JP2022110345A - secondary battery - Google Patents

Abstract

To provide means capable of preventing cracks in an electrode active material or a solid electrolyte due to volume expansion of the electrode active material while suppressing a decrease in energy density in a secondary battery.SOLUTION: In a secondary battery that includes a power generation element including 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 the stacking direction, and further includes an electrode active material layer containing an electrode active material and a solid electrolyte in which at least one of the positive electrode and the negative electrode is disposed on the surface of a current collector, the sum of the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery and the restraining pressure applied by the restraining member is smaller than the yield stress of the electrode active material or the solid electrolyte.SELECTED DRAWING: Figure 1

Description

The present invention relates to secondary batteries.

In recent years, in order to cope with global warming, reduction of carbon dioxide emissions is earnestly desired. In the automobile industry, expectations are gathering for the reduction of carbon dioxide emissions through the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV). Development of electrolyte secondary batteries has been actively carried out.

Secondary batteries for motor driving 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 among all practical batteries, have attracted attention and are being rapidly developed.

Lithium ion secondary batteries, which are currently in widespread use, use a combustible organic electrolyte as an electrolyte. Such a liquid type lithium ion secondary battery requires stricter safety measures against liquid leakage, short circuit, overcharge, etc. than other batteries.

Therefore, in recent years, extensive research and development has been made on all-solid lithium secondary batteries using oxide-based or sulfide-based solid electrolytes. A solid electrolyte is a material composed mainly of an ionic conductor capable of conducting ions in a solid. Therefore, in the all-solid lithium secondary battery, in principle, various problems due to the combustible organic electrolytic solution do not occur unlike the conventional liquid-type lithium ion secondary battery. In general, the use of a high-potential, large-capacity positive electrode material and a large-capacity negative electrode material can significantly improve the output density and energy density of the battery.

By the way, the electrode active material undergoes a volume change as it is charged and discharged. In all-solid-state lithium secondary batteries, the electrode active material layer contains a solid electrolyte in addition to the electrode active material, but this electrolyte is solid and does not easily follow changes in volume of the electrode active material. Therefore, when the stress generated in the solid electrolyte increases during charging and discharging, cracks may occur in the particles of the solid electrolyte, leading to an increase in the internal resistance of the battery and a decrease in cycle durability. Here, as a technique for mitigating the effect of volume expansion of an electrode active material during charging and discharging of a battery, for example, Patent Document 1 discloses an active material, a sulfide solid electrolyte, and a hydrogenated rubber material that binds them together. An all-solid-state lithium secondary battery is disclosed having an electrode layer therein.

JP 2011-134675 A

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

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide means capable of preventing cracks from occurring in an electrode active material or a solid electrolyte due to volume expansion of the electrode active material while suppressing a decrease in the energy density of a secondary battery. and

The present inventors have made intensive studies to solve the above problems. As a result, in a secondary battery including a power generation element including positive and negative electrodes and a restraining member that restrains the power generation element in the stacking direction, an electrode active material layer containing an electrode active material and a solid electrolyte is formed during charge and discharge of the battery. The sum of the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material and the restraining pressure applied by the restraining member is smaller than the yield stress of the electrode active material or the solid electrolyte. The present inventors have found that the above problems can be solved by configuring so as to complete the present invention.

That is, one embodiment of the present invention provides a secondary 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 the stacking direction. Regarding batteries. Here, 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. Further, the sum of the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery and the restraining pressure applied by the restraining member is equal to the electrode active material or the It is also characterized in that it is configured to be smaller than the yield stress of the solid electrolyte.

According to the present invention, it is possible to prevent cracks from occurring in the electrode active material or the solid electrolyte due to the volume expansion of the electrode active material while suppressing the decrease in the energy density of the secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view schematically showing a stacked (internal parallel connection type) all-solid-state lithium secondary battery that is an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing a stacked (internal parallel connection type) all-solid lithium secondary battery that is an embodiment of the present invention. It is the side view seen from the A direction shown in FIG. 4 is a graph showing how the permissible upper limit of the confining pressure changes when the bulk elastic modulus of the solid electrolyte changes when the electrode active material and its volume fraction used in Example 1 described later are used. . FIG. 4 plots the relationship between the bulk elastic modulus and the confining pressure of the solid electrolytes in Example 1 and Comparative Example 1. In FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the appearance of a stacked all-solid lithium secondary battery that is an embodiment of the present invention; 10 is a graph showing how the permissible upper limit of the confining pressure changes when the bulk elastic modulus of the solid electrolyte changes when the electrode active material and its volume fraction used in Example 2, which will be described later, are used. . FIG. 6 plots the relationship between the bulk elastic modulus and the confining pressure of the solid electrolytes in Example 2 and Comparative Example 2. In FIG.

