All-solid lithium ion secondary battery

An all-solid lithium ion secondary battery includes a laminate including a positive electrode layer, a negative electrode layer which is alternately laminated with the positive electrode layer, a solid electrolyte which is interposed at least between the positive electrode layer and the negative electrode layer, and an insulating outermost layer which is positioned at both ends in a lamination direction and does not contain lithium ions.

TECHNICAL FIELD

The present disclosure relates to an all-solid lithium ion secondary battery.

Priority is claimed on Japanese Patent Application No. 2018-002210, filed Jan. 10, 2018, the content of which is incorporated herein by reference.

BACKGROUND ART

Lithium ion secondary batteries are widely used as power supplies for portable small devices, for example, mobile phones, laptops, and PDAs. Lithium ion secondary batteries used for such portable small devices are required to be smaller, thinner and more reliable.

Regarding lithium ion secondary batteries, those in which an organic electrolytic solution is used as an electrolyte and those using a solid electrolyte are known. Compared to a lithium ion secondary battery using an organic electrolytic solution, a lithium ion secondary battery (all-solid lithium ion secondary battery) in which a solid electrolyte is used as an electrolyte has a higher degree of freedom in design of the shape of the battery, and a small-sized and thin battery can be easily obtained. In addition, the all-solid lithium ion secondary battery has an advantage of high reliability without leaking of an electrolytic solution.

In addition, the all-solid lithium ion secondary battery is nonflammable. Accordingly, the all-solid lithium ion secondary battery has an advantage that it can be mounted on a substrate by reflow soldering like other electronic components.

For example, Patent Literature 1 describes an all-solid lithium ion secondary battery in which lithium titanium aluminum phosphate is used for a solid electrolyte layer.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the all-solid lithium ion secondary battery described in Patent Literature 1 tends to self-discharge at a certain 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 lithium ion secondary battery that can curb self-discharging.

Solution to Problem

The inventors conducted extensive studies in order to address the above problems.

As a result, the inventors have found the following points. That is, in the related art, it was thought that both ends of a positive electrode layer and a negative electrode layer in a lamination direction had no influence on performance of the all-solid lithium ion secondary battery. However, the inventors found that, when a solid electrolyte containing Li ions is present at both ends of the positive electrode layer and the negative electrode layer in the lamination direction, the lithium ions move unintentionally and as a result, self-discharging may occur. This is thought to have been caused by the fact that, unlike a capacitor which uses an original insulating dielectric material, a solid electrolyte has ion conductivity, and lithium ions move inside the solid electrolyte.

As shown inFIG.3, in the technology described in Patent Literature 1, a solid electrolyte3containing lithium titanium aluminum phosphate is provided at both ends of a positive electrode layer1and a negative electrode layer2in a lamination direction. Therefore, self-discharging may occur at a certain rate.

In order to solve the above problems, the following aspects are provided.

(1) An all-solid lithium ion secondary battery according to a first aspect includes a laminate including

a positive electrode layer;

a negative electrode layer which is alternately laminated with the positive electrode layer;

a solid electrolyte which is interposed at least between the positive electrode layer and the negative electrode layer; and

an insulating outermost layer which is positioned at both ends in a lamination direction and does not contain lithium ions.

(2) In the all-solid lithium ion secondary battery according to the above aspect, the outermost layer may contain Si and one of B and Ba.

(3) In the all-solid lithium ion secondary battery according to the above aspect, a first external terminal and a second external terminal may be formed in contact with side surfaces of the laminate, the positive electrode layer may be connected to the first external terminal and the negative electrode layer may be connected to the second external terminal, and an insulation layer made of the same material as the outermost layer may be formed so that it surrounds a side surface that is not connected to the first external terminal of the positive electrode layer and a side surface that is not connected to the second external terminal of the negative electrode layer in a plan view.
(4) In the all-solid lithium ion secondary battery according to the above aspect, the outermost layer may be a glass sintered component having a softening temperature of 500° C. to 900° C.
(5) In the all-solid lithium ion secondary battery according to the above aspect, the outermost layer may be a sintered component of an insulator raw material having a coefficient of thermal expansion of 50×10−7/° C. or higher.

Advantageous Effects of Invention

According to the aspects, it is possible to provide an all-solid lithium ion secondary battery that can curb self-discharging.

