JP7395290B2 - Electrodes for solid state batteries and solid state batteries - Google Patents

Description

The present invention relates to a solid state battery including a solid electrolyte. The present invention particularly relates to an electrode structure applied to the positive electrode or negative electrode of the solid-state battery.

A lithium secondary battery is a secondary battery that consists of a lithium transition metal oxide such as lithium cobalt oxide as a positive electrode material, a graphite-based carbon material as a negative electrode material, and an organic electrolyte. It operates as a battery by moving lithium ions from the positive electrode to the negative electrode during charging and from the negative electrode to the positive electrode during discharging. They are widely used as batteries for mobile devices because the amount of electricity that can be extracted per unit of battery volume or weight (energy density) is significantly greater than that of other secondary batteries. On the other hand, since an organic electrolyte or a gel polymer is used, there are problems with fluidity, liquid leakage due to softening properties, and safety due to flammability, and there is a need to solidify the electrolyte.

As solid electrolyte materials, inorganic solid electrolyte materials are nonflammable and highly safe, and are being developed to realize all-solid-state lithium secondary batteries (hereinafter referred to as all-solid-state batteries). ).

It is known that lithium ion conductivity can be increased by mixing a solid electrolyte material and an electrode active material to increase the specific surface area of the microscopic interface between the solid electrolyte and the electrode active material. In Patent Document 1, a positive electrode including a positive electrode composite layer containing a positive electrode active material powder and a solid electrolyte powder, a solid electrolyte layer, and a negative electrode current collector are sequentially formed on both sides of a flat positive electrode current collector. A lithium secondary battery having stacked solid electrolytes is disclosed.

In addition, when an electrode active material containing lithium is charged and discharged, lithium ions are injected and released. At this time, the electrode active material layer expands and contracts in volume, and cracks occur in the electrode layer containing the electrode active material. , is known to be a factor that inhibits ion conduction. As a countermeasure against battery warping and performance deterioration due to such charging and discharging, it is known to provide an electrode active material layer with a predetermined gradient in the layer thickness direction. Patent Document 2 discloses an all-solid-state battery including a composite active material layer having a first gradient in which the concentration and porosity of an electrode active material increase from the solid electrolyte layer side to the current collector layer side. ing. The all-solid-state battery described in Patent Document 2 includes a composite active material having a second gradient in which the concentration of the solid electrolyte decreases from the solid electrolyte layer side to the current collector layer side so as to compensate for the first gradient. It has a material layer.

Japanese Patent Application Publication No. 2009-146657 Japanese Patent Application Publication No. 2012-104270

As inorganic solid electrolytes, sulfide-based solid electrolytes and oxide-based solid electrolytes are known. Solid electrolytes are superior to conventional liquid electrolytes (electrolytes) in terms of reliability and portability in that they are less susceptible to liquid leakage and the like. On the other hand, since inorganic solid electrolytes have lower flexibility than conventional electrolytes, it is difficult to form an interface with an active material related to carrier transport.

The electrodes for solid batteries described in Patent Documents 1 and 2 alleviate the volume change of the active material layer due to repeated charging and discharging on the side of the active material layer at the interface with the solid electrolyte layer, which has low flexibility. I was worried that I wouldn't be able to do it. In addition, in the electrode for a solid battery described in Patent Document 2, in order to form an active material layer that includes predetermined voids on the current collector layer side, the electrode is formed at the interface between the solid electrolyte and the electrode active material. There was a concern that carrier movement would be restricted due to the limited non-surface area.

The present invention is directed to a solid state battery for a solid state battery having an active material layer containing a solid electrolyte and an active material, to which a solid electrolyte with low flexibility can be applied, and in which a decrease in carrier transport ability due to charge/discharge cycles is improved. The purpose is to provide electrodes. Further, the present invention aims to provide a highly reliable solid state battery.

An electrode according to an embodiment of the present invention is an electrode for a solid-state battery in which a current collector layer and an active material layer containing an active material and a conductive additive that are partially in contact with the current collector layer are laminated. And,
The active material layer has a region exhibiting a concentration gradient in which the active material increases in the layer thickness direction toward the side in contact with the current collector layer, and the conductive additive decreases in the region in the layer thickness direction. The active material layer is characterized in that it further contains a solid electrolyte that exhibits a concentration gradient that increases in the region in the layer thickness direction .

