Meanwhile, _T1 may be, for example, 15 μm or less, or 10 μm or less. Meanwhile, _T2 may be, for example, 20 μm or more, or 40 μm or more. Meanwhile, _T2 may be, for example, 200 μm or less, or 150 μm or less.

3. Pressing process The method for producing a negative electrode in the present disclosure may include a pressing process for pressing the coating layer and the negative electrode active material layer along the thickness direction. Pressing improves the density of the layers. Even if the end of the negative electrode active material layer is stretched outward by pressing, the coating layer and the negative electrode active material layer are formed so as to satisfy the above-mentioned (i) and (ii), thereby suppressing the deterioration of the heat generation reducing function of the coating layer.

Examples of the pressing method in the pressing process include plate pressing and roll pressing. The pressing pressure is, for example, 200 MPa or more, may be 400 MPa or more, or may be 600 MPa or more. The pressing pressure is, for example, 1000 MPa or less.

The method for producing a negative electrode according to the present disclosure may include a negative electrode tab forming step of forming a negative electrode tab including an end of the coating layer and an end of the negative electrode active material layer. By forming the coating layer and the negative electrode active material layer so as to satisfy the above-mentioned (i) and (ii), it is possible to prevent the end of the negative electrode active material layer from being electrically connected to the negative electrode current collector in the negative electrode tab without passing through the coating layer.

Figure 3 is a schematic plan view illustrating the negative electrode tab forming process in the present disclosure. As shown in Figure 3(a), by cutting so as to leave the end 2t of the coating layer 2 and the end 3t of the negative electrode active material layer 3, as shown in Figure 3(b), a negative electrode tab 1T having the end 2t of the coating layer 2 and the end 3t of the negative electrode active material layer 3 is obtained. Examples of cutting methods include laser cutting, die pressing, and slitting.

B. Manufacturing Method of All-Solid-State Battery The manufacturing method of an all-solid-state battery in the present disclosure includes a negative electrode manufacturing step of manufacturing a negative electrode by the above-described negative electrode manufacturing method.

According to the present disclosure, by producing a negative electrode using the above-mentioned manufacturing method, it is possible to obtain an all-solid-state battery having a negative electrode in which the deterioration of the heat generation reducing function of the coating layer is suppressed.

1. Negative Electrode Manufacturing Process The negative electrode manufacturing process in the present disclosure is similar to that described above in "A. Negative Electrode Manufacturing Method," and therefore will not be described here.

2. Positive electrode preparation step The manufacturing method of the all-solid-state battery in the present disclosure may include a positive electrode preparation step of preparing a positive electrode having a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode may be prepared by oneself or purchased from another party. The method of preparing the positive electrode is not particularly limited, but for example, a method of applying a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector to form a positive electrode active material layer may be mentioned.

Examples of materials for the positive electrode current collector include metals and carbon. The positive electrode slurry contains at least a positive electrode active material and a dispersion medium, and may further contain at least one of a conductive material, a solid electrolyte, and a binder. Examples of the positive electrode active material include oxide active materials. The conductive material, solid electrolyte, and binder are the same as those described above in "A. Method for manufacturing a negative electrode." The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

3. Solid electrolyte layer preparation step The manufacturing method of the all-solid-state battery in the present disclosure may have a solid electrolyte layer preparation step of preparing a solid electrolyte layer. The solid electrolyte layer may be prepared by oneself or purchased from another party. The method of preparing the solid electrolyte layer is not particularly limited, but may be, for example, a method of coating a slurry for the solid electrolyte layer containing a solid electrolyte on a metal foil. The slurry for the solid electrolyte layer contains at least a solid electrolyte and a dispersion medium, and may further contain a binder. The solid electrolyte and the binder are the same as those described in "A. Method for manufacturing a negative electrode" above. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

The method for producing an all-solid-state battery according to the present disclosure may include a lamination step of laminating a positive electrode, a solid electrolyte layer, and a negative electrode in the thickness direction in this order. Specifically, the layers are laminated such that the solid electrolyte layer is disposed between the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode.

