JP6973310B2 - All solid state battery - Google Patents

Description

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

The all-solid-state battery is a battery having a solid electrolyte layer between the positive electrode layer and the negative electrode layer, and has an advantage that the safety device can be easily simplified as compared with a liquid-based battery having an electrolytic solution containing a flammable organic solvent. Have.

For example, in Patent Document 1, the mixing ratio of the active material constituting the polar material layer in at least one of the positive electrode material layer and the negative electrode material layer with respect to the solid electrolyte is continuously or stepwise according to the distance from the current collector. All-solid-state lithium-ion secondary batteries have been reduced to. Further, Patent Document 2 describes a solid electrolyte battery having an intermediate layer between the electrode layer and the solid electrolyte layer, in which the content of the active material is gradually reduced from the electrode side of the intermediate layer to the solid electrolyte side. Batteries are disclosed.

On the other hand, although it is not a technique relating to an all-solid-state battery, Patent Document 3 discloses a battery in which the mass or electrode density of the active material is the central portion> the end portion in the stacking direction. Similarly, although not a technique relating to an all-solid-state battery, Patent Document 4 discloses a non-aqueous electrolyte secondary battery in which the void ratio in the electrode is increased from the separator toward the current collector.

Japanese Unexamined Patent Publication No. 2011-12028 Japanese Unexamined Patent Publication No. 2000-164252 Japanese Unexamined Patent Publication No. 2013-18775 Japanese Unexamined Patent Publication No. 2014-207201

There is a demand for an all-solid-state battery having good capacity characteristics at a high rate. The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an all-solid-state battery having good capacity characteristics at a high rate.

In order to solve the above problems, in the present disclosure, an all-solid-state battery having a first current collector, a first electrode layer, a solid electrolyte layer, a second electrode layer, and a second current collector in this order. The first electrode layer has a laminated structure in which a plurality of mixture layers containing an active material and a solid electrolyte are laminated, and the volume ratio of the active material to the solid electrolyte in the mixture layer is defined as X. In this case, the volume ratio X decreases from the first current collector toward the solid electrolyte layer in the plurality of mixture layers, and the degree of inclination of the volume ratio defined by the following formula is ΔX. , The above ΔX provides an all-solid-state battery satisfying 0.3 ≦ ΔX ≦ 0.5.
Inclination ΔX = (X _max −X _min ) / X _ave
(In the formula, X _max is the volume ratio in the mixture layer closest to the first current collector, and X _min is the volume ratio in the mixture layer closest to the solid electrolyte layer, and X _ave. Is the average of the volume ratios in the plurality of composite layers)

According to the present disclosure, the volume ratio of the active material in the plurality of mixture layers is lowered from the first electrode layer toward the solid electrolyte layer, and the slope of the volume ratio is set within a predetermined range to increase the volume ratio. An all-solid-state battery having good capacity characteristics at a rate can be obtained.

The all-solid-state battery in the present disclosure has the effect of having good capacity characteristics at high rates.

It is a schematic sectional drawing which shows an example of the all-solid-state battery in this disclosure. It is a graph which shows the charge capacity of the evaluation cell obtained in Examples 1 to 4 and Comparative Examples 1 to 4.

Hereinafter, the all-solid-state battery in the present disclosure will be described in detail.

FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery in the present disclosure. The all-solid-state battery 10 shown in FIG. 1 has a first current collector 1, a first electrode layer 2, a solid electrolyte layer 3, a second electrode layer 4, and a second current collector 5 along the thickness direction. Have in order. Further, the first electrode layer 2 has a laminated structure in which a plurality of mixture layers 2a, 2b, and 2c containing an active material and a solid electrolyte are laminated along the thickness direction. Further, when the volume ratio of the active material to the solid electrolyte in each mixture layer is X, the volume ratio X is the solid electrolyte from the first current collector 1 in the plurality of mixture layers 2a, 2b, and 2c. It is decreasing toward layer 3. That is, the volume ratio X decreases in the order of the mixture layers 2a, 2b, and 2c. Further, as will be described later, one feature of the present disclosure is that ΔX is within a predetermined range when the inclination of the volume ratio is ΔX.

According to the present disclosure, the volume ratio of the active material in the plurality of mixture layers is lowered from the first electrode layer toward the solid electrolyte layer, and the slope of the volume ratio of the active material is set within a predetermined range. Therefore, it is possible to obtain an all-solid-state battery having good capacity characteristics at a high rate.

