JP7453765B2 - All solid state battery - Google Patents

Description

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

In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. In the automobile industry, expectations are high for reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and non-aqueous batteries such as secondary batteries for motor drives hold the key to their practical application. Electrolyte secondary batteries are actively being developed.

Secondary batteries for motor drives are required to have extremely high output characteristics and high energy compared to consumer lithium ion secondary batteries used in mobile phones, notebook computers, and the like. Therefore, lithium ion secondary batteries, which have the highest theoretical energy of all practical batteries, are attracting attention and are currently being rapidly developed.

The currently widely used lithium-ion secondary batteries use a flammable organic electrolyte as the electrolyte. These liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, overcharging, etc. than other batteries.

Therefore, in recent years, research and development on all-solid-state lithium ion secondary batteries using oxide-based or sulfide-based solid electrolytes as electrolytes has been actively conducted. A solid electrolyte is a material mainly composed of an ion conductor capable of ion conduction in a solid state. Therefore, in principle, all-solid-state lithium ion secondary batteries do not suffer from various problems caused by flammable organic electrolytes, unlike conventional liquid-based lithium ion secondary batteries. Furthermore, in general, the use of high-potential, large-capacity positive electrode materials and large-capacity negative electrode materials can significantly improve the output density and energy density of the battery.

Incidentally, the volume of the electrode active material changes as it is charged and discharged. In an all-solid-state lithium ion secondary battery, the electrode active material layer contains an electrolyte in addition to the electrode active material, but this electrolyte is solid and does not easily follow changes in the volume of the electrode active material. Therefore, the electrode structure changes (separation between the electrode active material and the solid electrolyte) during charging and discharging, which may lead to an increase in internal resistance. As a technique for preventing peeling between an electrode active material and a solid electrolyte, for example, Patent Document 1 discloses an all-solid-state technology having an electrode layer containing an active material, a sulfide solid electrolyte, and a hydrogenated rubber material that binds these together. A lithium ion secondary battery is disclosed.

Japanese Patent Application Publication No. 2011-134675

However, according to studies by the present inventors, it has been found that when the technique described in Patent Document 1 is used, the use of a binder that does not contribute to the reaction causes a decrease in energy density.

Therefore, an object of the present invention is to provide a means for suppressing an increase in internal resistance while suppressing a decrease in energy density in an all-solid-state battery.

The present inventors conducted extensive studies to solve the above problems. As a result, it is possible to control the amount of volume change of the electrode active material layer and the amount of volume change of the solid electrolyte due to charging and discharging so that they satisfy a predetermined relationship, or the amount of volume change of the electrode active material layer and the solid electrolyte due to charging and discharging. The present inventors have discovered that it is effective to control the volume change amount of the layer so that it satisfies a predetermined relationship, and have completed the present invention.

That is, an all-solid-state battery according to one embodiment (first embodiment) of the present invention includes a power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and the power generation element. A restraining member is provided for restraining in the stacking direction. At least one of the positive electrode and the negative electrode has an electrode active material layer containing an electrode active material and a solid electrolyte disposed on the surface of a current collector, and in the electrode active material layer, the electrode The method is characterized in that the ratio of the amount of change in volume of the solid electrolyte to the amount of change in volume of the active material is 1 or more.

An all-solid-state battery according to another embodiment (second embodiment) of the present invention includes a power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and a stack of the power generation elements. A restraining member is provided for restraining in the direction. The battery is characterized in that the ratio of the volume change of the solid electrolyte layer to the volume change of the electrode active material layers constituting the positive electrode and the negative electrode during charging and discharging is 1 or more.

According to the all-solid-state battery according to one embodiment of the present invention, it is possible to suppress an increase in internal resistance while suppressing a decrease in energy density.

1 is a cross-sectional view schematically showing a stacked type (internal parallel connection type) all-solid-state lithium ion secondary battery that is an embodiment of the present invention. 1 is a cross-sectional view schematically showing a bipolar all-solid-state lithium ion secondary battery that is an embodiment of the present invention. 1 is a perspective view schematically showing a stacked type (internal parallel connection type) all-solid-state lithium ion secondary battery that is an embodiment of the present invention. 4 is a side view seen from direction A shown in FIG. 3. FIG. 1 is a perspective view showing the appearance of a stacked all-solid-state lithium ion secondary battery that is an embodiment of the present invention. 1 is a graph showing discharge characteristics of all-solid-state lithium ion secondary batteries according to Examples and Comparative Examples.

One form (first form) of the present invention provides a power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and a restraining member that restrains the power generation element in a stacking direction. The present invention relates to an all-solid-state battery comprising: At least one of the positive electrode and the negative electrode has an electrode active material layer containing an electrode active material and a solid electrolyte disposed on the surface of a current collector, and in the electrode active material layer, the electrode The method is characterized in that the ratio of the amount of change in volume of the solid electrolyte to the amount of change in volume of the active material is 1 or more. According to the all-solid-state battery of this embodiment, it is possible to suppress an increase in internal resistance while suppressing a decrease in energy density.