DESCRIPTION OF EMBODIMENTS

The present disclosure will be appropriately described below in detail with reference to the drawings. In the drawings used in the following description, in order to facilitate understanding of features of the present disclosure, feature parts are enlarged for convenience of illustration in some cases. Therefore, ratios between sizes and the like of components illustrated in the drawings may be different from those of actual components. Materials, sizes and the like exemplified in the following description are examples, the present disclosure is not limited thereto, and they can be appropriately changed within a range in which effects thereof are obtained.

FIG.1is a schematic cross-sectional view of an enlarged main part of an all-solid lithium ion secondary battery according to the present embodiment. As shown inFIG.1, an all-solid lithium ion secondary battery10includes a laminate4, a first external terminal5, and a second external terminal6. The first external terminal5and the second external terminal6are formed on side surfaces of the laminate4. The laminate4includes first electrode layers1, second electrode layers2which are alternately laminated with the first electrode layers1, a solid electrolyte3interposed at least between the first electrode layer1and the second electrode layer2, and an insulating outermost layer7which is positioned at both ends in the lamination direction and does not contain Li

Each of the first electrode layers1is connected to the first external terminal5. Each of the second electrode layers2is connected to the second external terminal6. The first external terminal5and the second external terminal6are electrical contacts for the outside.

As shown inFIG.1, the first external terminal5and the second external terminal6are formed to be in contact with side surfaces (exposed end surfaces of the first electrode layer1and the second electrode layer2) of the laminate4.

As described above, the laminate4includes the first electrode layer1, the second electrode layer2, the solid electrolyte3, and the outermost layer7.

One of the first electrode layer1and the second electrode layer2functions as a positive electrode and the other thereof functions as a negative electrode. Hereinafter, in order to facilitate understanding, the first electrode layer1will be referred to as the positive electrode layer1, and the second electrode layer2will be referred to as the negative electrode layer2.

In the laminate4, the positive electrode layer1and the negative electrode layer2are alternately laminated with the solid electrolyte3therebetween. The all-solid lithium ion secondary battery10is charged and discharged when lithium ions are transferred between the positive electrode layer1and the negative electrode layer2with the solid electrolyte3therebetween.

<Positive Electrode Layer and Negative Electrode Layer>

The positive electrode layer1includes a positive electrode current collector layer1A and a positive electrode active material layer1B containing a positive electrode active material. The negative electrode layer2includes a negative electrode current collector layer2A and a negative electrode active material layer2B containing a negative electrode active material.

The positive electrode current collector layer1A and the negative electrode current collector layer2A preferably have high conductivity. Therefore, it is preferable to use, for example, silver, palladium, gold, platinum, aluminum, copper, nickel, or the like for the positive electrode current collector layer1A and the negative electrode current collector layer2A. Among these materials, copper is unlikely to react with a positive electrode active material, a negative electrode active material or a solid electrolyte. Therefore, when copper is used for the positive electrode current collector layer1A and the negative electrode current collector layer2A, the internal resistance of the all-solid lithium ion secondary battery10can be reduced. Here, materials constituting the positive electrode current collector layer1A and the negative electrode current collector layer2A may be the same as or different from each other.

The positive electrode active material layer1B is formed on one surface or both surfaces of the positive electrode current collector layer1A. For example, when the positive electrode layer1is formed as the uppermost layer of the laminate4in the lamination direction between the positive electrode layer1and the negative electrode layer2, there is no opposing negative electrode layer2on the positive electrode layer1positioned on the uppermost layer. In such a case, in the positive electrode layer1positioned on the uppermost layer, the positive electrode active material layer1B may be provided only on one surface on the lower side in the lamination direction or may be provided on both sides.

As in the positive electrode active material layer1B, the negative electrode active material layer2B is also formed on one surface or both surfaces of the negative electrode current collector layer2A. In addition, when the negative electrode layer2is formed as the lowermost layer of the laminate4in the lamination direction between the positive electrode layer1and the negative electrode layer2, the negative electrode active material layer2B in the negative electrode layer2positioned on the lowermost layer may be provided only on one surface on the upper side in the lamination direction or may be provided on both sides.

The positive electrode active material layer1B and the negative electrode active material layer2B contain a positive electrode active material and a negative electrode active material which transfer electrons. In addition, the positive electrode active material layer1B and the negative electrode active material layer2B may contain a conductivity aid, a binding agent, and the like. Preferably, the positive electrode active material and the negative electrode active material can efficiently occlude and release lithium ions.

