JP7068630B2 - All solid state battery - Google Patents

Description

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

In recent years, lithium-ion secondary batteries have been used for small portable power supplies such as personal computers and mobile terminals, large power supplies for equipment such as aircraft, satellites, and factories, electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). ), Etc., have been suitably used as a power source for driving a vehicle. In a lithium ion battery, charge and discharge are performed by moving lithium ions, which are electrolyte ions, between the positive and negative electrodes, and lithium ions are released from the negative electrode active material and stored in the positive electrode active material based on the electrochemical reaction. Current can be taken out to an external circuit.

In the conventional lithium ion battery, a liquid non-aqueous electrolyte solution is mainly used as the electrolyte. While the non-aqueous electrolyte can form a good reaction interface by getting wet with the active material, it is flammable and therefore has a safety problem. Therefore, in recent years, the practical application of all-solid-state batteries using an inorganic solid solid electrolyte has been energetically promoted. In the case of mass production, this all-solid-state battery is manufactured by using a powder material as a battery element. A battery element made of a powder material has a problem of high interfacial resistance, and in order to reduce the interfacial resistance, it is preferable to restrain the battery with a pressure higher than that of a conventional liquid-based secondary battery. In particular, in the above-mentioned all-solid-state battery used as a power source for driving a vehicle, high output characteristics are required, and therefore, application of a higher confining pressure is desired.

Japanese Unexamined Patent Publication No. 2008-103288 Japanese Unexamined Patent Publication No. 2004-103415

By the way, as an exterior material of a secondary battery, an exterior material made of a laminated film that is lightweight and can be miniaturized is widely used. Since the laminated film has a high degree of freedom of deformation, it is also preferable in that the restraining pressure can be transmitted to the battery element with high efficiency. This laminated film is generally composed of a high-strength protective layer, a metal layer for heat resistance, and a heat seal layer for heat welding, which are laminated from the outside. The heat seal layer is generally made of unstretched polypropylene. However, for a battery constrained with a high restraining pressure, since the battery element and the laminated film are in close contact with each other, the heat seal layer is strongly pressed in the laminating direction when the battery element expands due to charging and discharging, and the heat seal is performed. Large tensile stresses can occur in the plane direction of the layer. This tensile stress may damage or break the heat seal layer and even the entire laminated film due to repeated charging and discharging. Breaking of the laminated film is a situation that should be avoided in order to allow the inflow of outside air into the exterior material and increase the possibility of reaction between the battery element and the moisture contained in the outside air during long-term use.

The present invention has been made in view of this point, and an object thereof is an all-solid-state battery capable of suppressing breakage and breakage of a laminated film even when the battery element repeatedly expands and contracts significantly. Is to provide.

The all-solid-state battery disclosed herein includes a battery element in which a positive electrode, a solid electrolyte, and a negative electrode are superposed, an exterior material made of a laminate film accommodating the battery element, and between the battery element and the exterior material. A resin sheet to be arranged and provided. The resin sheet is made of a fluororesin having a compressive strength of 12 MPa or more and 20 MPa or less.
According to such a configuration, even when the all-solid-state battery is constrained by a higher restraining pressure than before, the resin sheet stretches the compressive stress generated by the expansion of the battery element in the plane direction with low friction. By doing so, it can be suitably opened. As a result, damage and breakage of the laminated film can be suppressed. The compressive strength described above can be measured according to the basic test method for the compressive properties of a hard plastic specified in ASTM D695.

In Patent Document 1, a battery element composed of a positive electrode, a negative electrode, and a solid electrolyte is covered and sealed with a thermoplastic resin or a thermosetting resin containing an adsorbent and / or an alkaline substance, and then the outside thereof is further covered. A configuration covered with a moisture-proof laminated film is disclosed. As a result, when a compound containing sulfur is used as the solid electrolyte, even if sulfur reacts with water to generate toxic hydrogen sulfide gas in the battery, the hydrogen sulfide gas can be captured and rendered harmless. Have been described. Further, Patent Document 2 discloses a configuration in which an elastic body that imparts elastic force is arranged in the stacking direction of the battery elements and vacuum-packed with a laminated film. As a result, it is described that even if the battery element is thermally expanded, it is uniformly pressed by the elastic body, and the wavy deformation of the sheet-shaped current collector and the separator can be suppressed. The batteries disclosed in these prior arts are similar to the techniques disclosed herein in that a resin material is present between the battery element and the laminated film. However, these prior arts do not disclose any resin selection and battery configuration that can adequately suppress damage and breakage of the laminated film. In this respect, the techniques disclosed herein may provide an all-solid-state battery that exhibits new effects.

