JP7294240B2 - solid state battery - Google Patents

Description

The present application discloses a solid state battery.

Patent Literature 1 discloses a technique for suppressing temperature rise of the battery when the battery is short-circuited by providing a heat absorbing layer or a PPTC film in the solid battery. Specifically, in a solid battery using carbon as a negative electrode active material and a sulfide solid electrolyte as a solid electrolyte, an endothermic layer containing mannitol and calcium sulfate dihydrate, and a PPTC film containing furnace black and PVDF and are arranged.

JP 2018-010848 A

In some cases, Si is used as a negative electrode active material to increase battery capacity. On the other hand, according to the findings of the present inventors, Si easily generates heat at a low temperature (for example, about 160 to 220° C.) compared to carbon. Therefore, in a solid-state battery using Si as a negative electrode active material, when the temperature of the battery rises due to a short circuit or the like, the heat-absorbing layer and the PPTC film as disclosed in Patent Document 1 reach a temperature at which they exhibit sufficient functions. There is a possibility that Si will generate heat before the heat is applied, and it is difficult to suppress an increase in the amount of heat generated by the battery.

As one means for solving the above problems, the present application provides
A positive electrode active material layer, a negative electrode active material layer, a solid electrolyte layer, and a polymer electrolyte layer,
The solid electrolyte layer is arranged between the positive electrode active material layer and the negative electrode active material layer,
the polymer electrolyte layer is disposed between at least one of between the positive electrode active material layer and the solid electrolyte layer and between the negative electrode active material layer and the solid electrolyte layer;
The negative electrode active material layer contains Si as a negative electrode active material,
The solid electrolyte layer contains an inorganic solid electrolyte having Li as a constituent element,
The polymer electrolyte layer has an ionic conductivity at 120°C that is lower than that at 60°C.
A solid state battery is disclosed.

The polymer electrolyte layer provided in the solid-state battery of the present disclosure has an ionic conductivity at 120°C lower than that at 60°C. Therefore, for example, when the temperature of the battery rises due to a short circuit or the like, the ionic conductivity of the polymer electrolyte layer decreases before reaching the temperature at which Si heat generation occurs, and the battery reaction can be suppressed and the battery generates heat. can be suppressed. That is, even if the temperature of the solid battery of the present disclosure rises due to a short circuit or the like, it is difficult for the temperature to reach the temperature at which Si generates heat, and it is easy to suppress an increase in the amount of heat generated by Si heat generation.

1 is a schematic diagram for explaining an example of the configuration of a solid-state battery 100; FIG. FIG. 4 is a diagram comparing DSC heat generation data of a negative electrode mixture A containing Si and DSC heat generation data of a negative electrode mixture B containing C; 4 is a graph showing the temperature dependence of ionic conductivity for polymer solid electrolyte materials employed in solid-state batteries according to Examples. FIG. 4 is a schematic diagram for explaining conditions of an internal short-circuit test; 4 is a graph comparing the highest temperature reached during an internal short-circuit test between a solid-state battery according to an example and a solid-state battery according to a comparative example.

As shown in FIGS. 1A to 1D, the solid battery 100 includes a positive electrode active material layer 10, a negative electrode active material layer 20, a solid electrolyte layer 30, and a polymer electrolyte layer . The solid electrolyte layer 30 is arranged between the positive electrode active material layer 10 and the negative electrode active material layer 20 . The polymer electrolyte layer 40 is arranged at least one of between the positive electrode active material layer 10 and the solid electrolyte layer 30 and between the negative electrode active material layer 20 and the solid electrolyte layer 30 . The negative electrode active material layer 20 contains Si as a negative electrode active material. The solid electrolyte layer 30 contains an inorganic solid electrolyte having Li as a constituent element. The polymer electrolyte layer 40 has an ionic conductivity at 120°C lower than that at 60°C.