According to the present invention, it is possible to provide an electrode for an all-solid-state battery that contains a conductive additive and an electrode active material that have improved performance deterioration due to charge/discharge cycles. Further, according to the present invention, it is possible to provide a highly reliable all-solid-state battery in which performance deterioration due to charge/discharge cycles is improved.

1 shows a laminated structure (a) of a positive electrode according to a first embodiment of the present invention, and (b) a volume fraction distribution of contained components in the layer thickness direction of a positive electrode active material layer. It shows the laminated structure of an all-solid-state battery according to a second embodiment of the present invention. 3 shows volume fraction distributions (a) to (c) of components contained in the positive electrode active material layers in the layer thickness direction according to the third to fifth embodiments of the present invention.

Below, preferred embodiments of the present invention will be described in detail using the drawings. The dimensions, materials, shapes, relative arrangements, etc. of the constituent members described in these embodiments are not intended to limit the scope of the present invention.

(First embodiment)
First, a positive electrode including a positive electrode active material layer 20 will be described as an electrode according to the first embodiment. FIGS. 1A and 1B are a cross-sectional diagram showing the positive electrode 30 according to the present embodiment, and a graph showing the volume fraction distribution of the contained components in the layer thickness direction 220 of the positive electrode active material layer 20, respectively. be.

The positive electrode 30 has a current collector layer 10, an active material layer 20 containing a positive electrode active material 120, and a conductive additive 170, as shown in FIG. 1(a). The active material layer 20 is sometimes referred to as a composite active material layer.

The current collector layer 10 is a conductor that conducts electrons between an external circuit (not shown) and an active material layer. The current collector layer 10 is in the form of a laminate of a self-supporting film of metal such as copper or aluminum, metal foil, or a resin base.

The active material layer 20 includes active material layers 20a, 20b, and 20c as sublayers in which the volume fractions of the positive electrode active material 120 and the conductive additive 170 are different from each other.

In the active material layers 20a to 20c, as shown in FIG. 1(b), the closer the sublayer is to the current collector 10, the higher the volume fraction of the positive electrode active material 120, and the lower the volume fraction of the conductive additive 170. It exhibits a low volume fraction profile in the stacking direction 200. In other words, the positive electrode 30 of this embodiment exhibits a concentration gradient having an inclination in the opposite direction between the positive electrode active material 120 and the conductive additive 170 in the stacking direction 200. The positive electrode active material layer 20 has a region in which the positive electrode active material 120 exhibits an increasing concentration gradient in the layer thickness direction 200 toward the side in contact with the current collector layer 10 . On the other hand, in other words, the conductive additive 170 exhibits a decreasing concentration gradient in such a region in the layer thickness direction 200.

The positive electrode active material 120 of this embodiment is LiCoO ₂ (lithium cobalt oxide: hereinafter sometimes abbreviated as LCO), and the conductive aid 170 is Li ₃ BO ₃ (lithium borate: hereinafter sometimes abbreviated as LBO). be. The positive electrode active material 120 (LCO) and the conductive support agent 170 (GC) of this embodiment have different particle size distributions and average particle diameters, and the average particle diameter of LCO is about 2 to 3 times larger than that of LBO.

The content ratio of the positive electrode active material 120 on the solid electrolyte layer 40 side of the active material layer 20 is relatively lower than that on the current collector 10 side, and lithium ions between the solid electrolyte layer 40 and the solid electrolyte 40 in the solid electrolyte layer 40 are relatively low. The movement in and out of the positive electrode active material 120 is localized, and the influence of the volume change of the positive electrode active material 120 increases. In the positive electrode 30 (electrode 30) according to the present embodiment, the conductive additive 170 is arranged on the solid electrolyte layer 40 side of the active material layer 20 so as to absorb the volume change of the positive electrode active material 120.

Further, as inorganic solid electrolytes, sulfide-based solid electrolytes and oxide-based solid electrolytes are known.