Another form (second form) of the present invention provides a power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and a restraint that restrains the power generation element in a stacking direction. The present invention relates to an all-solid-state battery including the member. The battery is characterized in that the ratio of the volume change of the solid electrolyte layer to the volume change of the electrode active material layers constituting the positive electrode and the negative electrode during charging and discharging is 1 or more. According to the all-solid-state battery of this embodiment, it is possible to suppress an increase in internal resistance while suppressing a decrease in energy density.

The present embodiment will be described below with reference to the drawings, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

FIG. 1 schematically shows the overall structure of a stacked (internal parallel connection type) all-solid-state lithium ion secondary battery (hereinafter also simply referred to as a "stacked secondary battery"), which is an embodiment of the present invention. FIG. The stacked secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which a charge/discharge reaction actually proceeds is sealed inside a laminate film 29 that is a battery exterior body. Note that in the stacked secondary battery 10a, a restraining pressure is applied in the stacking direction of the power generation elements 21 by a restraining member (not shown). Therefore, the volume of the power generation element 21 is kept constant.

As shown in FIG. 1, the power generation element 21 of the stacked secondary battery 10a of this embodiment includes a positive electrode in which positive electrode active material layers 13 are arranged on both sides of a positive electrode current collector 11', a solid electrolyte layer 17, and a negative electrode. It has a structure in which a negative electrode with negative electrode active material layers 15 arranged on both sides of a current collector 11'' is laminated. Specifically, one positive electrode active material layer 13 and the adjacent negative electrode active material layer 15 face each other with the solid electrolyte layer 17 in between, and the positive electrode, the solid electrolyte layer, and the negative electrode are stacked in this order. ing. Thereby, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one single cell layer 19. Therefore, it can be said that the stacked secondary battery 10a shown in FIG. 1 has a configuration in which a plurality of cell layers 19 are stacked and electrically connected in parallel. Note that the positive electrode active material layer 13 is disposed on only one side of the outermost positive electrode current collectors located on both outermost layers of the power generation element 21, but active material layers may be provided on both sides. . That is, instead of using a current collector exclusively for the outermost layer with an active material layer provided on only one side, a current collector with active material layers on both sides may be used as it is as the outermost layer current collector. In addition, by reversing the arrangement of the positive electrode and negative electrode from FIG. 1, the outermost layer negative electrode current collector is located on both outermost layers of the power generation element 21, and A negative electrode active material layer may be arranged on both sides.

A positive electrode current collector plate 25 and a negative electrode current collector plate 27 that are electrically connected to each electrode (positive electrode and negative electrode) are attached to the positive electrode current collector 11′ and the negative electrode current collector 11″, respectively. It has a structure in which it is led out to the outside of the laminate film 29 so as to be sandwiched between the two. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are connected to the positive electrode current collector 11' and the negative electrode current collector 11' of each electrode via a positive electrode terminal lead and a negative electrode terminal lead (not shown), respectively, as necessary. ' may be attached by ultrasonic welding, resistance welding, etc.

In the above description, an embodiment of an all-solid-state battery according to one aspect of the present invention has been described using a stacked (internal parallel connection type) all-solid-state lithium ion secondary battery as an example. However, the types of all-solid-state batteries to which the present invention is applicable are not particularly limited, and include a positive electrode active material layer electrically bonded to one surface of the current collector and an electrically bonded layer to the opposite surface of the current collector. It is also applicable to a bipolar type all-solid-state battery including a bipolar type electrode having a bonded negative electrode active material layer.

FIG. 2 is a cross-sectional view schematically showing a bipolar all-solid-state lithium ion secondary battery (hereinafter also simply referred to as a "bipolar secondary battery") according to an embodiment of the present invention. . The bipolar secondary battery 10b shown in FIG. 2 has a structure in which a substantially rectangular power generation element 21, in which a charging/discharging reaction actually proceeds, is sealed inside a laminate film 29, which is a battery exterior body.

As shown in FIG. 2, the power generation element 21 of the bipolar secondary battery 10b of this embodiment has a positive electrode active material layer 13 electrically coupled to one surface of the current collector 11. It has a plurality of bipolar electrodes 23 each having an electrically coupled negative electrode active material layer 15 formed on its opposite surface. In addition, in the bipolar secondary battery 10b shown in FIG. 2, the bipolar electrode 23 is composed of the all-solid-state battery electrode according to this embodiment. Each bipolar electrode 23 is stacked with the solid electrolyte layer 17 in between to form the power generation element 21 . Note that the solid electrolyte layer 17 has a structure in which a solid electrolyte is formed into layers. At this time, the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23 are arranged to face each other with the solid electrolyte layer 17 in between. , bipolar electrodes 23 and solid electrolyte layers 17 are alternately stacked. That is, the solid electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23. has been done.

Adjacent positive electrode active material layer 13 , solid electrolyte layer 17 , and negative electrode active material layer 15 constitute one cell layer 19 . Therefore, it can be said that the bipolar secondary battery 10b has a structure in which the single cell layers 19 are stacked. Note that the positive electrode active material layer 13 is formed only on one side of the outermost layer current collector 11a on the positive electrode side located at the outermost layer of the power generation element 21. Further, the negative electrode active material layer 15 is formed only on one side of the negative electrode side outermost layer current collector 11b located at the outermost layer of the power generation element 21.