1. Positive Electrode Active Material Layer The positive electrode active material layer 10 contains at least a positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer 10 may optionally contain a solid electrolyte, a binder, a conductive aid, and the like. A known active material may be used as the positive electrode active material. Among known active materials, two substances having different potentials (charge/discharge potentials) at which predetermined ions are occluded and released are selected. Each can be used as a negative electrode active material. Specific examples of the positive electrode active material include various lithium-containing oxides such as lithium cobalt oxide, lithium nickel oxide, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , lithium manganate, and lithium iron phosphate. are mentioned. A coating layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer may be provided on the surface of the positive electrode active material in order to suppress reaction due to contact between the positive electrode active material and the solid electrolyte. Examples of solid electrolytes that can be included in the positive electrode active material layer 10 include inorganic solid electrolytes and polymer electrolytes. Inorganic solid electrolytes have higher ionic conductivity than polymer electrolytes. In addition, it has excellent heat resistance compared to polymer electrolytes. Preferred inorganic solid electrolytes include oxide solids such as lithium lanthanum zirconate, LiPON, Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ , Li—SiO glass, Li—Al—S—O glass, and the like. Electrolyte; Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Si ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ —LiI—LiBr , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ -GeS ₂ and other sulfides A solid electrolyte can be exemplified. In particular, a sulfide solid electrolyte containing Li and S as constituent elements is preferred, and a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ is more preferred. Examples of binders that can be contained in the positive electrode active material layer 10 include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, polyvinylidene fluoride (PVdF) binders, polytetra Examples include fluoroethylene (PTFE) binders. Examples of conductive aids that can be contained in the positive electrode active material layer 10 include carbon materials such as acetylene black and Ketjenblack, and metal materials such as nickel, aluminum, and stainless steel. The content of each component in the positive electrode active material layer 10 may be the same as the conventional one. The shape of the positive electrode active material layer 10 may also be the same as the conventional one. The positive electrode active material layer 10 may be in the form of a sheet from the viewpoint of facilitating the construction of the solid battery 100 . The thickness of the positive electrode active material layer 10 is not particularly limited. For example, it may be 0.1 μm or more and 2 mm or less. The lower limit may be 1 μm or more, and the upper limit may be 1 mm or less.

2. Negative Electrode Active Material Layer The negative electrode active material layer 20 contains at least Si as a negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer 20 may optionally contain a solid electrolyte, a binder, a conductive aid, and the like. The negative electrode active material contained in the negative electrode active material layer 20 may consist of only Si, or may contain Si and a negative electrode active material other than Si. Si may be Si alone or Si alloy. A known active material may be used as the negative electrode active material other than Si. For example, silicon-based active materials other than Si such as silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium and lithium alloys. The solid electrolyte, the binder, and the conductive aid can be appropriately selected and used from those exemplified as those used for the positive electrode active material layer 10 . The content of each component in the negative electrode active material layer 20 may be the same as the conventional one. The shape of the negative electrode active material layer 20 may also be the same as the conventional one. From the viewpoint that the solid battery 100 can be configured more easily, the negative electrode active material layer 20 may be in the form of a sheet. The thickness of the negative electrode active material layer 20 is not particularly limited. For example, it may be 0.1 μm or more and 2 mm or less. The lower limit may be 1 μm or more, and the upper limit may be 1 mm or less. The thickness and lamination area (electrode area) of the negative electrode active material layer 20 may be adjusted so that the capacity of the negative electrode is larger than the capacity of the positive electrode.

3. Solid Electrolyte Layer The solid electrolyte layer 30 is arranged between the positive electrode active material layer 10 and the negative electrode active material layer 20 . The solid electrolyte layer 30 may contain an inorganic solid electrolyte and optionally a binder. The inorganic solid electrolyte has Li as a constituent element. The inorganic solid electrolyte and binder that can be contained in the solid electrolyte layer 30 can be appropriately selected and used from various inorganic solid electrolytes and binders exemplified as those used in the positive electrode active material layer 10 . For example, it may be a sulfide solid electrolyte having Li and S as constituent elements. The content of each component in the solid electrolyte layer 30 may be the same as the conventional one. The shape of the solid electrolyte layer 30 may also be the same as the conventional one. The solid electrolyte layer 30 may be a sheet-like solid electrolyte layer 30 from the viewpoint of facilitating the construction of the solid battery 100 . The thickness of the solid electrolyte layer 30 may be, for example, 0.1 μm or more and 2 mm or less. The lower limit may be 1 μm or more, and the upper limit may be 1 mm or less.