It is a top view which shows typically the structure of the all-solid-state battery which concerns on one Embodiment. FIG. 3 is a cross-sectional view taken along the line AA of FIG. It is sectional drawing explaining the state of the laminated film when the battery element expanded, the case where (A) the conventional resin sheet and (B) the resin sheet disclosed here are used.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. It should be noted that matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention (for example, general configurations and manufacturing processes of all-solid-state batteries that do not characterize the present invention) are described. It can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art. Further, the dimensional relations (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relations. The notation "X to Y" indicating the range means "X or more and Y or less".

FIG. 1 is a plan view schematically showing the structure of an all-solid-state battery (hereinafter, may be simply referred to as “battery” or the like) 10 according to an embodiment. FIG. 2 is a cross-sectional view taken along the line AA of FIG. The all-solid-state battery 10 is a secondary battery that can be repeatedly charged and discharged, and is, for example, a lithium ion battery. Although not specifically shown, the all-solid-state battery 10 disclosed herein includes a positive electrode, a solid electrolyte layer, and a negative electrode, and the positive electrode, the solid electrolyte layer, and the negative electrode are laminated in this order. The battery element 20 is composed of the positive electrode, the solid electrolyte layer, and the negative electrode, and the battery element 20 is housed in an exterior material 40 made of a laminated film and sealed. The all-solid-state battery 10 is provided with a resin sheet 30 between the battery element 20 and the exterior material 40. Hereinafter, each component will be described.

The solid electrolyte layer mainly contains a solid electrolyte material. The solid electrolyte layer may contain a binder (binder), if necessary. For example, when the solid electrolyte material is a powder, the solid electrolyte layer is formed by applying a solid electrolyte paste obtained by kneading a powdery solid electrolyte material and a binder in an appropriate dispersion medium to the surface of the base material. It can be easily produced by drying. The base material referred to here may be a carrier sheet such as a polyethylene terephthalate (PET) film, or may be the surface of the active material layer of the negative electrode and the positive electrode described later.
Further, in the present specification, "mainly" means that the component is contained in an amount of 50% by mass or more unless otherwise specified. It may preferably contain 60% by mass or more, more preferably 70% by mass or more, for example, 80% by mass or more.

The solid electrolyte layer has lithium ion conductivity but does not exhibit electron conductivity. As the solid electrolyte material, for example, various compounds having lithium ion conductivity but not electron conductivity can be preferably used. Specific examples of such a solid electrolyte material include crystalline oxides such as Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO _2.94 , and Li ₇ La ₃ Zr ₂ O ₁₂ . Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O ₃ , 50 Li ₄ SiO 4-50 Li ₃ BO ₃ , Li ₂ O _- B ₂ O _3- (P ₂ O ₅ , ZnO), Li _3.6 Si _0.6 P _0.4 O ₄ , Li _1.07 Al _0.69 Ti _1.46 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ and other amorphous oxides, Li _2.9 PO _3.3 N _0.46 and other amorphous oxynitrides, Li Crystalline nitrides such as 3N, crystalline sulfides such as Li _{10 GeP 2} S ₁₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₂ S-Si S ₂ , Li ₂ SP ₂ S ₅ , Li ₂ S -B ₂ S ₃ , Li ₂ SP ₂ S ₅ -GeS ₂ , Li ₃ PO ₄ -Li ₂ S-SiS ₂ , Li ₃ PO ₄ -Li ₂ S-SiS, Li ₃ PO ₄ -Li ₂ S- Si ₂ S, etc., LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SB ₂ S ₃ , LiI-Li ₂ S, etc., to which lithium halide is added. Amorphous sulfides such as -P ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₃ PS ₄ -LiI-LiBr, and Li ₂ SP ₂ S ₅ -LiI-LiBr, and Examples thereof include iodides such as LiI, LiI-Al ₂ O ₃ , and Li ₃ N-LiI-LiOH. Among them, a sulfide-based solid electrolyte material can be preferably used, and an amorphous sulfide can be particularly preferably used because it has excellent lithium ion conductivity. The amorphous material here includes not only glass but also glass ceramics.

As the solid electrolyte, a semi-solid polymer electrolyte such as polyethylene oxide containing a lithium salt, polypropylene oxide, polyvinylidene fluoride, or polyacrylonitrile can also be used.
The thickness of the solid electrolyte layer is not particularly limited. It is exemplified that the thickness of the solid electrolyte layer is, for example, 20 μm or more and 200 μm or less, typically 100 μm or less, for example, 100 μm or less.