Furthermore, in the bipolar secondary battery 10b shown in FIG. 2, a positive electrode current collector plate (positive electrode tab) 25 is arranged adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior body. It is derived from the laminate film 29. On the other hand, a negative electrode current collector plate (negative electrode tab) 27 is arranged adjacent to the outermost layer current collector 11b on the negative electrode side, and is similarly extended and led out from the laminate film 29.

Note that the number of times the cell layer 19 is stacked is adjusted depending on the desired voltage. Furthermore, in the bipolar secondary battery 10b, the number of times the unit cell layers 19 are stacked may be reduced if sufficient output can be ensured even if the thickness of the battery is made as thin as possible. In the bipolar secondary battery 10b, in order to prevent external shocks and environmental deterioration during use, the power generating element 21 is sealed under reduced pressure in a laminate film 29, which is the battery exterior, and the positive electrode current collector plate 25 and the negative electrode collector It is preferable to have a structure in which the electric plate 27 is taken out from the laminate film 29.

FIG. 3 is a perspective view of a stacked secondary battery according to an embodiment of the present invention. FIG. 4 is a side view seen from direction A shown in FIG. 3.

As shown in FIG. 3, the stacked secondary battery 10a according to the present embodiment includes a power generation element 21 sealed in the laminate film 29 shown in FIG. It has two metal plates 200, and a bolt 300 and a nut 400 as fastening members. This fastening member (bolt 300 and nut 400) has the function of fixing the metal plate 200 in a state in which the power generating element 21 sealed in the laminate film 29 is sandwiched therebetween. Thereby, the metal plate 200 and the fastening member (the bolt 300 and the nut 400) function as a restraining member that restrains (pressurizes) the power generation element 21 in the stacking direction thereof. Note that the restraining member is not particularly limited as long as it is a member that can restrain the power generation elements 21 in the stacking direction. Typically, a combination of a plate made of a rigid material such as the metal plate 200 and the above-mentioned fastening member is used as the restraining member. Further, as for the fastening member, not only the bolt 300 and the nut 400 but also a tension plate or the like that fixes the end of the metal plate 200 so as to restrain the power generation element 21 in the stacking direction thereof may be used.

Note that the lower limit of the load (constraining pressure in the stacking direction of the power generation elements) applied to the power generation element 21 is, for example, 0.1 MPa or more, preferably 1 MPa or more, and more preferably 5 MPa or more. The upper limit of the confining pressure in the stacking direction of the power generation elements is, for example, 100 MPa or less, preferably 90 MPa or less, and more preferably 80 MPa or less.

The main components of the above-described stacked secondary battery 10a will be explained below.

[Current collector]
The current collector has a function of mediating the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. There is no particular limitation on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a cladding material of nickel and aluminum, a cladding material of copper and aluminum, etc. may be used. Alternatively, it may be a foil whose metal surface is coated with aluminum. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material to the current collector by sputtering, and the like.

Furthermore, examples of the latter resin having electrical conductivity include resins in which a conductive filler is added to a non-conductive polymer material as necessary.

Examples of non-conductive polymer materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide. (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials can have excellent potential or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material as necessary. In particular, when the resin serving as the base material of the current collector consists only of non-conductive polymers, a conductive filler is inevitably required to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a substance that has conductivity. For example, metals, conductive carbon, and the like are examples of materials with excellent conductivity, potential resistance, or lithium ion blocking properties. The metal is not particularly limited, but includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or containing these metals. Preferably, it contains an alloy or a metal oxide. Furthermore, there are no particular limitations on the conductive carbon. Preferably, it is selected from the group consisting of acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjenblack (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one kind.

The amount of conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally 5 to 80% by mass based on 100% by mass of the total mass of the current collector. It is.

Note that the current collector may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include at least a conductive resin layer made of a resin having conductivity. Further, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided on a part of the current collector.

[Electrode active material layer]
At least one of the positive electrode and the negative electrode according to this embodiment has an electrode active material layer containing an electrode active material and a solid electrolyte disposed on the surface of the current collector.

In the first embodiment of the present invention, the electrode active material layer (positive electrode active material layer/negative electrode active material layer) includes an electrode active material (positive electrode active material/negative electrode active material) and a solid electrolyte. In this specification, unless otherwise specified, items common to the positive electrode and the negative electrode will be referred to as "electrode."

The first aspect of the present invention is characterized in that, in the electrode active material layer, the ratio of the volume change of the solid electrolyte to the volume change of the electrode active material accompanying charging and discharging is 1 or more. In this specification, the ratio of the volume change of the solid electrolyte to the volume change of the electrode active material due to charging and discharging is also referred to as "solid electrolyte/electrode active material ratio."

By controlling the ratio of solid electrolyte/electrode active material to 1 or more, the solid electrolyte can be elastically deformed (increase in volume) in response to changes in the volume of the electrode active material during charging and discharging, especially when the volume of the electrode active material decreases. Accordingly, separation between the electrode active material and the solid electrolyte can be suppressed. Therefore, it is possible to suppress an increase in internal resistance while suppressing a decrease in energy density.