A sulfide-based solid electrolyte has a lithium ion conductivity about an order of magnitude higher than an oxide-based solid electrolyte, and is a solid with excellent plasticity, so a bond between the electrode and the solid electrolyte can be easily formed. However, there is a concern that sulfide-based solid electrolytes generate toxic hydrogen sulfide gas when exposed to the atmosphere, which increases manufacturing costs such as the need for a sealing structure for mounting, and reduces effective mounting density. There was a problem with the decline in

On the other hand, oxide-based solid electrolytes do not require a sealing structure due to their chemical stability, but are less flexible than sulfide-based electrolytes. For this reason, it is difficult to alleviate the effect of the volume change accompanying charging and discharging of the active material contained in the active material layer described above.

The positive electrode 30 according to the present embodiment includes the conductive additive 170 as a buffering agent that alleviates the effect of volume change on the side of the electrolyte layer 40 of the active material layer 20, so that such a solid electrolyte with low flexibility is used. It is also suitable for solid state batteries comprising an electrolyte layer comprising:

In this embodiment, the conductive additive 170 has a smaller particle size than the positive electrode active material 120 and is considered to ensure a higher density of contacts related to carrier transport to the positive electrode active material 120 on the current collector layer 10 side. In addition, it is thought that the conductive support agent 170 constitutes secondary particles whose particle size is smaller than that of the positive electrode active material 120, absorbs the volume change of the positive electrode active material 120 through deformation of the secondary particles, and ensures the effect of reducing stress. It will be done. In other words, the change in volume of the positive electrode active material 120 is absorbed by the primary displacement of the conductive support agent 170, thereby ensuring the effect of reducing stress.

The sublayers 20a, 20b, and 20c included in the positive electrode active material layer 20 can control the areal density of each layer by using a patterning method such as a printing plate, an electrophotographic method, an inkjet method, a mask method, etc. It is possible to form the volume density distribution of each layer.

In this embodiment, the concentration gradient between the positive electrode active material layers 20c and 20b located on the side far from the current collector layer 10 is different from the concentration gradient between the positive electrode active material layers 20b and 20a located on the side closer to the current collector layer 10. It exhibits a nonlinear concentration gradient that is larger than the gradient.

Examples of the positive electrode active material 120 include a composite metal oxide containing lithium, a chalcogen compound, and manganese dioxide. The composite metal oxide containing lithium is a metal oxide containing lithium and a transition metal, or a metal oxide in which a part of the transition metal in the metal oxide is replaced with a different element. Here, examples of the different elements include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. The number of different elements may be one or two or more. Among these, complex metal oxides containing lithium are preferred. Composite metal oxides containing lithium include Li _x CoO ₂ , Li _x NiO 2 , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y Mn _{1-y O z ,} Li _x Ni Examples include _1-y M _y O _z and Li _x Mn ₂ O ₄ . Further examples of the composite metal oxide containing lithium include Li _x Mn _2-y MyO ₄ , LiMPO ₄ , and Li ₂ MPO ₄ F. M in the formula is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B. x, y, z in the formula are 0<x≦1.2, 0<y<0.9, 2.0≦z≦2.3. Further examples of the composite metal oxide containing lithium include LiMeO ₂ (Me in the formula: Me=MxMyMz: Me and M are transition metals, x+y+z=1). Specific examples of composite metal oxides containing lithium include LiCoO ₂ (LCO: lithium cobalt oxide) and LiNi _0.5 Mn _1.5 O ₄ (LNMO: lithium nickel manganate). Further, specific examples of the composite metal oxide containing lithium include LiFePO ₄ (LFP: lithium iron phosphate) and Li ₃ V ₂ (PO ₄ ) ₃ (LVP: lithium vanadium phosphate). Moreover, the above-mentioned positive electrode material may contain a conductive additive. Examples of the conductive aid include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and fluorinated carbon powder. In addition, conductive aids include conductive fibers such as carbon fibers, carbon nanotubes, and metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide, and conductive metal oxides such as titanium oxide. Examples include organic conductive materials such as phenylene dielectrics.