4. Polymer Electrolyte Layer The polymer electrolyte layer 40 may be disposed between the positive electrode active material layer 10 and the solid electrolyte layer 30 (FIG. 1(A)), or between the negative electrode active material layer 20 and the solid electrolyte layer 30. It may be arranged between them (FIG. 1(B)), or may be arranged between them (FIG. 1(C)). In addition, as shown in FIG. 1D, when the solid electrolyte layer 30 has two or more layers 30a and 30b, between the positive electrode active material layer 10 and the solid electrolyte layer 30b (or the negative electrode active material layer 20) and the solid electrolyte layer 30a). Further, the polymer electrolyte layer 40 may be arranged between the solid electrolyte layer 30 and the layer that generates heat at a lower temperature among the positive electrode active material layer 10 and the negative electrode active material layer 20 .

The polymer electrolyte layer 40 has an ion conductivity (lithium ion conductivity) at 120°C lower than that at 60°C. The ionic conductivity of the polymer electrolyte layer 40 may decrease continuously or intermittently as the temperature rises from 60°C to 120°C. The ionic conductivity may be abruptly lowered in the vicinity. The ionic conductivity of the polymer electrolyte layer 40 at 120° C. may be 50% or less, 40% or less, or 30% or less of the ionic conductivity at 60° C., It may be 20% or less, or 10% or less.

A material forming the polymer electrolyte layer 40 is, for example, a mixture of a polymer, a dopant, and a lithium compound. The material may be a mixture of a reaction mixture obtained by reacting a polymer and a dopant with each other and a lithium compound. By selecting the type of polymer, the type of dopant, and the like, it is possible to configure the polymer electrolyte layer 40 in which the ionic conductivity at 120°C is lower than the ionic conductivity at 60°C. For example, in the findings of the present inventors, polyphenylene sulfide as a polymer and chloranil as a dopant are mixed to form a mixture, the mixture is heated to obtain a reaction mixture, and the reaction mixture and a lithium compound (e.g., LiTFSI, etc.) imide salt), a polymer electrolyte material having an ionic conductivity at 120°C lower than that at 60°C can be obtained. In the polymer electrolyte material thus obtained, the ionic conductivity gradually decreases as the temperature rises from 60°C to 120°C, and the ionic conductivity at 120°C is 10% of the ionic conductivity at 60°C. can go down to

The polymer electrolyte layer 40 may be any material as long as it can suppress ion conduction between the positive electrode active material layer 10 and the negative electrode active material layer 20 when the ion conductivity of the polymer electrolyte layer 40 itself is reduced. The thickness is not particularly limited as long as it is exhibited. The thickness of the polymer electrolyte layer 40 may be, for example, 0.1 μm or more and 2 mm or less. The lower limit may be 1 μm or more, and the upper limit may be 1 mm or less. The polymer electrolyte layer 40 may be thinner or thicker than the solid electrolyte layer 30 . From the viewpoint of ensuring high ionic conductivity at the battery's normal operating temperature, the polymer electrolyte layer 40 should be thinner.

5. Others In addition to the layers 10 to 40 described above, the solid battery 100 may include a positive electrode current collector layer connected to the positive electrode active material layer 10 and a negative electrode current collector layer connected to the negative electrode active material layer 20. good. As the current collector layer, any one commonly used as a current collector layer for batteries can be employed. Further, the solid-state battery 100 may include an endothermic layer or a PPTC film (PPTC layer) as disclosed in Patent Document 1. It is believed that this can further suppress an increase in the amount of heat generated by the battery. In addition, the solid-state battery 100 may include other members and layers such as a terminal, an exterior body, a restraining member, an insulating layer, and a heat insulating layer, if necessary.

Each layer 10 to 40 of the solid-state battery 100 can be produced by, for example, dry molding such as compacting, or wet molding using slurry. The layers 10 to 40 constituting the solid-state battery 100 may be laminated together and optionally subjected to a pressing process to obtain the solid-state battery 100 .

As described above, in the solid battery 100, when the battery temperature rises due to a short circuit or the like, the polymer electrolyte layer The ionic conductivity of 40 is lowered, so that the battery reaction can be suppressed and the heat generation of the battery can be suppressed. That is, even if the temperature of the solid battery 100 rises due to a short circuit or the like, it is difficult for the temperature to reach the temperature at which Si generates heat, and it is easy to suppress an increase in the amount of heat generated due to the heat generated by Si.