The binder is the same as the binder used for forming the bulk layer of this type of battery (that is, the solid electrolyte layer formed from the powder material, the negative electrode active material layer described later, and the positive electrode active material layer). It can be adopted as appropriate. For example, vinyl resin such as vinyl acetate copolymer, polyvinyl fluoride, vinyl halide resin such as polyvinylidene fluoride (PVdF), ethylene resin such as polytetrafluoroethylene, polytrifluoroethylene, polyethylene, polyethylene oxide (PEO). ) And other polyalkylene oxides, ethyl cellulose and other cellulose resins, acrylic resins, nitrile rubbers, butyl rubbers, polybutadiene rubbers, styrene butadiene rubbers (SBR), polysulfide rubbers, fluororubbers, acrylonitrile butadiene rubbers and other rubbers and other polymer materials. It can be preferably adopted. The proportion of the binder in the bulk layer of this type of battery is not strictly limited. For example, assuming that the layer constituent material is 100% by mass, 10% by mass or less is appropriate, 5% by mass or less is preferable, and 3% by mass or less. Is more preferable.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer fixed to the surface of the negative electrode current collector. As the negative electrode current collector, a metal sheet having good electron conductivity can be preferably used, for example, copper (Cu), nickel (Ni), iron (Fe), and alloys of these with other elements. Metal leaf such as (for example, SUS steel) is suitable. The negative electrode current collector may include a tab 22 for current collection. The negative electrode active material layer mainly contains the negative electrode active material, and further contains a solid electrolyte material. The negative electrode active material layer can further contain, but is not limited to, a binder if necessary, and binds to, for example, a powdery negative electrode active material material and a sulfide-based solid electrolyte material. It can be easily prepared by applying a negative electrode paste obtained by kneading the agent in an appropriate dispersion medium to the surface (typically both sides) of the negative electrode current collector and drying it. The binder and its proportions may be similar to those described in the solid electrolyte layer section above.

The negative electrode active material may be any material that can reversibly occlude and release the charge carrier. Such a negative electrode active material has no clear limitation with the positive electrode active material described later, and the charge / discharge potentials of the two types of active material materials are compared and the charge / discharge potentials show a relatively noble potential. A material having a relatively low potential can be used as a positive electrode active material, and a material having a relatively low potential can be used as a negative electrode active material. Typical examples of such a negative electrode active material include carbon materials such as graphite (graphite), graphitized carbon (hard carbon), easily graphitized carbon (soft carbon), and carbon nanotubes, lithium titanate, and phosphorus. Oxides such as lithium acid metal, vanadium oxide and molybdenum oxide, titanium sulfide, lithium cobalt nitride, lithium silicon oxide, lithium metal (Li), silicon (Si) and tin (Sn) and their oxides (eg, for example). SiO, SnO ₂ ), lithium alloys (eg, LiM ¹ , M ¹ are C, Sn, Si, Al, Ge, Sb, or P), lithium-storable intermetallic compounds (eg, Mg _x M ² and M ³ ). _y Sb, M ² is Sn, Ge, or Sb, M ³ is In, Cu, or Mn), and derivatives and complexes thereof can be mentioned. Further, since the all-solid-state battery disclosed herein can be particularly preferably applied to a battery element having a large volume change due to charge and discharge, graphite-based materials such as natural graphite (stone ink) and artificial graphite, silicon (Si) and Stin (Sn) and compounds thereof can be preferably used. Above all, from the viewpoint of energy density, it is preferable to use a graphite-based material. As the graphite-based material, those in which amorphous carbon is arranged on at least a part of the surface can be further preferably used. More preferably, almost the entire surface of the granular carbon is covered with an amorphous carbon film.

In order to enhance the lithium ion conductivity in the layer of the negative electrode active material layer, in other words, for the purpose of increasing the conduction path of lithium ions, the negative electrode active material layer may preferably contain a solid electrolyte material composed of sulfide. can. The sulfide-based solid electrolyte material made of sulfide may be the solid electrolyte material made of amorphous sulfide or crystalline sulfide described in the above column of solid electrolyte layer. When the solid electrolyte layer is composed of a sulfide-based solid electrolyte material, the negative electrode active material layer preferably contains the same or the same solid electrolyte material as the sulfide-based solid electrolyte material constituting the solid electrolyte layer. The ratio of the solid electrolyte material contained in the negative electrode active material layer can be, for example, 60% by mass or less, preferably 50% by mass or less, when the total of the active material and the solid electrolyte material is 100% by mass. More preferably, it is 40% by mass or less. The proportion of the solid electrolyte material is preferably 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more. A reaction layer having high resistance may be formed at the interface between the negative electrode active material and the solid electrolyte, and the interface resistance may increase. Therefore, in order to suppress such an event, the particles constituting the negative electrode active material may be coated with a crystalline oxide having lithium ion conductivity.