One embodiment of the present invention includes a power generating 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 generating element in a stacking direction, At least one of the negative electrodes has an electrode active material layer containing an electrode active material and a solid electrolyte, and the maximum value of the internal pressure of the electrode active material layer caused by volume expansion of the electrode active material due to charging and discharging of the battery; In the secondary battery, the sum of the restraining pressure applied by the restraining member is smaller than the yield stress of the electrode active material or the solid electrolyte. According to the secondary battery according to the present embodiment, it is possible to prevent the occurrence of cracks in the electrode active material or the solid electrolyte due to the volume expansion of the electrode active material while suppressing the decrease in the energy density of the secondary battery. .

Hereinafter, the present embodiment will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of 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 lithium secondary battery (hereinafter also simply referred to as a “stacked secondary battery”) that is an embodiment of the present invention. It is a sectional view. A laminated secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which charge/discharge reactions actually progress is sealed inside a laminate film 29 that is a battery exterior body. In addition, in the stacked secondary battery 10a, a restraining pressure is applied in the stacking direction of the power generating 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 laminated secondary battery 10a of the present embodiment includes a negative electrode in which negative electrode active material layers 13 are arranged on both sides of a negative electrode current collector 11′, a solid electrolyte layer 17, and a positive electrode. It has a configuration in which a positive electrode having positive electrode active material layers 15 disposed on both sides of a current collector 11″ is laminated. Specifically, one negative electrode active material layer 13 and a positive electrode active material layer adjacent thereto are laminated. The negative electrode, the solid electrolyte layer and the positive electrode are laminated in this order such that the electrodes 15 face each other with the solid electrolyte layer 17 interposed therebetween. It constitutes the battery 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 single cell layers 19 are stacked and electrically connected in parallel. The negative electrode active material layer 13 is arranged only on one side of each of the outermost negative electrode current collectors positioned on both outermost layers of the power generating element 21, but the active material layer may be provided on both sides. Instead of using a current collector exclusively for the outermost layer having an active material layer on only one side, a current collector having active material layers on both sides may be used as it is as the current collector for the outermost layer. By reversing the arrangement of the positive electrode and the negative electrode from 1, the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 21, and the positive electrode is placed on one or both sides of the outermost positive electrode current collector. An active material layer may be arranged.

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

In the above description, an embodiment of the all-solid-state battery according to one aspect of the present invention has been described by taking a stacked (internal parallel connection type) all-solid-state lithium-ion secondary battery as an example. However, the type of all-solid-state battery to which the present invention can be applied is not particularly limited. It can also be applied to a bipolar all-solid-state battery that includes a bipolar electrode having a bonded negative electrode active material layer.

FIG. 2 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. 3 is a side view seen from direction A shown in FIG. 2. FIG.

As shown in FIGS. 2 and 3, the laminated secondary battery 10a according to the present embodiment includes a power generation element 21 sealed with the laminate film 29 shown in FIG. 1 and a power generation element sealed with the laminate film 29. 21, and bolts 300 and nuts 400 as fastening members. The fastening members (bolts 300 and nuts 400) have the function of fixing the metal plate 200 while sandwiching the power generating element 21 sealed with the laminate film 29. As shown in FIG. As a result, the metal plate 200 and the fastening members (bolts 300 and nuts 400) function as restraining members that restrain (pressurize) the power generating elements 21 in the stacking direction. Note that the restraining member is not particularly limited as long as it is a member capable of restraining the power generating elements 21 in the stacking direction. As a restraining member, a combination of a plate made of a rigid material such as the metal plate 200 and the above-described fastening member is typically used. 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 portion of the metal plate 200 so as to restrain the power generation element 21 in the stacking direction may be used.

The lower limit of the load applied to the power generating element 21 (constraining pressure in the stacking direction of the power generating element) 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.

Main components of the above-described stacked secondary battery 10a will be described below.

[Current collector]
The current collector has the function of mediating electron transfer between the active material layer and an external load or power source. There are no particular restrictions on the material that constitutes the current collector. As the constituent material of the current collector, for example, a metal or a conductive resin can be used.

Specifically, examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or the like may be used. Alternatively, a foil in which a metal surface is coated with aluminum may be used. Among them, aluminum, stainless steel, copper, and nickel are preferable from the viewpoint of electronic conductivity, battery operating potential, adhesion of the negative electrode active material to the current collector by sputtering, and the like.