The upper limit of the solid electrolyte/electrode active material ratio cannot be generalized because it varies depending on the type of solid electrolyte and electrode active material used, the content of the solid electrolyte and electrode active material in the electrode active material, etc. , for example, 3 or less.

The amount of volume change due to charging and discharging of the electrode active material contained in the electrode active material layer can be determined by the following method.
(i) The electrode active material in the lithium ion occlusion state and desorption state is measured using an X-ray diffraction device (XRD-6100 manufactured by Shimadzu Corporation, radiation source: Cu-Kα).
(ii) The lattice volumes of the electrode active material in the occlusion state and the desorption state are calculated from the X-ray diffraction pattern, and the volume change rate of the electrode active material due to charging and discharging is determined.
(iii) Using the obtained volume change rate of the electrode active material, calculate the volume change amount of the electrode active material due to charging and discharging in the electrode active material layer.

The amount of change in volume of the solid electrolyte contained in the electrode active material can be determined by the following method.
(i) The bulk modulus of the solid electrolyte (if two or more types are used, a mixture thereof) is measured using a bulk modulus measuring device.
(ii) The amount of change in volume of the solid electrolyte is calculated from the following formula.

(electrode active material)
The positive electrode active material is not particularly limited, but may include layered rock salt type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , Li(Ni-Mn-Co)O ₂ , LiMn ₂ O ₄ , LiNi _0.5 Examples include spinel-type active materials such as Mn _1.5 O ₄ , olivine-type active materials such as LiFePO ₄ and LiMnPO ₄ , and Si-containing active materials such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ . Further, examples of oxide active materials other than those mentioned above include Li ₄ Ti ₅ O ₁₂ .

Further, as the positive electrode active material, a positive electrode active material containing sulfur can be used. In addition to elemental sulfur (S), positive electrode active materials containing sulfur include particles or thin films of organic sulfur compounds or inorganic sulfur compounds. Any material that can occlude lithium ions during discharge may be used. Examples of the organic sulfur compound include disulfide compounds, sulfur-modified polyacrylonitrile represented by the compound described in International Publication No. 2010/044437 pamphlet, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polysulfide carbon, and the like. Among these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubeanic acid are preferred, and sulfur-modified polyacrylonitrile is particularly preferred. As the disulfide compound, those having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group are more preferable. Here, the sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms, which is obtained by mixing sulfur powder and polyacrylonitrile and heating the mixture under an inert gas or reduced pressure. The estimated structure can be found, for example, in Chem. Mater. As shown in 2011, 23, 5024-5028, polyacrylonitrile is ring-closed to become polycyclic, and at least a part of S is bonded to C. The compound described in this document has strong peak signals near 1330 cm ^-1 and 1560 cm ^-1 in the Raman spectrum, and peaks near 307 cm ^-1 , 379 cm ^-1 , 472 cm ^-1 , and 929 cm ^-1 do. On the other hand, inorganic sulfur compounds are preferred because of their excellent stability. Specifically, elemental sulfur (S), S-carbon composite, TiS ₂ and FeS ₂ are more preferred, and elemental sulfur (S) is particularly preferred. Here, the S-carbon composite includes sulfur powder and a carbon material, and is in a composite state by subjecting them to heat treatment or mechanical mixing. More specifically, a state in which sulfur is distributed on the surface and within the pores of a carbon material; a state in which sulfur and carbon material are uniformly dispersed at the nano level, and they aggregate to form particles; a state in which fine sulfur A state in which carbon material is distributed on the surface or inside of the powder; or a state in which multiple of these states are combined.

In some cases, two or more types of positive electrode active materials may be used together. Note that, of course, positive electrode active materials other than those mentioned above may be used.

In a preferred embodiment, the all-solid-state battery according to the first embodiment has a positive electrode active material layer containing a positive electrode active material and a solid electrolyte, in which the positive electrode is disposed on the surface of a current collector, from the viewpoint of output characteristics, The positive electrode active material includes a composite oxide (for example, LiCoO ₂ ) containing lithium and cobalt.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but for example, it is preferably within the range of 40 to 99% by mass, and preferably within the range of 50 to 90% by mass. More preferably, it is within the range of 55 to 80% by mass.

Examples of negative electrode active materials include, but are not limited to, carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Furthermore, examples of metal oxides include Nb ₂ O ₅ , Li ₄ Ti ₅ O ₁₂ , and SiO. Further, examples of the metal active material include simple metals such as In, Al, Si, and Sn, and alloys such as TiSi and La ₃ Ni ₂ Sn ₇ . Furthermore, a metal containing Li may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it contains Li, and examples include Li metal and Li-containing alloys. Examples of Li-containing alloys include alloys of Li and at least one of In, Al, Si, and Sn.

In some cases, two or more types of negative electrode active materials may be used together. Note that, of course, negative electrode active materials other than those mentioned above may be used.

The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but for example, it is preferably within the range of 40 to 99% by mass, and preferably within the range of 50 to 90% by mass. More preferably, it is within the range of 50 to 80% by mass.