1. Confirmation of calorific value of negative electrode material A battery was constructed using negative electrode mixture A composed of Si and a sulfide solid electrolyte. confirmed. Further, a battery was constructed using the negative electrode mixture B containing C and a sulfide solid electrolyte, and after charging to 4.55 V, the negative electrode mixture B was taken out and the exothermic peak temperature was confirmed by DSC. The results are shown in FIG. As shown in FIG. 2, the negative electrode mixture A containing Si has an exothermic peak on the low temperature side (about 160 to 220° C.) compared to the negative electrode mixture B containing C.

2. Confirmation of Effect of Polymer Electrolyte Layer From the results shown in FIG. There is a possibility that heat generation of Si may occur before the process. That is, even if the solid-state battery has a PPTC film or the like, when the temperature of the battery rises due to a short circuit or the like, there is concern that the amount of heat generated by the battery will increase due to the heat generated by Si. The inventor of the present invention came up with the idea of using a polymer electrolyte layer as a countermeasure against Si heat generation. In other words, by arranging a polymer electrolyte layer in the solid battery in which the ionic conductivity decreases before reaching the temperature at which Si generates heat, even if the temperature of the solid battery rises due to a short circuit or the like, the heat generated by Si can be prevented. It becomes difficult to reach the temperature at which Si generates, and it is thought that an increase in the amount of heat generated by the battery due to the heat generated by Si can be suppressed. As a result of examining various polymer electrolytes as materials constituting the polymer electrolyte layer, the inventors of the present invention found that in a solid battery, by adopting a polymer electrolyte layer whose ionic conductivity at 120°C is lower than that at 60°C, , it was found that an increase in the amount of heat generated by the battery due to the heat generated by Si can be suppressed. An example of an embodiment is shown below, but the configuration of the solid-state battery of the present disclosure is not limited to the following configuration.

2.1 Examples Solid-state batteries according to Examples were produced using the following materials.

2.1.1 Positive electrode current collector layer Furnace black (manufactured by Tokai Carbon Co., Ltd.) having an average primary particle size of 66 nm and PVDF (manufactured by Kureha Co., Ltd.) were weighed so that the volume ratio was 20:80. was mixed with NMP (manufactured by Nippon Refine Co., Ltd.) to obtain a PPTC film paste. The obtained paste was applied to the surface of an Al foil (10 μm thick) and dried at 100° C. for 1 hour to provide a PPTC film (10 μm thick) on the surface of the Al foil, which was used as a positive electrode current collector. Using.

2.1.2 Positive Electrode Active Material Layer The positive electrode active material, sulfide solid electrolyte, conductive aid, and binder were mixed in a mass ratio of positive electrode active material:sulfide solid electrolyte:conductive aid:binder=85:13:1. A positive electrode active material layer (thickness: 80 μm) was obtained by weighing and molding so as to have a ratio of 0.3:0.7. LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Sumitomo Metal Mining Co., Ltd.) coated with LiNbO ₃ was used as the positive electrode active material. As a sulfide solid electrolyte, 10LiI-90 (0.75Li ₂ S-0.25P ₂ S ₅ ) was synthesized, crystallized and atomized, and used (10LiI-90 (0.75Li ₂ S- 0.25P ₂ S ₅ ), see JP-A-2012-48973, and crystallization and atomization, see JP-A-2014-102987). Vapor-grown carbon fiber (VGCF, manufactured by Showa Denko KK) was used as the conductive aid. PVDF was used as the binder.

2.1.3 Negative Electrode Active Material Layer The mass ratio of the negative electrode active material, sulfide solid electrolyte, conductive aid, and binder was negative electrode active material:sulfide solid electrolyte:conductive aid:binder=53:41:4. A negative electrode active material layer (thickness: 80 µm) was obtained by weighing and molding so that the ratio was 0.5:1.5. As the negative electrode active material, Si (manufactured by Mitsui Kinzoku Co., Ltd., average particle diameter D ₅₀ =2.5 μm) was used. The sulfide solid electrolyte, conductive aid and binder are the same as those used in the positive electrode active material layer.

2.1.4 Negative Electrode Current Collector Layer Ni foil (10 μm thick) was used as the negative electrode current collector.