In an all-solid-state battery, it is necessary to improve the ionic conductivity of the electrode layer in order to realize rapid charging or rapid discharging. In order to improve the ionic conductivity of the electrode layer, it is effective to increase the ratio of the solid electrolyte to the active material. This is because the solid electrolyte has, for example, 1000 times or more the ionic conductivity of the active material. On the other hand, if the proportion of the solid electrolyte is increased, the proportion of the active material is relatively decreased, which is a trade-off that the energy density of the all-solid-state battery is lowered. Therefore, it is difficult to achieve both charge / discharge characteristics at a high rate and good capacitance characteristics.

On the other hand, the first electrode layer in the present disclosure has a plurality of mixture layers. Further, the volume ratio of the active material in the plurality of mixture layers decreases from the first electrode layer toward the solid electrolyte layer. That is, the first electrode layer has a gradation structure in which the volume ratio of the active material in the mixture layer close to the solid electrolyte layer is low and the volume ratio of the active material in the mixture layer close to the first current collector is high. For example, when the first electrode layer is a positive electrode layer, ions are conducted from the positive electrode layer to the solid electrolyte layer during charging, but the volume ratio of the active material is low in the mixture layer close to the solid electrolyte layer (solid electrolyte). The volume ratio is high), and a good ion conduction path is formed. In this way, by adopting the gradation structure, it is possible to improve the charge / discharge characteristics at a high rate.

Further, in the present disclosure, by setting the slope of the volume ratio of the active material within a predetermined range, it is possible to achieve both charge / discharge characteristics at a high rate and good capacity characteristics. As described above, by adopting the gradation structure, the charge / discharge characteristics at a high rate can be improved. On the other hand, the proportion of the active material is relatively small as compared with the case where the gradation structure is not adopted. In order to solve this, it is assumed that the volume ratio of the active material in the mixture layer close to the solid electrolyte layer is sufficiently high, but in that case, unexpectedly, sufficient capacity characteristics cannot be obtained. was there.

On the other hand, in the present disclosure, by setting the slope of the volume ratio of the active material on the solid electrolyte layer side and the first current collector side within a predetermined range, as described in Examples described later, it is specific. It was found that the capacitance characteristics can be improved. That is, in the present disclosure, the volume ratio of the active material in the plurality of mixture layers is lowered from the first electrode layer toward the solid electrolyte layer, and the slope of the volume ratio of the active material is set within a predetermined range. As a result, it was possible to achieve both charge / discharge characteristics at a high rate and good capacitance characteristics.

1. 1. First Electrode Layer The first electrode layer in the present disclosure has a laminated structure in which a plurality of mixture layers containing an active material and a solid electrolyte are laminated. The number of the mixture layers in the first electrode layer is, for example, 2 or more, and may be 3 or more, or 4 or more. On the other hand, the number of the mixture layers in the first electrode layer is, for example, 10 or less, and may be 6 or less.

Further, when the volume ratio of the active material to the solid electrolyte in each mixture layer is X, the volume ratio X decreases from the first current collector toward the solid electrolyte layer in the plurality of mixture layers. doing. That is, the volume ratio X in the mixture layer closest to the first current collector (for example, the mixture layer 2a in FIG. 1) is the highest, and the mixture layer closest to the solid electrolyte layer (for example, the mixture layer 2c in FIG. 1). The volume ratio X in is the lowest.

Further, the slope of the volume ratio defined by the following formula is defined as ΔX.
Inclination ΔX = (X _max −X _min ) / X _ave
In the formula, X _max is the volume ratio in the mixture layer closest to the first current collector (for example, the mixture layer 2a in FIG. 1), and X _min is the volume ratio in the mixture layer closest to the solid electrolyte layer (for example, in FIG. 1). It is the volume ratio in the mixture layer 2c), and X _ave is the average of the volume ratios in the plurality of mixture layers (for example, the mixture layers 2a, 2b, 2c in FIG. 1). The _{larger the difference between X max} and X _min , the larger the slope ΔX of the volume ratio.

The value of ΔX is, for example, 0.3 or more, may be 0.31 or more, or may be 0.32 or more. On the other hand, the value of ΔX is, for example, 0.5 or less, 0.46 or less, or 0.45 or less.

X _max is, for example, 0.5 or more, and may be 0.6 or more. If X _max is too small, sufficient capacity may not be obtained. On the other hand, X _max may be, for example, 1 or less, 0.9 or less, or 0.8 or less. If X _max is too large, the ion conduction path in the mixture layer may be insufficient.

X _min is, for example, 0.3 or more, and may be 0.4 or more. If X _min is too small, sufficient capacity may not be obtained. On the other hand, X _min is, for example, 0.8 or less, may be 0.6 or less, or may be 0.55 or less. If X _min is too large, the ion conduction path in the mixture layer may be insufficient.