Examples of the shape of the electrode active material (positive electrode active material/negative electrode active material) include particulate (spherical, fibrous), thin film, and the like. When the negative electrode active material has a particle shape, the average particle size (D ₅₀ ) is, for example, preferably within the range of 1 nm to 100 μm, more preferably within the range of 10 nm to 50 μm, and even more preferably 100 nm. 20 μm, particularly preferably 1 to 20 μm. Note that in this specification, the value of the average particle diameter (D ₅₀ ) of the electrode active material can be measured by a laser diffraction scattering method.

(solid electrolyte)
Examples of solid electrolytes include sulfide solid electrolytes, resin solid electrolytes, and oxide solid electrolytes.

As the solid electrolyte, a solid electrolyte having a desired volume change can be appropriately selected according to the volume change due to charging and discharging of the electrode active material used.

In one embodiment of the first form, the solid electrolyte preferably includes a resin solid electrolyte from the viewpoint of being able to follow changes in volume of the electrode active material due to charging and discharging.

Examples of the resin solid electrolyte include fluororesin, polyethylene oxide, polyacrylonitrile, polyacrylate, derivatives thereof, and copolymers thereof.

Examples of fluororesins include fluororesins containing vinylidene fluoride (VdF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), derivatives thereof, and the like as constituent units. Specifically, homopolymers such as polyvinylidene fluoride (PVdF), polyhexafluoropropylene (PHFP), and polytetrafluoroethylene (PTFE), binary copolymers such as a copolymer of VdF and HFP, etc. Can be mentioned.

In one embodiment of the first mode, the solid electrolyte is preferably a sulfide solid electrolyte containing S element, more preferably S element, from the viewpoint of being able to follow the volume change of the electrode active material due to charging and discharging. , a sulfide solid electrolyte containing Li and P elements.

The sulfide solid electrolyte may have a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. Examples of the sulfide solid electrolyte having a Li ₃ PS ₄ skeleton include LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _{4, and} Li ₃ PS ₄ . Further, examples of the sulfide solid electrolyte having a Li ₄ P ₂ S ₇ skeleton include a Li-P-S solid electrolyte called LPS. Further, as the sulfide solid electrolyte, for example, LGPS expressed by Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0<x<1) or the like may be used. More specifically, for example, Li ₂ SP ₂ S ₅ , Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S, Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₀ GeP ₂ S ₁₂ , or Li ₆ PS ₅ X (where X is Cl, Br or I), and the like. Note that the description “Li ₂ SP ₂ S ₅ ” means a sulfide solid electrolyte made using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to other descriptions. Among these, the sulfide solid electrolyte is preferably Li 6 PS ₅ X (hereinafter referred to as Li ₆ PS 5 and X is Cl, Br or I), Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S and Li ₃ PS ₄ .

(Conductivity aid and binder)
In addition to the electrode active material and the solid electrolyte, the electrode active material layer may further contain at least one of a conductive additive and a binder.

Examples of conductive aids include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium; alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-grown carbon fibers); (VGCF), polyacrylonitrile carbon fiber, pitch carbon fiber, rayon carbon fiber, activated carbon fiber, etc.), carbon nanotubes (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark)) , furnace black, channel black, thermal lamp black, etc.), but are not limited to these. Further, a particulate ceramic material or resin material coated with the above metal material by plating or the like can also be used as a conductive aid. Among these conductive additives, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon; , silver, gold, and carbon, and more preferably carbon. These conductive aids may be used alone or in combination of two or more.

The shape of the conductive aid is preferably particulate or fibrous. When the conductive additive is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, flake, spindle, etc. I don't mind.

The average particle diameter (primary particle diameter) when the conductive additive is in the form of particles is not particularly limited, but from the viewpoint of the electrical characteristics of the battery, it is preferably 0.01 to 10 μm. In addition, in this specification, "particle diameter of a conductive aid" means the maximum distance L among the distances between arbitrary two points on the outline of a conductive aid. The value of the "average particle diameter of the conductive aid" is the particle diameter of particles observed in several to several dozen fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value shall be adopted.

When the electrode active material layer contains a conductive additive, the content of the conductive additive in the electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass based on the total mass of the electrode active material layer. , more preferably 2 to 8% by weight, and still more preferably 4 to 7% by weight. Within this range, it becomes possible to form a stronger electron conduction path in the electrode active material layer, and it is possible to effectively contribute to improving battery characteristics.

Although the binder is not particularly limited, examples of the binder include the following materials.

Polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, Polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and hydrogenated products thereof , thermoplastic polymers such as styrene-isoprene-styrene block copolymers and their hydrogenated products, tetrafluoroethylene-hexafluoropropylene copolymers (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA) , fluororesins such as ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride- Hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber ( Examples include vinylidene fluoride-based fluororubbers such as VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), and epoxy resins. Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferred.

The thickness of the electrode active material layer varies depending on the structure of the intended all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

From the viewpoint of improving the energy density of the all-solid-state battery, the porosity of the electrode active material layer is preferably 20% or less, more preferably 18% or less, and still more preferably 15% or less. The lower limit is not particularly limited, but is preferably 5% or more.