It is preferable that the conductive support agent 170 has a lower Young's modulus than the positive electrode active material 120 in order to absorb changes in the volume of the positive electrode active material. In other words, it is preferable that the conductive support agent 170 has a lower elastic modulus than the positive electrode active material 120 in order to absorb volume changes of the positive electrode active material.

(Second embodiment)
This embodiment is an embodiment in which a solid battery 100 is constructed using the positive electrode 30 of the first embodiment. In other words, the positive electrode 30 of the first embodiment is applied to the positive electrode of the solid battery 100. The solid battery 100 includes a solid electrolyte layer 40 on the surface of the positive electrode active material layer 20 opposite to the current collector layer 10 side. The solid battery 100 includes a negative electrode 70 on the side opposite to the side where the solid electrolyte layer 40 is in contact with the positive electrode active material layer 20. The negative electrode 70 includes a negative electrode active material layer 50 on the side opposite to the side of the solid electrolyte layer 40 that is in contact with the positive electrode active material layer 20 . The negative electrode 70 includes a negative electrode current collector layer 60 on the side opposite to the side where the negative electrode active material layer 50 is in contact with the solid electrolyte layer 40 .

The solid electrolyte layer 40 includes an inorganic solid electrolyte. Examples of the solid electrolyte include oxide-based solid electrolytes, sulfide-based solid electrolytes, and complex hydride-based solid electrolytes. Oxide-based solid electrolytes include aluminum-substituted lithium germanium phosphate Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ and Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ . Examples include Nasicon type compounds. Examples of the oxide-based solid electrolyte include garnet-type compounds such as Li _6.25 La ₃ Zr ₂ Al _0.25 O ₁₂ or perovskite-type compounds such as Li _0.33 Li _0.55 TiO ₃ . Examples of the oxide-based solid electrolyte include lysicone-type compounds such as Li ₁₄ Zn(GeO ₄ ) ₄ and acid compounds such as Li ₃ PO ₄ , Li ₄ SiO ₄ , and Li ₃ BO ₃ . Specific examples of sulfide-based solid electrolytes include Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI -Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ and the like. Moreover, Li _6.75 La ₃ Zr _1.75 Nb _0.25 O ₁₂ (hereinafter referred to as LLZ) is also used as the solid electrolyte. Moreover, the solid electrolyte may be crystalline or amorphous, and may be glass ceramics. Note that descriptions such as Li ₂ SP ₂ S ₅ mean a sulfide-based solid electrolyte made using a raw material containing Li ₂ S and P ₂ S ₅ .

The positive electrode active material layer 20 may contain a solid electrolyte, but the composition may be the same or different from that of the solid electrolyte contained in the solid electrolyte layer 40. When the positive electrode active material layer 20 includes a solid electrolyte, it is preferable that the positive electrode active material layer 20 exhibits a lower Young's modulus (modulus of elasticity) than the solid electrolyte contained in the solid electrolyte layer 40 .

The negative electrode active material layer 50 can contain, for example, graphite, In, or the like as a negative electrode active material. Further, the current collector layer 60 for the negative electrode can be made of metal foil or metal film, similarly to the current collector layer 10 for the positive electrode.

The solid state battery 100 of the present embodiment reduces cracks due to volume changes of the positive electrode active material 120 on the current collector layer 10 side in the positive electrode active material layer 20 included in the positive electrode 30, and has a long life reliability. is high.

(Third embodiment)
In the positive electrode 30 of this embodiment, the volume fraction distribution in the stacking direction 200 of the positive electrode active material 120 and the conductive additive 170 contained in the positive electrode active material layer 20 is as shown in FIG. This is different from the positive electrode 30 of Form 1. In the positive electrode active material layer 20 of this embodiment, even in the positive electrode active material layer 20a closest to the current collector layer 10, the volume fraction of the positive electrode active material 120 (LCO) is lower than that of the conductive additive 170 (GC). The other points are the same as the positive electrode 30 of the first embodiment. In the solid battery using the positive electrode 30 of this embodiment, as in the first embodiment, it is possible to reduce the effects of cracks and the like due to changes in the volume of the positive electrode active material 120.