The thickness of the negative electrode active material layer is not particularly limited. In an all-solid-state battery for which a large current is instantly supplied, the thickness of the negative electrode active material layer is preferably thick as long as the electric resistance does not become too high. For example, the thickness of the negative electrode active material layer can be, for example, 50 μm or more and 300 μm or less, typically 200 μm or less, for example 100 μm or less.

The positive electrode includes a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. As the positive electrode current collector, a metal sheet having good conductivity can be preferably used, and for example, a metal foil such as aluminum or an iron alloy (for example, various SUS steels) is suitable. The positive electrode current collector may include a tab 22 for current collection. The positive electrode active material layer mainly contains the positive electrode active material, and may further contain a solid electrolyte material. The positive electrode active material layer can further contain, but is not limited to, a binder, for example, a powdery positive electrode active material material and a solid electrolyte material and a binder. A positive electrode paste prepared by kneading in an appropriate dispersion medium can be easily prepared by applying it to the surface (typically both sides) of the positive electrode current collector and drying it. The binder and its proportions may be similar to those described in the solid electrolyte layer section above.

The positive electrode active material may be any material that can reversibly occlude and release the charge carrier. Suitable examples of the positive electrode active material of the all-solid-state lithium secondary battery include lithium nickel-containing composite oxide, lithium cobalt-containing composite oxide, lithium nickel cobalt-containing composite oxide, lithium manganese-containing composite oxide, and lithium nickel cobalt manganese-containing. Examples thereof include lithium transition metal composite oxides such as composite oxides. From the viewpoint of high durability, a so-called 4V class positive electrode active material such as a layered lithium nickel cobalt manganese-containing composite oxide having an operating potential of 4.2V or less based on metallic lithium is preferable. From the viewpoint of achieving high output at one time, a so-called 5V class positive electrode such as lithium nickel manganese oxide having a spinel structure having an operating potential exceeding 4.2V and about 5.2V or less based on metallic lithium is used. Active material is preferred.

In order to enhance the lithium ion conductivity in the positive electrode active material layer, the positive electrode active material layer can preferably contain a solid electrolyte material as described above. In this case, the solid electrolyte material contained in the positive electrode active material layer is preferably the same or the same material as the solid electrolyte material constituting the solid electrolyte layer. The ratio of the solid electrolyte material contained in the positive electrode active material layer can be, for example, 60% by mass or less, preferably 50% by mass or less, when the total of the active material and the solid electrolyte material is 100% by mass. More preferably, it is 40% by mass or less. The proportion of the solid electrolyte material is preferably 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more. A reaction layer having high resistance may be formed at the interface between the positive electrode active material and the solid electrolyte, and the interface resistance may increase. Therefore, in order to suppress such an event, the particles constituting the positive electrode active material may be coated with a crystalline oxide having lithium ion conductivity.

The thickness of the positive electrode active material layer is not particularly limited. In an all-solid-state battery for which a large current is instantly supplied, the thickness of the negative electrode active material layer is preferably thick as long as the electric resistance does not become too high. For example, the thickness of the positive electrode active material layer can be, for example, 50 μm or more and 300 μm or less, typically 200 μm or less, for example 100 μm or less.

In the above positive electrode, negative electrode and solid electrolyte layer, the positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode are superposed on each other so as to be insulated by the solid electrolyte layer to form the battery element 20. The direction in which each layer is superposed is hereinafter referred to as "stacking direction". In the configuration of FIG. 1, the orientation of the stacking of the positive electrode and the negative electrode is adjusted so that the tabs 22 of the positive electrode and the negative electrode for current collection are arranged apart from each other on one side of the exterior material 40. One battery element 20 may be provided with only one laminated unit of the positive electrode, the solid electrolyte layer, and the negative electrode, or may be provided by stacking two or more (for example, three to six). .. The battery element 20 is sealed by a laminating film as an exterior material 40.