For the positive electrode active material and the negative electrode active material, for example, a transition metal oxide or transition metal composite oxide is preferably used. Specifically, lithium manganese composite oxide Li2MnMa1-aO3(0.8≤a≤1, Ma=Co, Ni), lithium cobalt oxide (LiCoO2), lithium nickelate (LiNiO2), lithium manganese spinel (LiMn2O4), a composite metal oxide represented by general formula: LiNixCoyMnzO2(x+y+z=1, 0≤x≤1, 0≤y≤1, 0≤z≤1), a lithium vanadium compound (LiV2O), an olivine type LiMbPO4(where, Mb is one or more elements selected from among Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr), lithium vanadium phosphate (Li3V2(PO4)3or LiVOPO4), a Li-rich solid solution represented by Li2MnO3-LiMcO2(Mc=Mn, Co, Ni), lithium titanate (Li4Ti5O12), a composite metal oxide represented by LisNitCouAlvO2(0.9<s<1.3, 0.9<t+u+v<1.1), and the like can be used.

The positive electrode active material and the negative electrode active material may be selected according to the solid electrolyte3to be described below.

For example, when Li1+nAlnTi2-n(PO4)3(0≤n≤0.6) is used for the solid electrolyte3, one or both of LiVOPO4and Li3V2(PO4)3are preferably used for the positive electrode active material and the negative electrode active material. Bonding at the interface between the solid electrolyte3of each of the positive electrode active material layer1B and the negative electrode active material layer2B becomes strong. In addition, a contact area at the interface between the solid electrolyte3and each of the positive electrode active material layer1B and the negative electrode active material layer2B can be widened.

There is no clear distinction between active materials constituting the positive electrode active material layer1B and the negative electrode active material layer2B. Comparing potentials of two compounds, a compound exhibiting a higher potential can be used for the positive electrode active material, and a compound exhibiting a lower potential can be used as the negative electrode active material.

In addition, the positive electrode current collector layer1A and the negative electrode current collector layer2A may contain a positive electrode active material and a negative electrode active material, respectively. The content ratio of the active materials included in the current collector layers is not particularly limited as long as the active materials function as a current collector. For example, the volume ratio of the positive electrode current collector/the positive electrode active material or the negative electrode current collector/the negative electrode active material is preferably in a range of 90/10 to 70/30.

When the positive electrode current collector layer1A and the negative electrode current collector layer2A contain a positive electrode active material and a negative electrode active material, respectively, adhesion between the positive electrode current collector layer1A and the positive electrode active material layer1B and between the negative electrode current collector layer2A and the negative electrode active material layer2B is improved.

The solid electrolyte3is interposed at least between the positive electrode layer1and the negative electrode layer2.

Regarding the solid electrolyte3, a material having low electron conductivity and high lithium ion conductivity is preferably used.

Specifically, for example, it is desirable to select at least one selected from the group consisting of perovskite type compounds such as La0.51Li0.34TiO2.94and La0.5Li0.5TiO3, Lisicon compounds such as Li14Zn(GeO4)4, garnet type compounds such as Li7La3Zr2O2, Nasicon type compounds such as Li1.3Al0.3Ti1.7(PO4)3and Li1.5Al0.5Ge1.5(PO4)3, thio-Lisicon compounds such as Li3.25Ge0.25P0.75S4and Li3PS4, glass compounds such as 50Li4SiO4·50Li3BO3, Li2S—P2S5and Li2O—Li3O5—SiO2, phosphoric acid compounds such as Li3PO4, Li3.5Si0.5P0.5O4and Li2.9PO3.3N0.46, amorphous compounds such as Li2.9PO3.3N0.46(LIPON) and Li3.6Si0.6P0.4O4, and glass ceramics such as Li1.07Al0.69Ti1.46(PO4)3and Li1.5Al0.5Ge1.5(PO4)3.

When a material used as the solid electrolyte3is selected, as will be described below, it is necessary to focus on a combination of materials constituting the outermost layer7.

The outermost layer7is positioned at both ends in the lamination direction and does not contain lithium ions and is insulating.

As shown inFIG.3, in an all-solid lithium ion secondary battery40in the related art, no outermost layer is formed at either of ends of the positive electrode layer1and the negative electrode layer2in the lamination direction, and the solid electrolyte3is present at both ends. The solid electrolyte3contains Li ions. Therefore, a leakage current may be generated when Li ions move to both ends of the positive electrode layer1and the negative electrode layer2in the lamination direction. The all-solid lithium ion secondary battery40in the related art tends to self-discharge due to the generated leakage current.