5. All-solid-state battery Fig. 4 is a schematic cross-sectional view illustrating an all-solid-state battery in the present disclosure. The all-solid-state battery 10 shown in Fig. 4 has a positive electrode CA having a positive electrode active material layer 5 and a positive electrode current collector 4, a negative electrode AN having a negative electrode active material layer 3, a coating layer 2 and a negative electrode current collector 1, and a solid electrolyte layer 6 disposed between the positive electrode active material layer 5 and the negative electrode active material layer 3.

The all-solid-state battery in this disclosure is typically an all-solid-state lithium-ion secondary battery. Applications of the all-solid-state battery are not particularly limited, but examples include power sources for vehicles such as hybrid automobiles, electric automobiles, gasoline automobiles, and diesel automobiles. In particular, it is preferable to use the all-solid-state battery as a driving power source for hybrid automobiles or electric automobiles. The all-solid-state battery in this disclosure may also be used as a power source for moving objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as a power source for electrical products such as information processing devices.

This disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and anything that has substantially the same configuration as the technical ideas described in the claims of this disclosure and has similar effects is included within the technical scope of this disclosure.

[Example 1]
(Preparation of negative electrode current collector having coating layer)
LTO particles (Li ₄ Ti ₅ O ₁₂ , average particle size 0.7 μm) and a binder (SBR) were prepared. These were weighed so that the weight ratio of LTO particles:binder was 95:5, and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a coating layer slurry. The obtained coating layer slurry was applied onto a negative electrode current collector (Ni foil) by a blade coating method using an applicator, and dried under conditions of 100° C. for 30 minutes. The coating width of the applicator was 90 mm. As a result, a negative electrode current collector 1 having a coating layer 2 (thickness 5 μm) was obtained, as shown in FIG. 5 (a).

(Preparation of negative electrode)
Si particles (average particle size 2 μm), sulfide solid electrolyte (10LiI-15LiBr-75 (0.75Li ₂ S-0.25P ₂ S ₅ ), average particle size 0.5 μm), conductive material (VGCF) and binder (SBR) were prepared. These were weighed out so that the weight ratio of Si particles: sulfide solid electrolyte: conductive material: binder was 47.0: 44.6: 7.0: 1.4, and mixed with a dispersion medium (diisobutyl ketone). The obtained mixture was dispersed with an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a negative electrode slurry. The obtained negative electrode slurry was applied onto the above-mentioned coating layer and dried under conditions of 100 ° C. for 30 minutes. The coating width of the applicator was 90 mm. As a result, a negative electrode having a negative electrode active material layer 3 (thickness 50 μm), a coating layer 2, and a negative electrode current collector 1 was obtained, as shown in FIG. 5(b). The end angle θ ₁ of the coating layer and the end angle θ ₂ of the negative electrode active material layer, as well as the coating sagging width W ₁ of the coating layer and the coating sagging width W ₂ of the negative electrode active material layer, of the obtained negative electrode were measured using a laser microscope. The results are shown in Table 1.

(Preparation of evaluation samples)
The obtained negative electrode was cut to a coating length L of 90 mm, as shown in Fig. 5(b) . Thereafter, as shown in Fig. 6 , the two cut negative electrodes were arranged so that the negative electrode active material layers 3 faced each other, and pressed at 4 tons to obtain an evaluation sample.

[Examples 2 to 4, Comparative Examples 1 to 7]
A negative electrode and an evaluation sample were obtained in the same manner as in Example 1, except that the solid content of the slurry was adjusted so that the end angles θ ₁ and θ ₂ and coating drip widths W ₁ and W ₂ shown in Table 1 were obtained.