As the latter conductive resin, a resin obtained by adding a conductive filler to a non-conductive polymeric material as necessary can be used.

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), and polyimide. (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA), polymethylmethacrylate (PMMA) , polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials can have excellent electrical potential or solvent resistance.

Conductive fillers may be added to the 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 of only a non-conductive polymer, a conductive filler is inevitably essential in order to impart conductivity to the resin.

Any electrically conductive filler can be used without particular limitation. Examples of materials having excellent conductivity, potential resistance, or lithium ion blocking properties include metals and conductive carbon. 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 these metals. It preferably contains alloys or metal oxides. Also, the conductive carbon is not particularly limited. 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. At least one type is included.

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

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. Moreover, from the viewpoint of blocking movement of lithium ions between the single 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 that constitute the secondary battery according to the present embodiment has an electrode active material layer containing an electrode active material and a solid electrolyte. The electrode active material layer is typically arranged on the surface of the current collector as shown in FIG. It is also possible for the electrode active material layer itself to constitute an electrode without using a current collector.

In the secondary battery according to the present embodiment, 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, items common to the positive electrode and the negative electrode are referred to as "electrode" unless otherwise specified.

In the secondary battery according to the present embodiment, in the electrode active material layer having the above configuration, the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery, and the It is characterized in that the sum of the restraining pressure applied by the restraining member is smaller than the yield stress of the electrode active material or the solid electrolyte. With such a configuration, even if the electrode active material expands in volume as the battery is charged and discharged, the stress generated in the electrode active material and/or the solid electrolyte contained in the electrode active material layer is reduced. It never exceeds the yield stress of these materials. Therefore, it is possible to prevent the occurrence of cracks in the electrode active material or the solid electrolyte due to volume expansion of the electrode active material due to charge/discharge of the battery. Note that, according to the configuration according to the present embodiment, it is not necessary to use a material that lowers the energy density of the battery, such as the hydrogenated rubber material described in Patent Document 1 mentioned above. Therefore, there is an advantageous effect not disclosed in Patent Document 1 in that it is possible to prevent cracks from occurring in the electrode active material or the solid electrolyte while minimizing the decrease in the energy density of the battery. .

Here, the “internal pressure of the electrode active material layer due to volume expansion of the electrode active material due to charging/discharging of the battery” means that when the battery is charged/discharged without applying a confining pressure to the power generation element, means the internal pressure of the electrode active material layer. Further, "the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery" usually means This is the internal pressure of the electrode active material layer when the volume expansion of the active material reaches its maximum. The specific value of "the maximum value of the internal pressure of the electrode active material layer caused by the volume expansion of the electrode active material due to charging and discharging of the battery" can be directly determined using a pressure measuring means such as a pressure sensor. may be obtained either directly or indirectly by other methods. As for the method of indirectly obtaining this value, FIG. Description will be made with reference to this. FIG. 4 shows how the allowable upper limit of the confining pressure changes when the bulk elastic modulus of the solid electrolyte changes when the electrode active material and its volume fraction used in Example 1, which will be described later, are used. It is a graph showing.

Here, first, the yield stress in the bulk state of the solid electrolyte contained in the electrode active material layer is obtained (one-dot chain line (Y=210 [MPa]) shown in FIG. 4). When the stress generated in the solid electrolyte exceeds this yield stress, cracks occur in the solid electrolyte. On the other hand, ``the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery'' depends on the elasticity of the solid electrolyte, assuming that the type of electrode active material is fixed. varies linearly depending on Specifically, as the bulk elastic modulus of the solid electrolyte increases (that is, as the solid electrolyte becomes a material that is less elastically deformable), the maximum value increases linearly. Therefore, "the sum of the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery and the restraining pressure applied by the restraining member is smaller than the yield stress of the solid electrolyte." The upper limit of the confining pressure that can be allowed to satisfy the condition of is linearly decreased. This is represented by the graph (broken line) shown in FIG. Here, the value of the above-mentioned "maximum value of the internal pressure of the electrode active material layer due to volume expansion of the electrode active material due to charging and discharging of the battery" is the value of the yield stress of the solid electrolyte (Y = 210 [MPa ]) and the graph (broken line) shown in FIG.

From the above, if the values of the bulk elastic modulus and the confining pressure of the solid electrolyte are adopted so as to be plotted in the area surrounded by the graph (dashed line) and the x-axis and y-axis shown in FIG. It becomes possible to manufacture such a secondary battery. As the values of the yield stress and bulk modulus of the solid electrolyte, values measured by the nanoindentation method in accordance with ISO 14577 (instrumented indentation test), as described in the Examples section below, are adopted. shall be

The constituent elements of the electrode active material layer will be described below.