2.1.5 Separator Layer A polymer electrolyte material was produced with reference to Example 1 of JP-A-2018-522083. Specifically, polyphenylene sulfide (PPS) as a polymer and chloranil powder as a dopant were mixed in a weight ratio of PPS:chloranil=76:24. The resulting mixture was heated at 350° C. for 24 hours in an air atmosphere to obtain a reaction mixture. The resulting reaction mixture and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were mixed at a weight ratio of 95:5 to obtain a polymer electrolyte material. The obtained polymer electrolyte material and the binder (PVDF) are mixed in a mass ratio of polymer electrolyte material:binder = 99.4:0.6 to form a polymer electrolyte mixture, and the polymer electrolyte mixture is It was molded to obtain a polymer electrolyte layer (thickness 5 μm). On the other hand, the same sulfide solid electrolyte and binder as described above are mixed so that the mass ratio is 99.6:0.4 to form a solid electrolyte mixture, and the solid electrolyte mixture is molded to form a solid. An electrolyte layer (10 μm thick) was obtained. The resulting polymer electrolyte layer and solid electrolyte layer were laminated together to form a separator layer (thickness: 15 μm).

2.1.6 Solid Battery Using the above layers, it has a layer structure of "positive electrode current collector layer/positive electrode active material layer/polymer electrolyte layer/solid electrolyte layer/negative electrode active material layer/negative electrode current collector layer". A solid battery was obtained. Initial activation (3-4.55 V (CCCV), charge 1/10 C, discharge 2 C, rest condition 1/100 C) was performed on the obtained solid battery, and the initial capacity was confirmed (3-4.35 V ( CCCV), charge 1/3C, discharge 1/3C, rest condition 1/100C, 5 cycles), and then voltage regulation (4.35V, CCCV, charge 1/3C, rest condition 1/100C). Thus, a solid battery according to the example was obtained.

2.2 Comparative Example A solid battery was obtained in the same manner as in Example, except that the structure of the separator layer was changed as follows.

A sulfide solid electrolyte and a binder are mixed at a mass ratio of 99.6:0.4 to form a solid electrolyte mixture, and the solid electrolyte mixture is molded to form a separator layer (thickness: 15 μm). Obtained.

3. Physical Property Evaluation of Polymer Electrolyte Material The temperature dependence of the ionic conductivity of the polymer solid electrolyte material employed in the above examples was confirmed. The results are shown in FIG. As shown in FIG. 3, the polymer solid electrolyte according to the example gradually decreased in ionic conductivity with increasing temperature from 60°C to 120°C, and the ionic conductivity at 120°C decreased to ionic conductivity at 60°C. It can be seen that the conductivity can be reduced to 10% or less.

4. Evaluation of Heat Amount of Battery As shown in FIG. 4, a nail penetration test was performed in which a nail having a diameter of 8 mm and a tip angle of 60° was inserted into the central portion of the solid-state battery at a speed of 25 mm/s. For each of the solid-state batteries according to the examples and the comparative examples, the maximum temperature at the temperature measurement point after being punctured with a nail was measured. The results are shown in FIG. As is clear from the results shown in FIG. 5, the maximum temperature of the solid-state battery according to the example was 144° C. lower than that of the solid-state battery according to the comparative example. As described above, the polymer solid electrolytes used in the examples have an ionic conductivity at 120° C. that is 10% or less of the ionic conductivity at 60° C. Therefore, in the solid batteries according to the examples, the temperature rise It is considered that the resistance of the separator layer increased along with the heat generation, and as a result of the shutdown function working before the heat generation peak temperature of Si was reached, the heat generation of Si in the negative electrode active material layer was suppressed.

The solid-state battery of the present disclosure can be widely used, for example, from small power sources for mobile devices to large power sources for vehicles.

10 positive electrode active material layer 20 negative electrode active material layer 30 solid electrolyte layer 40 polymer electrolyte layer 100 solid battery

Claims (1)

A positive electrode active material layer, a negative electrode active material layer, a solid electrolyte layer, and a polymer electrolyte layer,
The solid electrolyte layer is arranged between the positive electrode active material layer and the negative electrode active material layer,
the polymer electrolyte layer is disposed between at least one of between the positive electrode active material layer and the solid electrolyte layer and between the negative electrode active material layer and the solid electrolyte layer;
The negative electrode active material layer contains Si as a negative electrode active material,
The solid electrolyte layer contains an inorganic solid electrolyte having Li as a constituent element,
The polymer electrolyte layer has an ionic conductivity at 120°C that is lower than that at 60°C.
solid state battery.

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