X _ave is, for example, 0.4 or more, and may be 0.5 or more. On the other hand, X _ave is, for example, 0.8 or less, and may be 0.7 or less.

The active material contained in the mixture layer may be a positive electrode active material or a negative electrode active material. Examples of the positive electrode active material include an oxide active material and a sulfur active material. The positive electrode active material is preferably capable of reacting with, for example, Li ions. Examples of the oxide active material include rock salt layered active materials _{such as LiCoO 2} , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O _{2 , and LiMn 2} O ₄ and Li ₄ Examples thereof include spinel-type active materials such as Ti ₅ O ₁₂ and Li (Ni _0.5 Mn _1.5 ) O ₄ , and olivine-type active materials such as _{LiFePO 4} , LiMnPO ₄ , LiNiPO ₄ , and LiCoPO _4. Further, a coat layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte can be suppressed.

On the other hand, examples of the negative electrode active material include a metal active material and a carbon active material. The negative electrode active material is preferably capable of reacting with, for example, Li ions. Examples of the metal active material include elemental metals, metal alloys, and metal oxides. Examples of the metal element contained in the metal active material include Li, Si, Sn, In, and Al. The metal alloy is preferably an alloy containing the above metal element as a main component. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.

Examples of the solid electrolyte contained in the mixture layer include an inorganic solid electrolyte. Examples of the inorganic solid electrolyte include a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, and a halide solid electrolyte. Further, the inorganic solid electrolyte preferably has, for example, Li ion conductivity.

Examples of the sulfide solid electrolyte include Li element, X element (X is at least one of P, Si, Ge, Sn, B, Al, Ga, and In), and a solid electrolyte containing S element. Can be mentioned. Further, the sulfide solid electrolyte may further contain a halogen element. Examples of the oxide solid electrolyte include Li element, Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O element. Examples thereof include solid electrolytes containing. As the nitride-based solid electrolyte, for example, Li ₃ N, and examples of the halide solid electrolyte, for example LiCl, LiI, include LiBr.

The total ratio of the active material and the solid electrolyte in the mixture layer is, for example, 70% by volume or more, 80% by volume or more, or 90% by volume or more.

The mixture layer may further contain at least one of a conductive material and a binder. Examples of the conductive material include carbon materials such as acetylene black (AB) and Ketjen black (KB). On the other hand, examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVdF).

The thickness of the first electrode layer (total thickness of the plurality of mixture layers) is, for example, 0.1 μm or more, may be 1 μm or more, or may be 10 μm or more. On the other hand, the thickness of the first electrode layer (total thickness of the plurality of mixture layers) is, for example, 300 μm or less, and may be 100 μm or less.

2. 2. First Current Collector The first current collector in the present disclosure may be a positive electrode current collector or a negative electrode current collector. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel and carbon.

Examples of the shape of the first current collector include a foil shape and a mesh shape. Further, the thickness of the first current collector is, for example, 0.1 μm or more, and may be 1 μm or more. On the other hand, the thickness of the first current collector is, for example, 300 μm or less, and may be 100 μm or less. Further, the battery case may also have the function of the first current collector.

3. 3. Solid Electrolyte Layer The solid electrolyte layer in the present disclosure is a layer containing a solid electrolyte, and may further contain a binder. Since the solid electrolyte and the binder are the same as those described in "1. First electrode layer" above, the description thereof is omitted here.

The thickness of the solid electrolyte layer is, for example, 0.1 μm or more, may be 1 μm or more, or may be 10 μm or more. On the other hand, the thickness of the solid electrolyte layer is, for example, 300 μm or less, and may be 100 μm or less.

4. Second Electrode Layer The second electrode layer in the present disclosure may be a positive electrode layer or a negative electrode layer. When the first electrode layer is a positive electrode layer, the second electrode layer is a negative electrode layer, and when the first electrode layer is a negative electrode layer, the second electrode layer is a positive electrode layer. Since the positive electrode layer and the negative electrode layer are the same as those described in "1. First electrode layer" above, the description thereof is omitted here.

Further, the second electrode layer may have a laminated structure in which a plurality of mixture layers containing an active material and a solid electrolyte are laminated. In this case, both the first electrode layer and the second electrode layer have a laminated structure.

When the volume ratio of the active material to the solid electrolyte in the mixture layer is Y, the volume ratio Y is toward the solid electrolyte layer from the second current collector in the plurality of mixture layers. May be reduced.