(Electrode active material)
The positive electrode active material is not particularly limited, but contains M1 element and O element as a positive electrode active material with relatively large volume expansion due to charging and discharging, and the M1 element is Li, Mn, Ni, Co, Cr, Fe. and at least one element selected from the group consisting of P. Examples of such positive electrode active materials include layered rock salt type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ and Li(Ni—Mn—Co)O ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _{1 . spinel -} type active materials such as 5O4; olivine _- type active materials such as _LiFePO4 and _LiMnPO4 ; and Si _- containing active materials such as _Li2FeSiO4 and _Li2MnSiO4 . Examples of oxide active materials other than the above include Li ₄ Ti ₅ O ₁₂ and LiVO ₂ . In addition, an organic positive electrode active material may be used as the positive electrode active material that undergoes relatively large volume expansion due to charging and discharging.

Moreover, as the positive electrode active material, a positive electrode active material containing an S element can be used from the viewpoint of improving the energy density of the battery. Examples of the positive electrode active material containing the element S include elemental sulfur (S) and particles or thin films of organic sulfur compounds or inorganic sulfur compounds. However, any material may be used as long as it can absorb lithium ions during discharge. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile represented by compounds described in WO 2010/044437, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polysulfide carbon, and the like. Among them, 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 group, or a thioamide group are more preferred. Here, sulfur-modified polyacrylonitrile is sulfur-atom-containing modified polyacrylonitrile obtained by mixing sulfur powder and polyacrylonitrile and heating the mixture under an inert gas or under reduced pressure. Its putative structure is described, for example, in Chem. Mater. 2011, 23, 5024-5028, polyacrylonitrile is ring-closed to form a polycyclic structure, and at least 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 further peaks near 307 cm ^-1 , 379 cm ^-1 , 472 cm ^-1 and 929 cm ^-1 . do. On the other hand, an inorganic sulfur compound is preferable because of its excellent stability. Specifically, as the positive electrode active material containing the S element, simple sulfur (S), S-carbon composite, TiS ₂ and FeS ₂ are more preferable, and simple sulfur ( S) is particularly preferred. Here, the S-carbon composite includes a sulfur powder and a carbon material, and is in a composite state by subjecting them to heat treatment or mechanical mixing. More specifically, the state in which sulfur is distributed on the surface and in the pores of the carbon material; the state in which sulfur and the carbon material are uniformly dispersed at the nano level and are aggregated into particles; fine sulfur A state in which the carbon material is distributed on the surface or inside the powder; or a state in which a plurality of these states are combined.

In some cases, two or more positive electrode active materials may be used together. It goes without saying that positive electrode active materials other than those described above may be used.

In a preferred embodiment, from the viewpoint of output characteristics, the secondary battery according to the present embodiment includes a positive electrode having 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 active material includes a layered rock salt type active material containing lithium and cobalt (eg, Li(Ni—Mn—Co)O ₂ ).

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, soft carbon, and the like. Moreover, as a metal _oxide , _Nb2O5 , _Li4Ti5O12 , _SiO etc. are _mentioned , for example. Furthermore, examples of metal active materials include simple metals such as In, Al, Si and Sn, and alloys such as TiSi and La ₃ Ni ₂ Sn ₇ . Moreover, you may use the metal containing Li as a negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is an active material containing Li, and examples thereof include Li metal and Li-containing alloys. Li-containing alloys include, for example, alloys of Li and at least one of In, Al, Si and Sn.

In some cases, two or more kinds of negative electrode active materials may be used together. Needless to say, negative electrode active materials other than those described above may be used.

The content of the electrode active material in the electrode active material layer is not particularly limited. More preferably, it is in the range of 45 to 80% by mass. Also, the volume fraction of the electrode active material in the electrode active material layer is not particularly limited, but for example, it is preferably in the range of 30 to 99% by volume, more preferably in the range of 40 to 90% by volume. , 45 to 80% by volume.

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 electrode active material is in the form of particles, the average particle size (D ₅₀ ) thereof is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, still more preferably 100 nm. to 20 μm, particularly preferably 1 to 20 μm. In addition, in this specification, the value of the average particle size ( _D50 ) of the electrode active material can be measured by a laser diffraction scattering method.

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

As the solid electrolyte, a material having a desired bulk elastic modulus can be appropriately selected according to the degree of volume expansion associated with charging and discharging of the electrode active material used.