(Fourth embodiment)
In the positive electrode 30 of this embodiment, the volume fraction distribution in the stacking direction 200 of the positive electrode active material 120 and the conductive additive 170 contained in the positive electrode active material layer 20 is as shown in FIG. This is different from the positive electrode 30 of Form 1. The positive electrode active material layer 20 of this embodiment has the same volume fraction of the positive electrode active material 120 (LCO) in the two positive electrode active material layers 20a and 20b closer to the current collector layer 10, and a conductive additive. The positive electrode 30 of the first embodiment is the same as the positive electrode 30 of the first embodiment except that the volume fraction of 170 (GC) is also the same.

In the solid battery using the positive electrode 30 of this embodiment, as in the first embodiment, it is possible to reduce the effects of cracks and the like due to changes in the volume of the positive electrode active material 120.

(Fifth embodiment)
In the positive electrode 30 of this embodiment, the volume fraction distribution in the stacking direction 200 of the positive electrode active material 120 and the conductive additive 170 contained in the positive electrode active material layer 20 is as shown in FIG. This is different from the positive electrode 30 of Form 1. The positive electrode active material layer 20 of this embodiment contains lithium borate (LBO) as a solid electrolyte in each layer 20a to 20c, and the volume fraction of the solid electrolyte (LBO) increases as it approaches the current collector layer 10 side. It is declining. That is, the positive electrode active material layer 20 of this embodiment is the same as that of Embodiment 1, except that in the layer thickness direction 200, there is a region exhibiting a concentration gradient in which the solid electrolyte decreases as it approaches the solid electrolyte layer side. This is the same as the positive electrode 30.

In the solid battery using the positive electrode 30 of this embodiment, as in the first embodiment, it is possible to reduce the effects of cracks and the like due to changes in the volume of the positive electrode active material 120.

10 Current collector layer 20 Positive electrode active material layer (electrode active material layer)
30 Positive electrode (electrode)
120 Positive electrode active material (active material)
170 Conductive aid 200 Layer thickness direction

Claims (13)

An electrode applied to a solid-state battery in which a current collector layer and an active material layer containing an active material and a conductive additive partially in contact with the current collector layer are stacked,
The active material layer has a region exhibiting a concentration gradient in which the active material increases in the layer thickness direction toward the side in contact with the current collector layer, and the conductive additive decreases in the region in the layer thickness direction. The electrode is characterized in that the active material layer further contains a solid electrolyte that exhibits a concentration gradient that increases in the region in the layer thickness direction . The electrode according to claim 1, wherein the conductive additive has a lower Young's modulus than the active material. The electrode according to claim 1 or 2 , wherein the solid electrolyte is an inorganic substance containing an oxide or a sulfide. The electrode according to any one of claims 1 to 3 , wherein the solid electrolyte contains lithium. The electrode according to claim 4 , wherein the solid electrolyte includes at least one of lithium borate, aluminum-substituted lithium germanium phosphate, and LLZ. The electrode according to any one of claims 1 to 5, wherein the active material is a positive electrode active material containing lithium or a negative electrode active material containing lithium. The electrode according to claim 6 , wherein the positive electrode active material contains lithium cobalt oxide. The electrode according to any one of claims 1 to 7, wherein the conductive additive contains carbon black, carbon fiber, carbon nanotube, fluorinated carbon powder, metal powder, and metal fiber. The electrode according to any one of claims 1 to 8 ,
A solid-state battery comprising: a solid electrolyte layer in contact with the active material layer on a side opposite to the side in contact with the current collector layer. The solid battery according to claim 9 , wherein the solid electrolyte contained in the solid electrolyte layer and the solid electrolyte contained in the active material layer have different compositions. The solid battery according to claim 9 or 10 , wherein the solid electrolyte layer does not contain a positive electrode active material. The active material layer is a positive electrode active material layer containing a positive electrode active material,
The solid-state battery according to any one of claims 9 to 11 , further comprising a negative electrode active material layer in contact with the solid electrolyte layer on a side opposite to the positive electrode active material layer. The solid battery according to claim 12 , further comprising a negative electrode current collector layer in contact with the negative electrode active material layer on a side opposite to a side in contact with the solid electrolyte layer.

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