By accommodating and sealing the battery element 20 in the exterior material 40, it is possible to suppress decomposition / deterioration of the battery element, particularly the solid electrolyte material, due to unintended content of water or oxidation. The exterior material 40 is not particularly limited in its outer shape, material, and the like as long as it is made of a laminated film that can be used as an exterior material for this type of secondary battery. By using the laminated film exterior material 40, unlike a metal can, the battery can be made thinner and lighter. Further, since the laminating film exterior material 40 has a high degree of freedom in shape, the confining pressure can be transmitted to the battery element with high efficiency, for example, when the battery is constrained with a high confining pressure. The laminated film is generally composed of a foil-like metal and a resin sheet laminated together. As an example, typically, an aluminum foil or an aluminum vapor-deposited layer and a polyethylene terephthalate are used for the purpose of imparting heat resistance, sealing strength, impact resistance, etc. to the surface of a non-stretched (CPP) polypropylene film for heat welding. A laminated film having a three-layer structure in which a film made of lidatate (PET) or nylon is laminated can be preferably used. The exterior material 40 made of a laminated film may be, for example, previously molded into a bag shape, or may be of a type in which a battery element 20 is arranged between two laminated films and welded over the entire circumference. May be good.

In the all-solid-state battery 10 disclosed here, the resin sheet 30 is interposed between the battery element 20 and the exterior material 40. The resin sheet 30 is characterized by being composed of a fluororesin having a compressive strength of 12 MPa or more and 20 MPa or less. The fluororesin is an organic polymer fluorine compound in which at least a part of the ends of the main chain and the side chain of the carbon skeleton is terminated with fluorine (F). Fluororesin is generally characterized by being excellent in heat resistance, chemical resistance, electrical characteristics (high frequency characteristics), non-adhesiveness, self-lubricating property, etc., as compared with other resins. Further, a fluororesin having a compressive strength of 20 MPa or less in the thickness direction has a feature that it is more easily deformed by compressive stress than, for example, other resins. The compressive strength of the fluororesin is more preferably 18 MPa or less, more preferably 16 MPa or less, and particularly preferably 14 MPa or less. However, the compressive strength is preferably 12 MPa or more in order to have a strength that does not break due to compression by the battery element 20. Based on these characteristics, the resin sheet 30 can alleviate the compressive stress in the stacking direction generated by the expansion of the battery element by charging and discharging by deforming the sheet itself. Further, when the resin sheet 30 is stretched in the plane direction due to the compressive stress in the laminating direction, it is possible to suppress the tensile stress converted from the compression direction to the plane direction from propagating to the exterior material 40 due to its low coefficient of friction. can.

That is, for example, as shown in FIG. 3A, when a resin sheet other than the above-mentioned fluororesin is arranged between the battery element 20 and the exterior material 40 as the resin sheet 30, between the resin sheet 30 and the exterior material 40. Since a relatively large amount of friction is generated in the resin sheet 30, tensile stress is also generated in the surface direction of the exterior material 40 corresponding to the stretching of the resin sheet 30 in the surface direction. On the other hand, as shown in FIG. 3B, when the above-mentioned fluororesin sheet is arranged as the resin sheet 30 between the battery element 20 and the exterior material 40, it is between the resin sheet 30 and the exterior material 40. The friction of the resin sheet 30 is remarkably reduced, and the resin sheet 30 slips on the surface of the exterior material 40 when stretched in the surface direction, and suppresses the generation of tensile stress in the surface direction of the exterior material 40. Such an action effect can be exhibited particularly effectively when the all-solid-state battery 10 for vehicle drive use is constrained to a fixed size with an unprecedented high restraint pressure.

Examples of the fluororesin constituting such a resin sheet 30 include polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene / hexafluoro. Examples thereof include high molecular weight fluoropolymers typified by propylene copolymer (FEP) and the like. In the fluororesin, the degree of polymerization, the ratio of specific monomer units in the copolymer, the number of carbon atoms in the side chain, and the like are not particularly limited as long as the above compressive strength is satisfied. These fluororesins can have a compressive strength of 12 MPa or more and 20 MPa or less. In addition, these fluororesins contain fluorine atoms in all or most of the ends of the main chain and side chains of the carbon skeleton. Therefore, since it contains almost no hydrocarbon unit (-CH _2- ), the compressive strength is slightly lower as described above, and the friction coefficient is dramatically reduced.

For example, the friction coefficient of these fluororesins is typically PTFE (0.08 to 0.12 / 0.03 to 0.08) as (static friction coefficient / dynamic friction coefficient), and PFA (0.08). ~ 0.12 / 0.04 ~ 0.08), FEP (0.10 ~ 0.14 / 0.05 ~ 0.10), which are extremely small. The coefficient of friction of these fluororesins is approximately 0.15 or less in terms of static friction coefficient and 0.1 or less in terms of dynamic friction coefficient.
Even if the same fluororesin is used, in polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene / ethylene copolymer (ETFE), chlorotrifluoroethylene / ethylene copolymer (ECTFE), etc., the main chain / It has many hydrocarbon units (-CH _2- ) as well as fluorocarbon units (-CF _2- ) in the side chain. Therefore, the compressive strength is as high as about 30 MPa or more, and the friction coefficient is dramatically higher than that of the above-mentioned fluororesin, although it is lower than that of other non-fluorinated resins. For reference, as an example, the coefficient of friction (static friction coefficient / dynamic friction coefficient) is ETFE (0.23 to 0.29 / 0.21 to 0.23) and ETFE (0.23 to 0.29 / 0.21). ~ 0.23), ETFE (0.38 ~ 0.42 / 0.34 ~ 0.38).