In a preferred embodiment of the secondary battery according to the present aspect, the solid electrolyte preferably contains a resin solid electrolyte from the viewpoint of being able to follow the volume change of the electrode active material during charging and discharging. Such resin solid electrolytes include fluororesin, polyethylene oxide, polyacrylonitrile, polyacrylate, derivatives thereof and copolymers thereof.

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

In another preferred embodiment of the secondary battery according to the present embodiment, the solid electrolyte is preferably a sulfide solid electrolyte containing an S element from the viewpoint of being able to follow the volume change of the electrode active material due to charging and discharging. more preferably contains Li element, M element and S element, wherein said M element is selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl and I is a sulfide solid electrolyte containing at least one element, more preferably a sulfide solid electrolyte containing S element, Li element and P element.

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 sulfide solid electrolytes 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 sulfide solid electrolytes having a Li ₄ P ₂ S ₇ skeleton include Li—P—S based solid electrolytes called LPS. As the sulfide solid electrolyte, for example, LGPS represented by Li _(4-x) Ge _(1-x) P _x S ₄ (where x satisfies 0<x<1) 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. The description of “Li ₂ SP _{2 S 5 ” means a sulfide solid electrolyte using a raw material composition containing Li 2 S and P 2 S 5 , and} the same applies to other descriptions. Among them, the sulfide solid electrolyte has a high ionic conductivity and a low bulk modulus, so that it can follow the volume change of the electrode active material due to charging and discharging, so Li ₆ PS ₅ X (here and X is _Cl , _Br or I) _{, Li7P3S11 , Li3.2P0.96S} and _Li3PS4 .

The content of the solid electrolyte in the electrode active material layer is not particularly limited, but for example, it is preferably in the range of 1 to 70% by mass, more preferably in the range of 10 to 60% by mass. Preferably, it is more preferably in the range of 20 to 55% by mass. Also, the volume fraction of the electrode active material in the electrode active material layer is not particularly limited, but for example, it is preferably in the range of 1 to 70% by volume, more preferably in the range of 10 to 60% by volume. , 20 to 55% by volume.

(Conductive agent and binder)
The electrode active material layer may further contain at least one of a conductive aid and a binder in addition to the electrode active material and the solid electrolyte. However, in a preferred embodiment, the electrode active material layer does not contain a binder, and in a more preferred embodiment, the electrode active material layer does not contain a conductive aid and a binder.

Examples of conductive aids include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys containing these metals, and metal oxides; carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, activated carbon fiber, etc.), carbon nanotubes (CNT), carbon black (specifically, acetylene black, Ketjenblack (registered trademark) , furnace black, channel black, thermal lamp black, etc.), but are not limited thereto. In addition, 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 aids, 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 at least one 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 agent is particulate, the shape of the particles is not particularly limited, and may be powdery, spherical, rod-like, needle-like, plate-like, columnar, amorphous, scaly, spindle-like, or the like. I don't mind.

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

When the electrode active material layer contains a conductive aid, the content of the conductive aid in the electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass with respect to the total mass of the electrode active material layer. , more preferably 2 to 8% by mass, more preferably 4 to 7% by mass. Within such a range, it becomes possible to form a stronger electron conduction path in the electrode active material layer, which can effectively contribute to the improvement of battery characteristics.

Although the thickness of the electrode active material layer varies depending on the configuration of the intended all-solid-state battery, it is preferably in the range of 0.1 to 1000 μm, for example.

From the viewpoint of improving the energy density of the secondary battery, the porosity of the electrode active material layer is preferably 20% or less, more preferably 18% or less, and even more preferably 15% or less. Although the lower limit is not particularly limited, it 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 described above, detailed description is omitted here.

The content of the solid electrolyte in the solid electrolyte layer is, for example, preferably in the range of 10 to 100% by mass, more preferably in the range of 50 to 100% by mass, relative to the total mass of the solid electrolyte layer. Preferably, it is more 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.

Although the thickness of the solid electrolyte layer varies depending on the desired configuration of the all-solid-state battery, it is preferably in the range of 0.1 to 1000 μm, for example.

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

[Positive lead and negative lead]
Although not shown, the current collectors (11″, 11′) and the current collector plates (27, 25) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent material of the negative electrode lead, materials used in known lithium-ion secondary batteries can be similarly employed.The portion taken out from the exterior may contact peripheral devices, wiring, etc. and cause electric leakage. It is preferable to cover with a heat-resistant insulating heat-shrinkable tube or the like so as not to affect products (for example, automobile parts, especially electronic devices).