[Solid electrolyte layer]
The solid electrolyte layer is a layer interposed between the positive electrode active material layer and the negative electrode active material layer, and contains a solid electrolyte (usually as a main component). Since the specific form of the solid electrolyte contained in the solid electrolyte layer is the same as that described above, detailed explanation will be omitted here.

The content of the solid electrolyte in the solid electrolyte layer is preferably within the range of 10 to 100% by mass, and more preferably within the range of 50 to 100% by mass, based on the total mass of the solid electrolyte layer. It is preferably in the range of 90 to 100% by mass.

The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above. Since the specific form of the binder that can be contained in the solid electrolyte layer is the same as that described above, detailed explanation will be omitted here.

The thickness of the solid electrolyte layer varies depending on the structure of the intended all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

A second aspect of the present invention is characterized in that the ratio of the volume change of the solid electrolyte layer to the volume change of the electrode active material layer during charging and discharging is 1 or more. In this specification, the ratio of the volume change of the solid electrolyte to the volume change of the electrode active material due to charging and discharging is also referred to as "solid electrolyte layer/electrode active material layer ratio." Moreover, in the all-solid-state battery according to the second embodiment, at least one of the positive electrode and the negative electrode preferably has the above-mentioned electrode active material layer from the viewpoint of further suppressing an increase in internal resistance.

By controlling the ratio of solid electrolyte layer/electrode active material layer to 1 or more, the solid electrolyte layer can be elastically deformed ( By increasing the volume (increase in volume), it is possible to suppress a decrease in reactivity between the electrodes. Therefore, it is possible to suppress an increase in internal resistance while suppressing a decrease in energy density.

The upper limit of the solid electrolyte layer/electrode active material layer ratio varies depending on the type of solid electrolyte and electrode active material used, the content of the solid electrolyte and electrode active material in the electrode active material, and so it cannot be generalized. No, but for example 3 or less.

Volume changes of the electrode active material layer and solid electrolyte layer due to charging and discharging are calculated by image analysis of optical micrographs of the electrode active material layer and solid electrolyte layer in fully charged and fully discharged states. can do.

In one embodiment of the second form, the solid electrolyte preferably includes a resin solid electrolyte from the viewpoint of being able to follow the volume change of the electrode active material layer due to charging and discharging.

Further, in an embodiment of the second mode, the solid electrolyte is preferably a sulfide solid electrolyte containing S element, and more preferably is a sulfide solid electrolyte containing S element, Li element and P element, more preferably Li ₆ PS ₅ X (here, X is Cl, Br or I), Li ₇ P ₃ S ₁₁ , Li _{3 .2} P _0.96 S and Li ₃ PS ₄ .

Note that in the all-solid-state battery according to the first embodiment, the solid electrolyte layer preferably has the same characteristics as the solid electrolyte layer according to the second embodiment from the viewpoint of further suppressing an increase in internal resistance.

[Positive current collector plate and negative current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries may be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, carbon-coated aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. Note that the positive electrode current collector plate 25 and the negative electrode current collector plate 27 may use the same material or different materials.

[Positive lead and negative lead]
Further, although not shown, the current collector 11 and the current collecting plates (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As constituent materials for the positive electrode and negative electrode leads, materials used in known lithium ion secondary batteries can be similarly employed. In addition, the parts taken out from the exterior are covered with heat-resistant insulating heat-shrinkable material to prevent them from contacting peripheral equipment or wiring and causing electrical leakage, which may affect products (e.g., automobile parts, especially electronic equipment, etc.). Preferably, it is covered with a tube or the like.

[Battery exterior body]
As the battery exterior body, a known metal can case can be used, or a bag-shaped case using a laminate film 29 containing aluminum that can cover the power generating element as shown in FIG. 1 can be used. The laminate film may be, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order, but is not limited thereto. A laminate film is desirable from the viewpoint that it has high output and excellent cooling performance, and can be suitably used in batteries for large equipment such as EVs and HEVs. Moreover, the exterior body is more preferably a laminate film containing aluminum because the group pressure applied to the power generation element from the outside can be easily adjusted.

The all-solid-state lithium ion secondary battery of this embodiment has a configuration in which a plurality of cell layers are connected in series, and thus has excellent output characteristics at a high rate. Therefore, the all-solid-state lithium ion secondary battery of this embodiment is suitably used as a power source for driving EVs and HEVs.

FIG. 5 is a perspective view showing the appearance of a stacked all-solid-state lithium ion secondary battery according to an embodiment of the present invention.

As shown in FIG. 5, the flat stacked secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for extracting power are pulled out from both sides of the battery. There is. The power generation element 57 is surrounded by the battery exterior body (laminate film 52) of the laminated secondary battery 50, and the periphery thereof is heat fused, and the power generation element 57 has a positive electrode tab 58 and a negative electrode tab 59 pulled out to the outside. It is sealed in a sealed condition. Here, the power generation element 57 corresponds to the power generation element 21 of the stacked secondary battery 10a shown in FIG. 1 described above. The power generation element 57 is formed by laminating a plurality of unit cell layers (single cells) 19 each including a positive electrode (positive electrode active material layer) 13, a solid electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

Note that the all-solid-state battery of this embodiment is not limited to a flat battery. A wound type all-solid-state battery may have a cylindrical shape, or may be a cylindrical shape transformed into a rectangular flat shape, etc. There are no particular restrictions. The above-mentioned cylindrical shape is not particularly limited, and its exterior body may be made of a laminate film or a conventional cylindrical can (metal can). Preferably, the power generation element is packaged with an aluminum laminate film. With this form, weight reduction can be achieved.