On the other hand, the outermost layer7according to the present embodiment does not contain lithium ions and has an insulating property. Therefore, since lithium ions do not move in the outermost layer7, no leakage current is generated, and self-discharging can be curbed.

The outermost layer7has an insulating property because the outermost layer7is made of an insulator. The insulator constituting the outermost layer7can be obtained by sintering an insulator raw material such as a glass frit.

Here, in the present embodiment, the insulator indicates a material having a resistance value of 106Ω or more.

Here, R in the above chemical formula represents at least one of the alkaline earth metals Mg, Ca, Sr, and Ba.

The insulator raw material is preferably a glass having a softening temperature (softening point) of 500° C. to 900° C. and more preferably 600° C. to 800° C. That is, the outermost layer7is preferably made of a glass sintered component having a softening temperature (softening point) of 500° C. to 900° C. and more preferably 600° C. to 800° C.

When the above conditions are satisfied, this is preferable because the outermost layer7, the positive electrode layer1, the negative electrode layer2, and the solid electrolyte3can be sintered at the same time when the all-solid lithium ion secondary battery10is produced. That is, the outermost layer7having an excellent insulating property can be obtained even during low temperature sintering, and self-discharging can be curbed.

Here, in the present embodiment, glass indicates an amorphous solid that exhibits a glass transition phenomenon.

The outermost layer7preferably contains Si, and one of B and Ba. When the outermost layer7contains Si and one of B and Ba, this is preferable because, for example, sintering is possible at a low temperature, it becomes a material having an excellent insulating property even if simultaneous sintering with the laminate4is performed, and self-discharging can be further curbed.

In order for the outermost layer7to contain Si and one of B and Ba, regarding the insulator raw material, for example, SiO2·B2O3, Bi2O3·B2O3·SiO2, SiO2·BaO·B2O3, SiO2·BaO·ZnO, BaO·SiO2·ZnO, SiO2·B2O3·BaO, ZnO·B2O3·SiO2, BaO·SiO2·B2O3, RO·B2O3·SiO2, SiO2·BaO·Li2O, SiO2·R2O·BaO or the like may be used.

The insulator constituting the outermost layer7preferably has crystallinity. When the insulator constituting the outermost layer7has crystallinity, since the density increases, the mechanical strength of the outermost layer7increases. Therefore, it is possible to reduce a likelihood of the outermost layer7cracking due to the change in the volume resulting from charging and discharging of the battery. In addition, since the outermost layer7having an excellent insulating property can be obtained even if charging and discharging are repeated, self-discharging can be further reduced.

The outermost layer7is preferably composed of a sintered component (insulator) obtained by mixing two or more insulator raw materials and firing the mixture. When insulator raw materials are suitably mixed, it is possible to adjust adhesion between the outermost layer7and other layers (the positive electrode layer1, the negative electrode layer2, and the solid electrolyte3) and the coefficient of thermal expansion of the all-solid lithium ion secondary battery10. Therefore, it is possible to minimize abnormalities of the appearance such as peeling off or cracking of the all-solid lithium ion secondary battery10. In addition, it is preferable to mix insulator raw materials suitably because a material having an excellent insulating property can be obtained even at low temperature sintering.

Examples of mixtures of insulator raw materials include a mixture of Bi2O3·B2O3·SiO2:SiO2·BaO·CaO=50:50, a mixture of Bi2O3·B2O3·SiO2:SiO2B2O3RO=50:50, and a mixture of SiO2·BaO·CaO:SiO2·B2O3·RO=50:50.

The ratio and combination of insulator raw materials can be appropriately determined according to desired performance.

The coefficient of thermal expansion of the insulator raw material is preferably 50×10−7/° C. or higher, and more preferably 60×10−7/° C. or higher and 80×10−7/° C. or lower. That is, the outermost layer7is preferably made of a sintered component of an insulator raw material having a coefficient of thermal expansion of 50×10−7/° C. or higher, and more preferably 60×10−7/° C. or higher and 80×10−7/° C. or lower.

When the coefficient of thermal expansion of the insulator raw material is 50×10−7/° C. or higher, a difference in the coefficient of thermal expansion between the outermost layer7and other layers (the positive electrode layer1, the negative electrode layer2, and the solid electrolyte3) becomes smaller. Therefore, it is possible to reduce cracking due to the difference in thermal expansion and it is possible to obtain the outermost layer7having an excellent insulating property even after charging and discharging are repeated, and thus self-discharging can be further curbed.