When the inclination of the volume ratio defined by the following formula is ΔY, the ΔY may satisfy 0.3 ≦ ΔY ≦ 0.5.
Slope ΔY = (Y _max −Y _min ) / Y _ave
(In the formula, Y _max is the volume ratio in the mixture layer closest to the second current collector, and Y _min is the volume ratio in the mixture layer closest to the solid electrolyte layer, and Y _ave. Is the average of the volume ratios in the plurality of composite layers)

The preferred ranges of ΔY, Y _max , Y _min and _Yave are the same as the preferred ranges of ΔX, X _max , X _min and X _ave described above, respectively, and thus the description thereof is omitted here.

The thickness of the second electrode layer is, for example, 0.1 μm or more, may be 1 μm or more, or may be 10 μm or more. On the other hand, the thickness of the second electrode layer is, for example, 300 μm or less, and may be 100 μm or less.

5. Second Current Collector The second current collector in the present disclosure may be a positive electrode current collector or a negative electrode current collector. When the first collector is a positive electrode collector, the second collector is a negative electrode collector, and when the first collector is a negative electrode collector, the second collector is a positive electrode collector. It becomes. Since the positive electrode current collector and the negative electrode current collector are the same as those described in "2. First current collector" above, the description thereof is omitted here.

Examples of the shape of the second current collector include a foil shape and a mesh shape. The thickness of the second current collector is, for example, 0.1 μm or more, and may be 1 μm or more. On the other hand, the thickness of the second current collector is, for example, 300 μm or less, and may be 100 μm or less. Further, the battery case may also have the function of the second current collector.

6. All-solid-state battery The all-solid-state battery in the present disclosure is preferably an all-solid-state lithium-ion battery. Further, the all-solid-state battery may be a primary battery or a secondary battery, but a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful as an in-vehicle battery, for example. Further, the all-solid-state battery may be a battery having one power generation element having a positive electrode layer, a solid electrolyte layer and a negative electrode layer, or a battery having a plurality of power generation elements. In the latter case, the all-solid-state battery may be a battery in which a plurality of power generation elements are connected in parallel, or a battery in which a plurality of power generation elements are connected in series. Further, adjacent power generation elements may share a current collector.

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any one having substantially the same structure as the technical idea described in the claims of the present disclosure and having the same effect and effect is the present invention. Included in the technical scope of the disclosure.

[Comparative Example 1]
(Preparation of positive electrode mixture)
As the positive electrode material, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (positive electrode active material), sulfide glass containing Li element, P element and S element (solid electrolyte), Showa Denko VGCF-H ( Conductive material) was used. These materials were weighed and mixed at a volume ratio of X = 0.6 at positive electrode active material: solid electrolyte: conductive material = X: (1-X): 0.04. To 2 g of the obtained mixture, 3 mL of heptane was added and crushed with an ultrasonic homogenizer to prepare a slurry. The obtained slurry was dried at 100 ° C. for 2 hours to obtain a positive electrode mixture having a volume ratio X of the positive electrode active material to the solid electrolyte of 0.6.

(Making negative electrode mixture)
As the negative electrode material, Si (negative electrode active material), sulfide glass (solid electrolyte) containing Li element, P element and S element, and VGCF-H (conductive material) manufactured by Showa Denko were used. These materials were weighed in a volume ratio of negative electrode active material: solid electrolyte: conductive material = 0.55: 0.45: 0.054 and mixed. To 2 g of the obtained mixture, 3 mL of heptane was added and crushed with an ultrasonic homogenizer to prepare a slurry. The obtained slurry was dried at 100 ° C. for 2 hours to obtain a negative electrode mixture.

(Preparation of evaluation cell)
108 mg of the positive electrode mixture was weighed, placed in a cylinder made of Macol, and pressed at 1 ton to obtain positive electrode pellets. A battery pellet was obtained by putting 30 mg of sulfide glass and 26 mg of a negative electrode mixture on the obtained positive electrode pellets and pressing them in order at 1 ton. Both ends of the obtained battery pellet were sandwiched between SUS pins and restrained at 6.0 Nm with bolts to obtain an evaluation cell with a design capacity of 12 mAh. Since the positive electrode layer of the obtained evaluation cell has a single layer structure, the inclination degree ΔX is 0.

[Comparative Example 2]
A positive electrode mixture A was obtained in the same manner as in Comparative Example 1 except that the volume ratio was changed to X = 0.7. Similarly, the positive electrode mixture B was obtained in the same manner as in Comparative Example 1 except that the volume ratio was changed to X = 0.55. An evaluation cell was obtained in the same manner as in Comparative Example 1 except that a positive electrode layer having a two-layer structure was produced using the positive electrode mixture A and B. The volume ratio of the positive electrode active material in the positive electrode mixture A _{corresponds to X max,} and the volume ratio of the positive electrode active material in the positive electrode mixture B corresponds to _{X min. Further, X ave} was obtained from the amounts of the positive electrode mixture A and B used. The degree of inclination ΔX is (0.7-0.55) /0.63=0.24.