[Battery exterior body]
As the battery outer package, a known metal can case can be used, and a bag-like case using a laminate film 29 containing aluminum that can cover the power generation element as shown in FIG. 1 can be used. The laminated film may be, for example, a laminated 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 is excellent in high power output and cooling performance and can be suitably used for batteries for large equipment for EV and HEV. Moreover, since the group pressure applied to the power generating element from the outside can be easily adjusted, the outer package is more preferably a laminate film containing aluminum.

The all-solid-state lithium-ion secondary battery of the present embodiment has a structure 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 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 laminated secondary battery 50 has a rectangular flat shape, and from both sides thereof, a positive electrode tab 58 and a negative electrode tab 59 for extracting electric power are pulled out. there is The power generation element 57 is wrapped by the battery outer body (laminate film 52) of the laminated secondary battery 50, and the periphery thereof is heat-sealed. sealed in place. Here, the power generation element 57 corresponds to the power generation element 21 of the above-described stacked secondary battery 10a shown in FIG. The power generation element 57 is formed by stacking a plurality of single cell layers (single cells) 19 each including a positive electrode (positive electrode active material layer) 15 , a solid electrolyte layer 17 and a negative electrode (negative electrode active material layer) 13 .

Note that the all-solid-state battery of this embodiment is not limited to a flat shape. The wound-type all-solid-state battery may have a cylindrical shape, or may have a flat rectangular shape obtained by deforming such a cylindrical shape. It is not particularly limited. In the case of the cylindrical container, the exterior body may be a laminate film or a conventional cylindrical can (metal can), and is not particularly limited. Preferably, the power generation element is wrapped with an aluminum laminate film. Weight reduction can be achieved by this configuration. Also, the removal of the tabs 58 and 59 shown in FIG. 5 is not particularly limited. 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 pieces and pulled out from each side, as shown in FIG. is not limited to Moreover, in a winding-type all-solid-state battery, instead of tabs, for example, cylindrical cans (metal cans) may be used to form terminals.

As described above, the case where the secondary battery according to the present embodiment is an all-solid lithium secondary battery has been described as an example, but the secondary battery according to the present embodiment may not be an all-solid-state secondary battery. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). The amount of the liquid electrolyte (electrolyte solution) that can be contained in the solid electrolyte layer is not particularly limited, but the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and the liquid electrolyte (electrolyte solution) does not leak. is preferably the amount of As the liquid electrolyte (electrolytic solution), a solution in which a conventionally known lithium salt is dissolved in a conventionally known organic solvent is used. The liquid electrolyte (electrolytic solution) may further contain additives other than the organic solvent and the lithium salt. These additives may be used alone or in combination of two or more. In addition, when the additive is used in the electrolytic solution, the amount used can be appropriately adjusted.

Further, in the above, "the sum of the maximum value of the internal pressure of the electrode active material layer caused by the volume expansion of the electrode active material due to the charging and discharging of the battery and the restraining pressure applied by the restraining member" is the "yield of the solid electrolyte. The explanation has mainly been given for the case where the stress is less than However, if the yield stress of the electrode active material contained in the electrode active material layer is smaller than the yield stress of the solid electrolyte contained in the electrode active material layer, the electrode active material will be added before the solid electrolyte as the total increases. Cracks may occur in Therefore, in such a case, the above-described cracks in the electrode active material can be prevented by constructing the battery so that the total is smaller than the "yield stress of the electrode active material." Such forms are also within the scope of the present invention.

[Assembled battery]
An assembled battery is an object configured by connecting a plurality of batteries. Specifically, at least two or more are used, and serialization or parallelization or both of them are used. By connecting in series and in parallel, it is 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 assembled battery. A plurality of these detachable small battery packs are further connected in series or in parallel to form a large-capacity, large-capacity battery suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric output density. An assembled battery with an output can also be formed. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery, depends on the battery capacity of the vehicle (electric vehicle) in which it is installed. It should be decided 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 sizes are required compared to electrical and portable electronic device applications. Therefore, the all-solid-state battery according to the present embodiment can be suitably used as a power source for vehicles, for example, a power source for driving a vehicle or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, since a high-capacity battery with excellent output characteristics can be configured, a plug-in hybrid electric vehicle with a long EV travel distance or an electric vehicle with a long one-charge travel distance can be configured by mounting such a battery. Batteries or assembled batteries made by combining a plurality of these, for example, in the case of automobiles, hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, buses, light vehicles, etc.) , including two-wheeled vehicles (motorcycles) and tricycles), the vehicle can have 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 moving bodies such as trains, and power sources for installation such as uninterruptible power supplies. It can also be used as