[evaluation]
The insulating properties of the evaluation samples prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were evaluated. Specifically, the resistance was measured using a circuit tester. Since the coating layer containing LTO that has not been charged is insulating, the insulating properties of the evaluation sample can be evaluated by measuring the resistance of the evaluation sample. The evaluation results are shown in Table 1, and in Figs. 7 and 8.

As shown in Table 1 and FIG. 7, in Examples 1 to 4 and Comparative Examples 5 to 7, θ ₂ /θ ₁ >1 was satisfied, and in that case, a resistance of the order of MΩ was obtained. That is, it was confirmed that insulation was maintained between the two negative electrode current collectors. This is because the coating layer is insulating in an uncharged state. On the other hand, in Comparative Examples 1 to 4, the negative electrode active material layer protruded from the coating layer, so insulation was not maintained. Note that although the area of the protruding portion was small, it is presumed that if, for example, a metal foreign object gets into the end of the protruding portion, the heat generation reduction function of the coating layer will be significantly reduced.

8, it was confirmed that in Examples 1 to 4, _W2 / _W1 ≦0.97 was satisfied, and the resistance was significantly higher than that in Comparative Examples 5 to 7. On the other hand, it is presumed that in Comparative Examples 5 to 7, the negative electrode active material layer protruded slightly from the coating layer during pressing, and the heat generation reducing function of the coating layer was slightly reduced. In this way, it was confirmed that the use of a negative electrode that satisfied _θ2 / _θ1 >1 and _W2 / _W1 ≦0.97 could suppress the reduction in the heat generation reducing function of the coating layer.

Reference Signs List 1: negative electrode current collector 2: coating layer 3: negative electrode active material layer 4: positive electrode current collector 5: positive electrode active material layer 6: solid electrolyte layer 10: all-solid-state battery

Claims (9)

A method for producing a negative electrode for use in an all-solid-state battery, comprising the steps of:
a coating layer forming step of applying a first slurry containing an oxide active material as a first active material onto a negative electrode current collector by a doctor blade method using an applicator to form a coating layer;
a negative electrode active material layer forming step of applying a second slurry containing a second active material onto the coating layer by a doctor blade method using an applicator to form a negative electrode active material layer;
having
In the coating layer forming step and the negative electrode active material layer forming step,
(i) when the end angle of the coating layer in the coating width direction is θ ₁ and the end angle of the negative electrode active material layer is θ ₂ , θ ₂ /θ ₁ >1; and
(ii) when the coating sagging width of the coating layer in the coating width direction is _W1 and the coating sagging width of the negative electrode active material layer is _W2 , _W2 / _W1 ≦0.97;
The coating layer and the negative electrode active material layer are formed so as to satisfy
When the coating width of the second slurry is W _S and the coating width of the first slurry is W _F , W _S /W _F is 1;
the first active material is at least one of lithium titanate and niobium titanium oxide;
The method for producing a negative electrode, wherein the coating layer does not contain a conductive material . The method for producing a negative electrode according to claim 1 , wherein the W ₂ /W ₁ ratio satisfies 0.85≦W ₂ /W ₁ . The method for producing the negative electrode according to claim 1 or 2, further comprising a pressing step in which the coating layer and the negative electrode active material layer are pressed in the thickness direction. The method for manufacturing the negative electrode according to any one of claims 1 to 3, comprising a negative electrode tab forming step for forming a negative electrode tab including an end of the coating layer and an end of the negative electrode active material layer. The method for producing a negative electrode according to claim 1 , wherein the coating layer contains at least one of a solid electrolyte and a binder. The method for producing a negative electrode according to claim 1 , wherein a ratio of a thickness of the coating layer to a thickness of the negative electrode active material layer is 3% or more and 13 % or less. The method for producing a negative electrode according to claim 1 , wherein the second active material has an overall expansion rate upon charging of 14% or more. The method for producing a negative electrode according to claim 1 , wherein the second active material is a Si-based active material. A method for producing an all-solid-state battery, comprising: a negative electrode production step of producing a negative electrode by the method for producing a negative electrode according to any one of claims 1 to 8 .