[Examples 1 to 4, Comparative Examples 3 and 4]
Positive electrode mixture A and B were obtained in the same manner as in Comparative Example 2 except that the volume ratio of the positive electrode active material was changed to the value shown in Table 1. Further, an evaluation cell was obtained in the same manner as in Comparative Example 2 except that the amounts of the obtained positive electrode mixture A and B used _{were adjusted so as to obtain X ave shown in Table 1.} The design capacity of each evaluation cell was set to 12 mAh.

[evaluation]
Charge / discharge tests were performed on the evaluation cells obtained in Examples 1 to 4 and Comparative Examples 1 to 4. The test conditions were a temperature of 25 ° C. and a voltage range of 3.0 V to 4.25 V. The C rate was 0.1C or 2C. The results of the charge capacity are shown in Table 1 and FIG.

As shown in Table 1, when charging at 0.1 C, each evaluation cell showed a set capacity of 12 mAh. On the other hand, when charging at 2C, a difference in charging capacity was observed depending on the evaluation cell. Specifically, as shown in Table 1 and FIG. 2, it was confirmed that the charging capacity of Examples 1 to 4 was significantly increased as compared with Comparative Examples 1 to 4. In particular, in Example 3, the charging capacity was improved by about 2.5 times or more as compared with Comparative Example 4. That is, it was confirmed that the charging capacity at a high rate specifically increases when the inclination ΔX is 0.3 or more and 0.5 or less.

The reason why the charging capacities at high rates are about the same in Comparative Examples 1 and 2 is that the inclination ΔX in Comparative Example 2 is too small, and the positive electrode layer (positive electrode layer having a two-layer structure) in Comparative Example 2 is Comparative Example 1. It is presumed that this is because the structure is almost the same as that of the positive electrode layer (single-layer structure positive electrode layer) in. Further, the reason why the charge capacity at a high rate is small in Comparative Examples 1 and 2 is that the volume ratio of the positive electrode active material in the mixture layer adjacent to the solid electrolyte layer (the mixture layer using the positive electrode mixture B) is high. It is assumed that the Li ion conduction path in the composite layer may be insufficient. On the other hand, the reason why the charge capacity at a high rate is small in Comparative Examples 3 and 4 is that the inclination ΔX is too large and the positive electrode in the mixture layer adjacent to the positive electrode current collector (the mixture layer using the positive electrode mixture A) is positive. It is presumed that this is because the volume ratio of the active material becomes too high, and as a result, the Li ion conduction path in the mixture layer is insufficient.

On the other hand, the reason why the charge capacity at a high rate is large in Examples 1 to 4 is that the inclination degree ΔX is within a predetermined range, so that the mixture layer (positive electrode mixture B) adjacent to the solid electrolyte layer is provided. The volume ratio of the positive electrode active material in the used mixture layer) can be made relatively low, and at the same time, the volume of the positive electrode active material in the mixture layer adjacent to the positive electrode current collector (the mixture layer using the positive electrode mixture A). It is presumed that this is because it is possible to suppress the ratio from becoming too high and cause a battery reaction in the entire positive electrode layer.

1 ... 1st current collector 2 ... 1st electrode layer 3 ... Solid electrolyte layer 4 ... 2nd electrode layer 5 ... 2nd current collector 10 ... All-solid-state battery

Claims (1)

An all-solid-state battery having a first current collector, a first electrode layer, a solid electrolyte layer, a second electrode layer, and a second current collector in this order.
The first electrode layer has a laminated structure in which a plurality of mixture layers containing an active material and a solid electrolyte are laminated.
When the volume ratio of the active material to the total of the solid electrolyte and the active material in the mixture layer is X, the volume ratio X is obtained from the first current collector in the plurality of mixture layers. It decreases toward the solid electrolyte layer and
An all-solid-state battery in which ΔX satisfies 0.33 ≦ ΔX ≦ 0.40 when the inclination of the volume ratio defined by the following formula is ΔX.
Inclination ΔX = (X _max −X _min ) / X _ave
(In the formula, X _max is the volume ratio in the mixture layer closest to the first current collector.
X _min is the volume ratio in the mixture layer closest to the solid electrolyte layer, and X _ave is the average of the volume ratios in the plurality of mixture layers).

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