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

<Example 1>
(Preparation of positive electrode mixture)
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material and Li ₆ PS ₅ Br as a solid electrolyte were placed in a glove box, and the volume ratio of the solid electrolyte in the positive electrode mixture was 50% by volume. It was weighed so that These were placed in a sample bottle containing an agate ball and lightly mixed with a spatula. The sample bottle was sealed with parafilm and mixed using a table mill to obtain a positive electrode mixture. Here, the volume elastic moduli of the positive electrode active material and the solid electrolyte used for preparing the positive electrode mixture were 199 [GPa] and 3.29 [GPa], respectively. Moreover, the yield stress of the solid electrolyte was 210 [MPa]. The bulk modulus and yield stress were measured by the nanoindentation method according to ISO14577 (instrumented indentation test).

Then, in the case where the positive electrode active material layer is configured using the positive electrode mixture composition (type and volume ratio of the positive electrode active material and the solid electrolyte), the positive electrode due to volume expansion of the positive electrode active material during charging of the battery Considering the maximum internal pressure of the active material layer, the allowable upper limit of the confining pressure at which cracks do not occur in the solid electrolyte contained in the positive electrode active material layer was experimentally calculated to be 120 [MPa]. That is, if the value of the restraining pressure applied using the fastening member during operation of the battery is less than the allowable upper limit value, the internal pressure of the positive electrode active material layer due to the volume expansion of the positive electrode active material accompanying charging and discharging of the battery. The sum of the maximum value and the confining pressure is smaller than the yield stress of the solid electrolyte. In addition, when the volume modulus of the solid electrolyte is increased from the positive electrode mixture composition described above, the permissible upper limit of the confining pressure at which cracks do not occur in the solid electrolyte gradually decreases. The bulk modulus of the solid electrolyte with the allowable upper limit of zero (0) was calculated to be 8.2 [GPa].

(Production of battery)
An all-solid lithium secondary battery was fabricated by placing the positive electrode mixture prepared above and a Li—In electrode as a counter electrode facing each other and interposing a solid electrolyte layer therebetween.

Specifically, 80 mg of a solid electrolyte (Li ₁₀ GeP ₂ S ₁₂ (LGPS)) was weighed, placed in a PET tube, smoothed on the surface, and pressurized at 400 [MPa] using a fastening jig. to prepare a solid electrolyte pellet.

After that, the fastening jig was pulled out, and 6 mg of the positive electrode mixture was placed on one side of the pellet and pressed at 200 [MPa] using the fastening jig to prepare a positive electrode active material layer. Also, a counter Li—In electrode was placed on the other side of the pellet and pressurized at 100 [MPa] using a fastening jig to fabricate an all-solid battery evaluation cell. Then, the produced all-solid-state battery evaluation cell was constrained with a binding pressure of 65 [MPa] using a fastening jig, thereby producing the all-solid-state lithium secondary battery of this example. The thickness of the positive electrode active material layer was 25 μm. The Li—In electrode used for 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 The Nilaco Corporation). , and the Li—In electrodes were arranged so that the In metal foil was positioned on the solid electrolyte layer side.

In the all-solid lithium secondary battery produced above, cracks do not occur in the solid electrolyte contained in the positive electrode active material layer even after the charge-discharge reaction proceeds. This is because the restraining pressure applied by the fastening member is 65 [MPa], which is smaller than the above-mentioned allowable upper limit (120 [MPa]), and the volume expansion of the positive electrode active material accompanying charging and discharging of the battery. This is because the sum of the maximum value of the internal pressure of the positive electrode active material layer caused by the above-described constraint pressure is smaller than the yield stress of the solid electrolyte contained in the positive electrode active material layer.

<Comparative Example 1>
Except for using Li ₁₀ GeP ₂ S ₁₂ (LGPS) instead of Li ₆ PS ₅ Br as the solid electrolyte contained in the positive electrode active material layer, the same method as in Example 1 described above was used to obtain the comparative example. An all-solid lithium secondary battery was produced (the binding pressure by the fastening jig is 65 [MPa]). The bulk modulus of Li ₁₀ GeP ₂ S ₁₂ (LGPS) was measured using the same method as above and was 37.2 [GPa].

In the all-solid lithium secondary battery produced above, after the charge-discharge reaction proceeds, a large number of cracks occur in the solid electrolyte contained in the positive electrode active material layer. This is because the bulk elastic modulus of the solid electrolyte contained in the positive electrode active material layer is as large as 37.2 [GPa], and the internal pressure of the positive electrode active material layer due to the volume expansion of the positive electrode active material accompanying charging and discharging of the battery increases. This is because the sum of the maximum value and the confining pressure is greater than the yield stress of the solid electrolyte contained in the positive electrode active material layer.