The thickness of the resin sheet 30 is not particularly limited. Considering the effect of relaxing the compressive strength of the resin sheet 30, the resin sheet 30 is preferably as thick as possible, and considering the increase in battery bulk, the resin sheet 30 is preferably as thin as possible. For example, the balance between the two is optimized. can. For example, the thickness of the resin sheet 30 (which is the average thickness; the same applies hereinafter) can be 50 μm or more, 300 μm or less, typically 200 μm or less, for example, 100 μm or less. The resin sheet 30 is arranged so that when the battery element 20 is compressed in the stacking direction and expanded by charging / discharging, it is deformed together with the battery element 20 to prevent direct contact between the battery element 20 and the exterior material 40. It should be done. For example, the resin sheet 30 is two sheets having the same size and shape as the outer shape of the battery element 20 when viewed from the stacking direction, and the battery element 20 and the battery element 20 are sandwiched from both ends in the stacking direction. It may be arranged between the exterior material 40 and the exterior material 40. On the other hand, the solid electrolyte layer also serves as a separator and an electrolytic solution in the liquid-based secondary battery. However, unlike the separator, the solid electrolyte layer does not have a continuous phase in the plane direction, and therefore has no strength. From this point of view, the resin sheet 30 may be long and may be arranged between the battery element 20 and the exterior material 40 in a state where the entire battery element 20 is wound.

Further, when the all-solid-state battery 10 is a bulk type all-solid-state battery in which each of the above layers is made of a powder material, the purpose is to reduce the interfacial resistance between the particles constituting the powder material, and the high energy density. In some cases, compressive stress is applied in the stacking direction of each layer (direction orthogonal to the current collector) for the purpose of realizing the above. This compressive stress can be suitably applied, for example, by using a restraining mechanism (not shown). From this point of view, the all-solid-state battery 10 disclosed herein may include a restraining mechanism including a pair of end plates and a restraining member. The end plate is a plate-shaped member arranged at both ends of the all-solid-state battery 10 in the stacking direction so as to sandwich one or more all-solid-state batteries 10 in the stacking direction of the battery elements 20. The restraining member is a rod-shaped member (for example, a substantially U-shaped member in cross-sectional view) that is passed over the pair of end plates in order to keep the distance between the pair of end plates constant. The restraining member sandwiches the all-solid-state battery 10 in the stacking direction by the end plates, reduces (compresses) the distance between the end plates so that a predetermined restraining pressure is generated in the stacking direction, and then keeps the distance between the end plates constant. To maintain, it is passed over and fixed to a pair of end plates. The end plate and the restraining member may be fixed by a fixing member such as a bolt or a nut. As the restraining member, a plurality of restraining members may be arranged on the outer periphery of the end plate in a well-balanced manner so that the compressive stress applied to the all-solid-state battery 10 becomes uniform. The end plate and the restraining member are made of a material having mechanical strength that is not deformed by the restraining pressure and the compressive stress generated when the battery element 20 expands and contracts (for example, stainless steel metal, fiber reinforced plastic, etc.). It is composed of composite materials, etc.).

The restraining pressure applied to the all-solid-state battery 10 may be, for example, about 0.1 MPa or more, preferably 1 MPa or more, more preferably 2 MPa or more, particularly preferably 5 MPa or more, and for example, 10 MPa or more. The upper limit of the compressive stress is not particularly limited, and for example, it can be appropriately set according to the maximum stress that can be applied to the all-solid-state battery 10 by the compressive stress application device or the like to be used. Such an average restraining pressure can be, for example, about 50 MPa or less, for example, 20 MPa or less. Such a high compressive stress can be about 5 to 10 times or more the compressive stress of a liquid-based secondary battery using a non-aqueous electrolytic solution.