As described above, it is necessary to focus on a combination of a material used as the solid electrolyte3and an insulator (insulator raw material) constituting the outermost layer7. In consideration of a combination of both, the following combinations are preferable. Regarding the solid electrolyte3, a Nasicon type compound such as Li1.3Al0.3Ti1.7(PO4)3is used. SiO2·B2O3·RO is used as an insulator raw material which is a raw material of the insulator constituting the outermost layer7. This combination is suitable for production because firing temperatures of both are compatible. In addition to this, it is possible to prevent components of a glass material used for the outermost layer7from diffusing into the laminate4during sintering.

FIG.1shows a case in which the outermost layer7is in contact with the positive electrode layer1. However, the outermost layer7may be provided at both ends in the lamination direction and other points are not particularly limited. That is, one end of the outermost layer7may be in contact with the positive electrode layer1and the other end thereof may be in contact with the negative electrode layer2. The outermost layer7may be in contact with any of the positive electrode layer1and the negative electrode layer2. The outermost layer7may be in contact with neither of the positive electrode layer1nor the negative electrode layer2.

A contact mode between the outermost layer7and the solid electrolyte3is not particularly limited. As shown inFIG.1, a part of one surface of the outermost layer7may be in contact with the solid electrolyte3. As shown inFIG.2, the entire one surface of the outermost layer7may be in contact with the solid electrolyte3.

The all-solid lithium ion secondary battery10includes the first external terminal5and the second external terminal6.

In addition, the first external terminal5and the second external terminal6are electrically connected to electrodes (not shown) provided on a substrate (not shown).

The first external terminal5and the second external terminal6of the all-solid lithium ion secondary battery10are preferably made of a material having high conductivity. For example, silver, gold, platinum, aluminum, copper, tin, and nickel can be used. The first external terminal5and the second external terminal6may be a single layer or a plurality of layers.

In addition, the all-solid lithium ion secondary battery10may include the laminate4and protective layers (not shown) for electrically, physically, and chemically protecting the terminals on the outer circumference of the laminate4.

As a material constituting the protective layer, one that has an excellent insulating property, durability, and humidity resistance and is environmentally safe, is preferable. For example, glass, ceramics, a thermosetting resin or a photocurable resin is preferably used. Materials of the protective layer may be used alone or a plurality thereof may be used in combination. In addition, the protective layer may be a single layer, but a plurality of protective layers are preferable. Among these, an organic-inorganic hybrid in which a thermosetting resin and a ceramic powder are mixed is particularly preferable.

As described above, the all-solid lithium ion secondary battery10according to the present embodiment includes the insulating outermost layer7that does not contain lithium ions at both ends in the lamination direction. Therefore, in the all-solid lithium ion secondary battery10according to the present embodiment, no leakage current is generated and self-discharging can be curbed.

(Method of Producing all-Solid Lithium Ion Secondary Battery)

For a method of producing the all-solid lithium ion secondary battery10, a simultaneous firing method may be used or a sequential firing method may be used.

The simultaneous firing method is a method in which materials for forming layers are laminated and collectively fired to produce a laminate. The sequential firing method is a method of sequentially producing layers, and a firing process is performed whenever a layer is produced. When the simultaneous firing method is used, it is possible to reduce working processes of the all-solid lithium ion secondary battery10. In addition, when the simultaneous firing method is used, the obtained laminate4becomes denser.

Hereinafter, an example in which the all-solid lithium ion secondary battery10shown inFIG.1is produced using the simultaneous firing method will be described.

The simultaneous firing method includes a process of producing a paste of materials constituting the laminate4, a process of applying and drying the paste to produce a green sheet, and a process of laminating the green sheet and simultaneously firing the produced laminated sheet.

First, materials of the positive electrode current collector layer1A, the positive electrode active material layer1B, the solid electrolyte3, the negative electrode active material layer2B, and the negative electrode current collector layer2A, and the outermost layer7which constitute the laminate4are made into pastes.

The material of the outermost layer7includes the above insulator raw materials.

A pasting method is not particularly limited. For example, a paste is obtained by mixing powders of materials in a vehicle. Here, the vehicle is a general term for a medium in a liquid phase. The vehicle includes a solvent and a binder. According to such a method, a paste for the positive electrode current collector layer1A, a paste for the positive electrode active material layer1B, a paste for the solid electrolyte3, a paste for the negative electrode active material layer2B, a paste for the negative electrode current collector layer2A, and a paste for the outermost layer7are produced.