Furthermore, there is no particular restriction on how to take out the tabs 58 and 59 shown in FIG. 5. The positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type all-solid-state battery, the terminals may be formed using, for example, a cylindrical can (metal can) instead of a tab.

[Assembled battery]
A battery pack is made up of multiple batteries connected together. Specifically, it is configured by using at least two or more, serially or parallelly, or both. By connecting them in series or parallel, it becomes possible to freely adjust the capacity and voltage.

A plurality of batteries can be connected in series or in parallel to form a small detachable battery pack. By connecting multiple small, removable battery packs in series or in parallel, high-capacity, high-capacity power supplies suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric power density can be created. It is also possible to form a battery pack with an output. How many batteries to connect to make a battery pack, and how many stages of small battery packs to stack to make a large-capacity battery pack depends on the battery capacity of the vehicle (electric vehicle) in which it will be mounted. You can decide according to the output.

[vehicle]
The all-solid-state battery according to this embodiment has a high energy density per volume. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required compared to applications in electric and portable electronic devices. Therefore, the all-solid-state battery according to this embodiment can be suitably used as a vehicle power source, for example, as a vehicle drive power source or an auxiliary power source.

Specifically, a battery or a battery pack formed by combining a plurality of batteries can be mounted on the vehicle. According to the present invention, a high-capacity battery with excellent output characteristics can be constructed, and when such a battery is installed, a plug-in hybrid electric vehicle with a long EV driving distance or an electric vehicle with a long driving distance on one charge can be constructed. Batteries or assembled batteries made by combining multiple of these can be used, for example, in the case of automobiles, such as hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (passenger cars, commercial vehicles such as trucks, buses, light vehicles, etc.), etc. , two-wheeled vehicles (including motorcycles, and three-wheeled vehicles)), it is possible to create a vehicle with a long mileage. However, the application is not limited to automobiles; for example, it can be applied to various power sources for other vehicles, such as trains, and on-board power sources such as uninterruptible power supplies. It is also possible to use it as

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the technical scope of the present invention is not limited only to the following examples. In addition, in the following, the instruments and devices used in the glove box were sufficiently dried in advance.

<Example>
(Preparation of positive electrode mixture)
In the glove box, 60 mg of LiCoO ₂ (LCO) (trade name "Cellseed C-5H", manufactured by Nihon Kagaku Kogyo Co., Ltd., average particle size: 7 μm) as a positive electrode active material, 34 mg of Li ₆ PS ₅ Cl as a solid electrolyte, and 6 mg of acetylene black (AB) (trade name "Denka Black (registered trademark) HS-100", manufactured by Denka Co., Ltd., average primary particle diameter: 36 nm) was weighed as a conductive additive. These were placed in a sample bottle containing an agate ball and mixed gently with a spatula. The sample bottle was sealed with Parafilm and mixed using a table mill to obtain a positive electrode mixture.

(Preparation of battery)
An all-solid-state lithium ion secondary battery was fabricated by placing the positive electrode mixture prepared above and a Li-In electrode as a counter electrode facing each other, with a solid electrolyte layer interposed therebetween.

Specifically, 80 mg of solid electrolyte (Li ₁₀ GeP ₂ S ₁₂ (LGPS)) was weighed, put into a PET tube, the surface was smoothed, and the solid electrolyte was pressurized at 400 MPa using a fastening jig. A pellet was prepared. The surface area of the produced solid electrolyte pellet was 0.817 cm ² (pellet diameter φ=1.02 cm). Further, the thickness of the solid electrolyte layer was measured from the change in thickness before and after fabrication, and was found to be 600 μm.

Thereafter, the fastening jig was removed, 6 mg of the positive electrode mixture was placed on one side of the pellet, and pressure was applied at 200 MPa using the fastening jig to produce a positive electrode active material layer. A counter Li--In electrode was placed on the other side of the pellet and pressurized at 100 MPa using a fastening jig to produce an all-solid-state battery evaluation cell. An all-solid-state lithium ion secondary battery was manufactured by restraining the manufactured all-solid-state battery evaluation cell with a restraining pressure of 80 MPa using a fastening jig. Note that the thickness of the positive electrode active material layer was 25 μm. The Li-In electrode used as the negative electrode is a laminate of Li metal foil (diameter 5 mm, thickness 100 μm, manufactured by Honjo Metal Co., Ltd.) and In metal foil (diameter 9 mm, thickness 100 μm, manufactured by Nilaco Co., Ltd.). The Li--In electrode was arranged so that the In metal foil was located on the solid electrolyte layer side.