According to the above configuration, a resin sheet 30 made of a fluororesin having a predetermined configuration is arranged between the battery element 20 of the all-solid-state battery 10 disclosed herein and the exterior material 40 made of a laminated film. Further, the resin sheet 30 is made of a fluororesin having a compressive strength of 12 MPa or more and 20 MPa or less. As a result, even when the battery element 20 repeatedly expands and contracts due to charging and discharging, damage or breakage of the exterior material 40 due to the battery element 20 can be suppressed. In particular, even when a high restraining pressure is applied in the stacking direction of the all-solid-state battery 10, the compressive stress due to the battery element 20 is relaxed by the compressive deformation of the resin sheet 30, and the slip characteristics of the resin sheet 30 are relaxed. Therefore, the transmission to the exterior material 40 can be suppressed and opened. This means that the same effect can be exhibited even when the battery element 20 greatly expands and contracts due to high-rate charging / discharging in which the all-solid-state battery 10 instantly charges or discharges a large current.

In the above embodiment, the laminating film constituting the exterior material 40 has a three-layer laminated structure made of CPP / Al / nylon. However, the number of layers and the material of the laminated film are not limited to this. For example, in the laminated film, instead of CPP, a polyolefin resin such as polyethylene (PE) that can be heat-fused, ethylene vinyl acetate (EVA), various ionomer resins, and other resins are used as the heat seal layer. Can be done. As the metal layer, for example, nickel (Ni), stainless steel, copper (Cu), titanium (Ti), iron (Fe), or the like can be adopted instead of aluminum. As the protective layer, instead of nylon, PTFE, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyphenylene ether (PPE), modified products thereof and the like can be used. Further, the laminating film may have a two-layer structure of a heat seal layer and a metal layer, or may be additionally provided with another layer. However, according to the technique disclosed herein, it is not necessary to particularly increase the strength of the laminated film constituting the exterior material 40, and damage or breakage thereof can be suppressed.

Since the cause of the breakage of the laminated film, which is the exterior material 40, is remarkably seen by the expansion and contraction of the battery element 20, the above effect may be due to the large and / or steep expansion and contraction of the battery element 20. It is easy to find in the all-solid-state battery 10 of the application. In addition, the safety associated with the electrolyte-less structure of the all-solid-state battery 10 is particularly required for all-solid-state batteries in applications that are expected to be used by general consumers for a long period of time. Therefore, the non-aqueous electrolyte secondary battery disclosed herein can be particularly preferably used as a main battery for driving a motor mounted on a vehicle such as a plug-in hybrid vehicle, a hybrid vehicle, or an electric vehicle. can.

Hereinafter, examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Manufacturing of lithium-ion secondary battery for evaluation>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (LNMC) whose particle size has been adjusted to 1 to 10 μm as a positive electrode active material, sulfide solid electrolyte powder as a solid electrolyte, and acetylene black as a conductive auxiliary material. Using (AB) and PVdF as a binder, the active material: solid electrolyte = 75:25 (mass ratio), 2 parts by mass of the conductive auxiliary material and 1.5 parts by mass of the binder with respect to 100 parts by mass of the active material. Weighed in proportion and these materials were dispersed in butyric acid using an ultrasonic homogenizer (UH-50, manufactured by SMT) to prepare a positive electrode paste having a solid content of 50% by mass. This paste was applied to both sides of a tabbed aluminum foil as a positive electrode current collector and dried to form a positive electrode active material layer, which was used as a positive electrode.

Natural graphite (C) as a negative electrode active material powder, sulfide solid electrolyte powder as a solid electrolyte, and styrene butadiene rubber (SBR) as a binder are used as an active material: solid electrolyte = 60:40 (mass ratio). Weighed at a ratio of 1.1 parts by mass of the binder to 100 parts by mass of the active material, and kneaded these materials with butyric acid as a dispersion medium using an ultrasonic homogenizer (UH-50, manufactured by SMT) to obtain a negative electrode. A paste was prepared. This paste was applied to both sides of a tabbed copper foil as a negative electrode current collector and dried to form a negative electrode active material layer, which was used as a negative electrode.

A sulfide solid electrolyte powder as a solid electrolyte and PVdF as a binder are used in a mass ratio of solid electrolyte: binder = 95: 5, and dispersed in heptane using an ultrasonic homogenizer (UH-50, manufactured by SMT). A solid electrolyte paste having a solid content of 50% by mass was prepared. This paste was applied to the surface of one of the plurality of positive electrode and negative electrode active material layers prepared above and dried to form a solid electrolyte layer.
Then, the prepared positive electrodes and negative electrodes with the solid electrolyte layer are stacked so that the active material layers of each electrode are insulated by the solid electrolyte layer and the tabs for collecting electricity are arranged at the same positions for each electrode. So, I used it as a battery element.