Next, a green sheet is produced. The green sheet is obtained by applying the produced pastes to a substrate such as polyethylene terephthalate (PET) in a desired order, performing drying as necessary, and then peeling off the substrate. A paste applying method is not particularly limited. For example, known methods such as screen printing, application, transferring, and a doctor blade method can be used.

In the present embodiment, the outermost layer7is provided at both ends in the lamination direction. Therefore, when a green sheet is produced, first the paste for the outermost layer7is applied. Then, the paste for the positive electrode current collector layer1A, the paste for the positive electrode active material layer1B, the paste for the solid electrolyte3, the paste for the negative electrode active material layer2B, and the paste for the negative electrode current collector layer2A are applied in a desired order and a desired number of layers. Finally, the paste for the outermost layer7is applied again.

As necessary, alignment, cutting and the like are performed to produce a laminate. When a parallel type or serial-parallel type battery is produced, preferably, alignment and lamination are performed so that the end surface of the positive electrode current collector layer and the end surface of the negative electrode current collector layer do not match.

Next, de-binding and firing are performed to produce a sintered component of the laminate.

De-binding and firing can be performed, for example, under a nitrogen atmosphere at a temperature of 600° C. to 1,000° C. A de-binding and firing maintaining time is, for example, 0.1 to 6 hours. Organic components disappear due to the de-binding and firing.

The sintered component may be put into a cylindrical container together with an abrasive material such as alumina and subjected to barrel polishing. Thereby, it is possible to chamfer corners of the laminate. As another method, sandblasting may be performed for polishing. This method is preferable because only a specific part can be cut.

Here, the present disclosure is not limited to the above method, and a mode in which the paste for the positive electrode current collector layer1A, the paste for the positive electrode active material layer1B, the paste for the solid electrolyte3, the paste for the negative electrode active material layer2B, and the paste for the negative electrode current collector layer2A are applied and fired, and the paste for the outermost layer7is then finally applied and fired may be used.

In addition, when a layer to which the paste for the positive electrode layer1is applied and/or a layer to which the paste for the negative electrode layer2is applied are thick, step filling printing may be performed on a step part (a margin area in which no paste is applied) formed between the layer and a layer below the layer. Normally, the material of the solid electrolyte3is used as a material for step filling printing, but in the present embodiment, the material of the outermost layer7may be used as the material for step filling printing.

The first external terminal5and the second external terminal6are attached to the laminate4. The first external terminal5and the second external terminal6are formed so that they are electrically in contact with the positive electrode current collector layer1A and the negative electrode current collector layer2A, respectively. For example, terminals can be formed by performing known methods such as a sputtering method, a dipping method, and a spray coating method on the positive electrode current collector layer1A and the negative electrode current collector layer2A exposed from the side surfaces of the laminate4. When terminals are formed only in predetermined parts, they are formed by performing, for example, masking with tape.

The embodiments of the present disclosure have been described above in detail with reference to the drawings. Configurations and combinations thereof in the embodiments are only examples, and additions, omissions, substitutions, and other modifications of the configurations can be made without departing from the scope of the present disclosure.

FIG.4is a schematic cross-sectional view of an enlarged main part of another example of the all-solid lithium ion secondary battery according to the present embodiment. In addition,FIG.5is a plan view showing an arrangement of the negative electrode layer2and an insulation layer71included in an all-solid lithium ion secondary battery20shown inFIG.4.

The all-solid lithium ion secondary battery20shown inFIG.4andFIG.5is different from the all-solid lithium ion secondary battery10shown inFIG.1in the following points.

That is, in the all-solid lithium ion secondary battery10shown inFIG.1, in a plan view, the material of the solid electrolyte3is filled in so that it surrounds a side surface that is not connected to the first external terminal5of the positive electrode layer1and a side surface that is not connected to the second external terminal6of the negative electrode layer2. Therefore, in the all-solid lithium ion secondary battery10shown inFIG.1, the material of the solid electrolyte3is filled between the positive electrode layer1and the second external terminal6and between the negative electrode layer2and the first external terminal5of the laminate4in a cross-sectional view.

On the other hand, in the all-solid lithium ion secondary battery20shown inFIG.4andFIG.5, in a plan view, the insulation layer71is formed so that it surrounds a side surface that is not connected to the first external terminal5of the positive electrode layer1and a side surface that is not connected to the second external terminal6of the negative electrode layer2. Therefore, in the all-solid lithium ion secondary battery20shown inFIG.4andFIG.5, the insulation layer71is formed between the positive electrode layer1and the second external terminal6and between the negative electrode layer2and the first external terminal5in a laminate41in a cross-sectional view. InFIG.5, the reference numeral22indicates a side surface that is connected to the second external terminal6of the negative electrode layer2, and the reference numeral21indicates a side surface that is not connected to the second external terminal6of the negative electrode layer2. The insulation layer71is made of the same material as the outermost layer7.