<Comparative example>
An all-solid-state lithium ion secondary battery was prepared in the same manner as in the example except that Li ₁₀ GeP ₂ S ₁₂ (LGPS) was used instead of Li ₆ PS ₅ Cl as the solid electrolyte in preparing the positive electrode mixture. did.

<Method for measuring physical properties>
(Volume change of positive electrode active material due to charging and discharging)
Regarding LiCoO ₂ (LCO) used as the positive electrode active material, the volume change due to charging and discharging was measured by the following method.
(i) LCO in the occlusion state and desorption state of lithium ions was measured using an X-ray diffraction device (XRD-6100 manufactured by Shimadzu Corporation, radiation source: Cu-Kα).
(ii) The lattice volumes of LCO in the occlusion state and desorption state were calculated from the X-ray diffraction pattern, and the volume change rate of LCO due to charging and discharging was determined.
(iii) Using the obtained volume change rate of LCO, the volume change amount of LCO accompanying charging and discharging in the positive electrode active material layer was calculated.

(Volume change amount of solid electrolyte)
The bulk modulus of Li ₆ PS ₅ Cl and Li ₁₀ GeP ₂ S ₁₂ (LGPS) used as the solid electrolyte was measured using a bulk modulus measuring device. The volume changes of Li ₆ PS ₅ Cl and Li ₁₀ GeP ₂ S ₁₂ (LGPS) were calculated from the following formula.

Table 1 shows the ratio of the volume change of the solid electrolyte to the volume change of the positive electrode active material due to charging and discharging in the positive electrode active material layer (volume change of the positive electrode active material/volume change of the solid electrolyte).

<Characteristics evaluation of all-solid-state lithium ion secondary battery>
Rate characteristics of each all-solid lithium ion secondary battery produced in Examples and Comparative Examples were evaluated according to the following charge/discharge test conditions.

(Charge/discharge test conditions)
1) Charge/discharge conditions [Voltage range] 1.9 to 3.6V
[Charging process] 0.2C CCCV (CV: 0.01C)
[Discharge process] 10C CCCV (CV: 0.05C)
(30 minutes pause each after charging and discharging)
2) Evaluation temperature: 298K (25°C).

The evaluation cell was placed in a constant temperature bath set at the above evaluation temperature using a charge/discharge tester at constant current and constant voltage (CCCV) during the charging process (the process of inserting Li into the evaluation electrode). ) mode and charged from 1.9V to 3.6V at 0.2C. Thereafter, in the discharge process (referring to the Li desorption process from the evaluation electrode), the battery was discharged from 3.6V to 1.9V at 10C in constant current/constant voltage (CCCV) mode. Note that 1C here refers to the current value at which the battery becomes fully charged (100% charged) when charged for one hour at that current value.

The obtained discharge curve (horizontal axis: depth of discharge (DOD), vertical axis: cell voltage [V]) is shown in FIG.

From the results shown in Table 1 and FIG. 6, the all-solid-state lithium ion secondary battery of the Example according to the present invention suppresses the voltage drop at the end of discharge more than the Comparative Example, and therefore suppresses the increase in internal resistance. It turns out that it can be suppressed.

10a, 50, 100 stacked secondary battery,
10b bipolar secondary battery,
11 current collector,
11′ positive electrode current collector,
11'' negative electrode current collector,
11a outermost layer current collector on the positive electrode side,
11b outermost layer current collector on the negative electrode side,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 solid electrolyte layer,
19 cell layer,
21, 57 Power generation element,
23 bipolar electrode,
25 Positive electrode current collector plate (positive electrode tab),
27 Negative electrode current collector plate (negative electrode tab),
29, 52 Laminated film,
58 Positive electrode tab,
59 negative electrode tab,
200 Metal plate 300 Bolt 400 Nut.

Claims (5)

A power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and a restraining member that restrains the power generation element in a stacking direction,
At least one of the positive electrode and the negative electrode has an electrode active material layer containing an electrode active material and a solid electrolyte disposed on the surface of a current collector,
In the electrode active material layer, the ratio of the volume change of the solid electrolyte to the volume change of the electrode active material due to charging and discharging is 1 or more,
An all-solid-state battery, wherein the solid electrolyte included in the electrode active material layer is Li ₆ PS ₅ X (where X is Cl, Br, or I). The all-solid-state battery according to claim 1, wherein the solid electrolyte included in the electrode active material layer does not include a resin solid electrolyte. The all-solid-state battery according to claim 1 or 2, wherein the electrode active material layer consists of the solid electrolyte, the electrode active material, and at least one of a conductive additive and a binder. The positive electrode has a positive electrode active material layer containing a positive electrode active material and a solid electrolyte disposed on the surface of a current collector,
The all-solid-state battery according to claim 1, wherein the positive electrode active material includes a composite oxide containing lithium and cobalt. A power generation element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and a restraining member that restrains the power generation element in a stacking direction,
The ratio of the volume change of the solid electrolyte layer to the volume change of the electrode active material layer constituting the positive electrode and the negative electrode due to charging and discharging is 1 or more,
An all-solid-state battery, wherein the solid electrolyte included in the solid electrolyte layer is Li ₆ PS ₅ X (where X is Cl, Br, or I).