The prepared battery elements were sandwiched between two laminated films via the polymer sheet shown in Table 1 below, and the entire peripheral edge was heat-welded to prepare the all-solid-state batteries of Examples 1 to 7. All polymer sheets used had a thickness of 0.1 mm. Further, the laminated film includes a surface layer made of nylon, an aluminum vapor-deposited layer, and a heat-sealing layer made of polypropylene, and is heated by stacking and heating two laminated films so that the heat-sealing layers face each other. The parts are heat-welded to each other and joined together. The all-solid-state battery prepared in this way is set so that the restraining pressure is 10 MPa by using a restraining jig consisting of two SUS steel end plates (restraint plates) and restraint members (bolts and nuts). I restrained myself.

Then, the all-solid-state batteries of Examples 1 to 7 in the restrained state were placed in a constant temperature bath at 80 ° C., and a cycle test was conducted in which charging and discharging were performed 1000 times in a battery voltage range of 3V to 4V with a current of 1C. The temperature of 80 ° C. deteriorates the battery characteristics and induces softening of the heat seal layer of the polymer sheet and the laminated film, and promotes the breakage of the heat seal layer of the laminated film triggered by expansion and contraction of the battery element. It is a condition to generate in. Then, the battery after the cycle test was disassembled, and the surface of the laminated film facing the battery element was observed to confirm the presence or absence of damage such as tearing and cutting. The results are shown in Table 1.

For reference, the compressive strength and the coefficient of dynamic friction of the polymer sheets of each example are also shown in Table 1. The compressive strength is a result measured according to the basic test method for the compressive properties of a hard plastic specified in ASTM D695. The dynamic friction coefficient is a value disclosed in RC Bowers, Journal of Applied Physics 42, 4961 (1971), and the FEP is a value slightly different from the above-mentioned example.

[evaluation]
As shown in Example 4 of Table 1, when nothing was interposed between the battery element and the laminated film, it was confirmed that the inner surface of the laminated film was damaged after 1000 times of charging and discharging. rice field. It was confirmed that not only the heat-sealed layer but also the aluminum-deposited layer had tears at the positions facing the corners of the battery element of the laminated film.

On the other hand, when the polymer sheets of Examples 1 to 3 were inserted between the battery element and the laminated film, it was confirmed that there was no damage such as tearing in the sheet resin portion of the laminated film. On the other hand, when the polymer sheets of Examples 5 and 6 were inserted, it was confirmed that the heat seal layer of the laminated sheet was damaged after the cycle test. It was also confirmed that the heat seal layer of the laminated sheet was damaged after the cycle test when the polymer sheet of Example 7 which was a fluororesin was inserted.

The above results show that the fluoropolymer sheets (PTFE, FEP, PFA) having a compressive strength of 20 MPa or less in Examples 1 to 3 are interposed between the battery element and the laminated film, so that the battery is charged and discharged. It is considered that this is because the polymer sheet was preferentially compressed by the expansion and contraction of the element, and the heat seal layer of the laminated film could be suitably suppressed from compressive deformation (tensile deformation in the plane direction). In addition, since the fluororesin-based polymer sheet has a low coefficient of friction, a configuration is constructed in which the tensile elongation deformation that occurs in the plane direction when compressionally deformed can be dissipated without being transmitted to the heat seal layer of the adjacent laminated film. It is probable that it was done.

However, in the polymer sheet made of polyvinylidene chloride of Example 5 and polyethylene of Example 6, which have the same compressive strength as the polymer sheets of Examples 1 to 3, even if the sheet itself is compressed, it is compressed in the plane direction. It is probable that the generated elongation deformation was directly transmitted to the laminating film and damaged the laminating film.
Further, even if the polymer sheet is made of fluororesin, in the polymer sheet of Example 7 made of ETFE having high compression strength, the polymer sheet is not compressed when the battery element expands and contracts, and the laminated film is greatly deformed. Therefore, it is considered that the heat seal layer of the laminated film is damaged.

From the above, according to the all-solid-state battery according to the present embodiment, even when the battery element repeatedly expands and contracts with the resin interposed between the battery element and the laminated film, it is covered with the resin. It is possible to suppress breakage and breakage of the laminated film. Further, it was confirmed that such an effect can be sufficiently obtained even with an all-solid-state battery for which a large current is repeatedly charged and discharged while being restrained by a high restraining load.
Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

10 All-solid-state battery 20 Battery element 30 Resin sheet 40 Exterior material

Claims (1)

A battery element on which a positive electrode, a solid electrolyte and a negative electrode are superimposed,
An exterior material made of a laminated film that houses the battery element, and
A resin sheet arranged between the battery element and the exterior material,
Equipped with
The resin sheet is an all-solid-state battery having a compressive strength of 12 MPa or more and 20 MPa or less and made of a fluororesin.

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