In the all-solid lithium ion secondary battery20shown inFIG.4andFIG.5, the same members as those of the all-solid lithium ion secondary battery10shown inFIG.1will be denoted with the same reference numerals, and descriptions thereof will be omitted.

The all-solid lithium ion secondary battery20shown inFIG.4andFIG.5can be produced by, for example, the following method.

That is, as in the above case in which the all-solid lithium ion secondary battery10shown inFIG.1is produced, the paste for the positive electrode current collector layer TA, the paste for the positive electrode active material layer1B, the paste for the solid electrolyte3, the paste for the negative electrode active material layer2B, the paste for the negative electrode current collector layer2A, and the paste for the outermost layer7are produced.

Then, unlike the case in which the all-solid lithium ion secondary battery10shown inFIG.1is produced, application is performed for producing a green sheet using the above paste according to the following method.

First, the paste for the outermost layer7is applied and the paste for the positive electrode layer1is applied. More specifically, after the paste for the outermost layer7is applied, the paste for the positive electrode active material layer1B, the paste for the positive electrode current collector layer TA, and the paste for the positive electrode active material layer1B are applied in this order. Next, the paste for the outermost layer7serving as the insulation layer71is applied to a step part (a margin area in which no paste for the positive electrode layer1is applied) formed between the paste for the positive electrode layer1and the paste for the outermost layer7applied first so that the step is filled. The step part formed between the paste for the positive electrode layer1and the paste for the outermost layer7applied first is formed in a part serving as a side surface that is not connected to the first external terminal5of the positive electrode layer1.

Next, the paste for the solid electrolyte3is applied and the paste for the negative electrode layer2is applied. More specifically, after the paste for the solid electrolyte3is applied, the paste for the negative electrode active material layer2B, the paste for the negative electrode current collector layer2A, and the paste for the negative electrode active material layer2B are applied in this order. Next, the paste for the outermost layer7serving as the insulation layer71is applied to a step part (a margin area in which no paste for the negative electrode layer2is applied) formed between the paste for the negative electrode layer2and the paste for the solid electrolyte3so that the step is filled. The step part formed between the paste for the negative electrode layer2and the paste for the solid electrolyte3is formed in a part serving as the side surface21that is not connected to the second external terminal6of the negative electrode layer2shown inFIG.5.

Then, in the same manner as described above, the paste for the solid electrolyte3, the paste for the positive electrode layer1, the paste for the negative electrode layer2, and the paste for the outermost layer7serving as the insulation layer71are applied in a desired order and a desired number of layers, and finally the paste for the outermost layer7is applied again.

Then, the same processes as in production of the all-solid lithium ion secondary battery10shown inFIG.1are performed, and thus the all-solid lithium ion secondary battery20shown inFIG.4andFIG.5is obtained.

In the all-solid lithium ion secondary battery20shown inFIG.4andFIG.5, the insulation layer71made of an insulating material which does not contain lithium ions is formed so that it surrounds a side surface that is not connected to the first external terminal5of the positive electrode layer1and a side surface that is not connected to the second external terminal6of the negative electrode layer2in a plan view. Therefore, in the all-solid lithium ion secondary battery20shown inFIG.4andFIG.5, a leakage current is less likely to be generated and self-discharging is further curbed.

EXAMPLES

Examples 1 to 12

The laminate4having the configuration shown inFIG.1was produced by the simultaneous firing method. The structure of layers was as follows.

The positive electrode current collector layer1A and the negative electrode current collector layer2A: Cu+Li3V2(PO4)3

The positive electrode active material layer1B and the negative electrode active material layer2B: Li3V2(PO4)3

The solid electrolyte3and the outermost layer7: As shown in Table 1

The temperature during simultaneous firing was 800° C., and the firing time was 1 hour.

In the laminates4of Examples 1 to 12, in a plan view, the solid electrolyte3was formed so that it surrounded a side surface that was not connected to the first external terminal5of the positive electrode layer1and a side surface that was not connected to the second external terminal6of the negative electrode layer2.