FIG. 4 shows a plot of the relationship between the bulk elastic modulus and the confining pressure of the solid electrolytes in Example 1 and Comparative Example 1 described above.

<Example 2>
Except that the volume ratio of the solid electrolyte in the positive electrode mixture was set to 45% by volume, and the confining pressure by the fastening jig was set to 90 [MPa], the all-solid electrolyte of this example was prepared in the same manner as in Example 1 described above. A lithium secondary battery was produced. In addition, when the positive electrode active material layer is formed using the composition of the positive electrode mixture (types and volume ratios of the positive electrode active material and the solid electrolyte), the positive electrode active material due to volume expansion of the positive electrode active material during battery charging When considering the maximum value of the internal pressure of the material layer, the permissible upper limit of the confining pressure at which cracks do not occur in the solid electrolyte was experimentally calculated and found to be 105 [MPa]. In addition, when the volume modulus of the solid electrolyte is increased from the positive electrode mixture composition described above, the permissible upper limit of the confining pressure at which cracks do not occur in the solid electrolyte gradually decreases. The bulk modulus of the solid electrolyte with the allowable upper limit of zero (0) was calculated to be 6.6 [GPa].

In the all-solid lithium secondary battery produced above, cracks do not occur in the solid electrolyte contained in the positive electrode active material layer even after the charge-discharge reaction proceeds. This is because the restraining pressure applied by the fastening member is 65 [MPa], which is smaller than the above-mentioned allowable upper limit value (105 [MPa]), and the volume expansion of the positive electrode active material due to charging and discharging of the battery. This is because the sum of the maximum value of the internal pressure of the positive electrode active material layer caused by the above-described constraint pressure is smaller than the yield stress of the solid electrolyte contained in the positive electrode active material layer.

<Comparative Example 2>
An all-solid lithium secondary battery of this comparative example was produced in the same manner as in Example 2 described above, except that the binding pressure of the fastening jig was set to 150 [MPa].

In the all-solid lithium secondary battery produced above, after the charge-discharge reaction proceeds, a large number of cracks occur in the solid electrolyte contained in the positive electrode active material layer. This is because the restraining pressure applied by the fastening member is set to 150 [MPa], which is larger than the allowable upper limit value (105 [MPa]) described above, and the volume expansion of the positive electrode active material due to charging and discharging of the battery. This is because the sum of the maximum value of the internal pressure of the positive electrode active material layer caused by the above and the above-described restraining pressure is larger than the yield stress of the solid electrolyte contained in the positive electrode active material layer.

FIG. 6 shows a plot of the relationship between the bulk elastic modulus and the confining pressure of the solid electrolytes in Example 2 and Comparative Example 2 described above.

As described above, with the configuration according to the present invention, it is possible to prevent cracks from occurring in the electrode active material or the solid electrolyte due to the volume expansion of the electrode active material while suppressing the decrease in energy density. can.

10a, 50, 100 stacked secondary battery,
11' negative electrode current collector,
11″ cathode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 solid electrolyte layer,
19 cell layer,
21, 57 power generation element,
25 negative electrode current collector (negative electrode tab),
27 positive collector plate (positive tab),
29, 52 laminate film,
58 positive tab,
59 negative tab,
200 metal plate,
300 volts,
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,
The sum of the maximum value of the internal pressure of the electrode active material layer due to the volume expansion of the electrode active material due to charging and discharging of the battery and the restraining pressure applied by the restraining member is the electrode active material or the solid electrolyte. secondary battery, which is smaller than the yield stress of 2. The secondary battery according to claim 1, wherein said solid electrolyte contained in said electrode active material layer contains an S element. The electrode active material layer is a positive electrode active material layer containing a positive electrode active material as the electrode active material, the positive electrode active material contains M1 element and O element, and the M1 element is Li, Mn, Ni, Co 3. The secondary battery according to claim 1, containing at least one element selected from the group consisting of , Cr, Fe and P. 3. The second electrode according to claim 1 or 2, wherein the electrode active material layer is a positive electrode active material layer containing a positive electrode active material as the electrode active material, and the positive electrode active material is a positive electrode active material containing an S element. next battery. The solid electrolyte contained in the electrode active material layer is Li ₆ PS ₅ X (where X is Cl, Br or I), Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S and Li The secondary battery according to any one of claims 1 to ₄ , selected from the group consisting of _3PS4 .

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