Here, in Table 1, (100%) means that the outermost layer7was composed of only an insulator obtained by sintering the insulator raw materials. In addition, in Table 1, when two insulator raw materials are listed, this means that the outermost layer7was made of an insulator obtained by sintering two insulator raw materials. 50%/50% means that two insulator raw materials were mixed at a ratio of 50%:50%.

Copper was produced on both ends of the laminate4by sputtering and its surface was subjected to nickel plating and tin plating, and the first external terminal5and the second external terminal6were produced.

Table 1 shows the softening point of the insulator raw materials constituting the outermost layer7.

Table 1 shows the coefficient of thermal expansion of the insulator materials used for the outermost layer7.

Next, performances of the all-solid lithium ion secondary batteries produced as described above were evaluated. Specifically, when the voltage was limited to 0 to 1.6 V, the all-solid lithium ion secondary battery was charged, and the residual voltage after 24 hours from charging was measured. Here, a larger residual voltage value indicates that no self-discharging occurred. A smaller residual voltage value indicates that self-discharging occurred.

The residual voltage after 24 hours is shown in Table 1.

Comparative Examples 1 to 3

Comparative Examples 1 to 3 were comparative examples in which the outermost layer7was not provided. That is, like the all-solid lithium ion secondary battery40shown inFIG.3, the outermost layer7was not provided at both ends of the positive electrode layer1and the negative electrode layer2in the lamination direction, and the solid electrolyte3was provided.

Here, in Table 1, the underlined column in the outermost layer of Comparative Examples 1 to 3 indicates that requirements of the present disclosure were not satisfied.

As shown in Table 1, in Comparative Examples 1 to 3, the residual voltage after 24 hours was significantly lower than that in Examples 1 to 12. This is thought to have been caused by the fact that, since no outermost layer7was formed in Comparative Examples 1 to 3, self-discharging occurred. This is thought to have been the cause of the residual voltage after 24 hours decreasing in Comparative Examples 1 to 3.

Examples 13 to 24

The laminate41having the configuration shown inFIG.4andFIG.5was produced by the simultaneous firing method. The structure of layers was as follows.

The positive electrode current collector layer1A, the negative electrode current collector layer2A, the positive electrode active material layer1B, and the negative electrode active material layer2B: as shown in Example 1 The solid electrolyte3, the outermost layer7, and the insulation layer71: as shown in Table 2

The temperature during simultaneous firing was 800° C., and the firing time was 1 hour.

In the laminates41of Examples 13 to 24, the insulation layer71made of the same material as the outermost layer7was formed so that it surrounded a side surface that was not connected to the first external terminal5of the positive electrode layer1and a side surface that was not connected to the second external terminal6of the negative electrode layer2in a plan view.

Here, in Table 2, (100%) means that the outermost layer7and the insulation layer71were composed of only an insulator obtained by sintering the insulator raw materials. In addition, in Table 2, when two insulator raw materials are listed, this means that the outermost layer7and the insulation layer71were made of an insulator obtained by sintering two insulator raw materials. 50%/50% means that two insulator raw materials were mixed at a ratio of 50%:50%.

In the same manner as in Example 1, the first external terminal5and the second external terminal6were produced on the surfaces at both ends of the laminate41.

Table 2 shows the softening point of the insulator raw materials constituting the outermost layer7and the insulation layer71.

Table 2 shows the coefficient of thermal expansion of the insulator raw materials used for the outermost layer7and the insulation layer71.

In the same manner as in Example 1, performances of the all-solid lithium ion secondary batteries of Examples 13 to 24 were evaluated. The residual voltage after 24 hours is shown in Table 2.

As shown in Table 2, Examples 13 to 24 were the same as Examples 1 to 12 except that the insulation layer71made of the same material as the outermost layer7instead of the material of the solid electrolyte3was formed so that it surrounded aside surface that was not connected to the first external terminal5of the positive electrode layer1and aside surface that was not connected to the second external terminal6of the negative electrode layer2in a plan view.

As shown in Table 2, Examples 13 to 24 had a higher residual voltage after 24 hours than Examples 1 to 12. This is thought to have been caused by the fact that, in Examples 13 to 24, self-discharging was effectively curbed due to formation of the insulation layer71, and a decrease in the residual voltage after 24 hours was minimized.

REFERENCE SIGNS LIST

1Positive electrode layer1A Positive electrode current collector layer1B Positive electrode active material layer2Negative electrode layer2A Negative electrode current collector layer2B Negative electrode active material layer3Solid electrolyte4Laminate5First external terminal6Second external terminal7Outermost layer10All-solid lithium ion secondary battery