Patent Publication Number: US-2022231329-A1

Title: Coin-type all-solid-state battery and method of manufacturing the same

Description:
This application is based on and claims the benefit of priority from Japanese Patent Application No. 2021-006216, filed on 19 Jan. 2021, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a coin-type all-solid-state battery and a method of manufacturing the same. 
     Related Art 
     Conventionally, lithium ion secondary batteries have been widely used as secondary batteries having a high energy density. In the case of a solid-state battery where the electrolyte is solid, the battery has a cell structure in which a solid electrolyte is present between a positive electrode and a negative electrode. 
     In the case of a solid-state battery, sufficient adhesion is required between an electrode material mixture containing a positive electrode active material or a negative electrode active material and a solid electrolyte from the viewpoint of maintaining the ionic conductivity of lithium ions or the like. If the adhesion decreases due to repeated expansion and contraction during charging and discharging, ionic conductivity decreases. Therefore, the electrode material mixture and the solid electrolyte need to be constrained in a pressurized state by pressing or other means. 
     In the case of a coin-type all-solid-state battery, an electrode stack is sandwiched between a top metallic lid member and a bottom metallic receiving member, which serve as current collecting electrodes, and the stack is integrated by applying pressure from the top lid member side and the bottom receiving member side, to construct a coin-shaped all-solid-state battery. Accordingly, it is difficult to efficiently collect current while maintaining the above pressurized and constrained state. 
     In this regard, for example, Patent Document 1 discloses a coin-type all-solid-state battery in which conductive layers each including a porous metal are provided above and below an electrode stack to improve the adhesion between the conductive layers and the electrode stack.
     Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2005-056827   

     SUMMARY OF THE INVENTION 
     However, even in Patent Document 1, the bonding between the porous metal and the electrode stack is insufficient, and a more reliable and simple current collecting structure is required. 
     In response to the above issue, it is an object of the present invention to provide a current collecting structure capable of reliably collecting current while maintaining a pressurized and constrained state of a coin-type all-solid-state battery. 
     The inventors have found that the above issue can be solved by respectively disposing current collectors each including a metal porous body on the bonding faces of the electrode stack and the lid member (receiving member), making them face each other and pressure-bonding and integrating them. That is, the present invention provides the following. 
     (1) A first aspect of the present invention relates to a coin-type all-solid-state battery. The coin-type all-solid-state battery includes a solid electrolyte layer; a first electrode current collector of a positive electrode and a first electrode current collector of a negative electrode each including a metal porous body, the first electrode current collectors being respectively disposed on both sides of the solid electrolyte layer; a second electrode current collector of the positive electrode and a second electrode current collector of the negative electrode each including a metal porous body, the second electrode current collectors being respectively disposed on outer sides of the first electrode current collectors of the positive electrode and the negative electrode; and a lid member and a receiving member each capable of collecting current, the lid member and the receiving member being respectively disposed on outer sides of the second electrode current collectors of the positive electrode and the negative electrode. The first electrode current collector has a first face having an electrode material mixture filled region including an electrode material mixture that fills pores of the metal porous body, the first face being in contact with the solid electrolyte layer. The first electrode current collector has a second face having an electrode material mixture non-filled region not including the electrode material mixture. The electrode material mixture non-filled region of the first electrode current collector and the second electrode current collector are pressure-bonded. 
     According to the invention of the first aspect, the electrode material mixture non-filled region of the first electrode current collector and the second electrode current collector, which each include a metal porous body, are intertwined with each other and compression bonded by pressure bonding. In addition, the bonding is stabilized by the anchor effect between the surface irregularities of the electrode material mixture non-filled region of the first electrode current collector and the surface irregularities of the second electrode current collector. Therefore, when expansion and contraction repeatedly occur during charging and discharging, the elasticity of the metal porous bodies can provide a followability effect, thus suppressing a decrease in the current collecting effect. 
     (2) In a second aspect of the present invention according to the first aspect, a first of the second electrode current collectors and the lid member are bonded to each other by ultrasonic welding or welding, and a second of the second electrode current collectors and the receiving member are bonded to each other by ultrasonic welding or welding. 
     According to the invention of the second aspect, the second electrode current collectors can be respectively firmly bonded to the inner side of the lid member and the inner side of the receiving member, so that a decrease in the current collecting effect can be further suppressed. 
     (3) In a third aspect of the present invention according to the first or second aspect, bonding faces of the electrode material mixture non-filled region of the first electrode current collector and the second electrode current collector that are pressure-bonded, respectively include an engagement projection and an engagement recess that engage with each other. 
     According to the invention of the third aspect, engagement of the recess and the projection on the bonding faces facilitates positioning and prevents misalignment of the boding faces. 
     (4) A fourth aspect of the present invention relates to a method of manufacturing a coin-type all-solid-state battery. The method includes a first step of obtaining each of a first electrode current collector of a positive electrode and a first electrode current collector of a negative electrode by filling pores of a metal porous body with an electrode material mixture to form an electrode material mixture filled region on a first face of the metal porous body, and forming an electrode material mixture non-filled region not including the electrode material mixture on a second face of the metal porous body; a second step of obtaining an electrode stack by respectively bonding the first electrode current collector of the positive electrode and the first electrode current collector of the negative electrode to both sides of a solid electrolyte layer so that the electrode material mixture filled regions face each other; a third step of obtaining a current collector of the positive electrode and a current collector of the negative electrode by respectively bonding a lid member and a receiving member to first faces of second electrode current collectors each including another metal porous body; and a fourth step of respectively making the electrode material mixture non-filled regions of the first electrode current collectors after the second step and second faces of the second electrode current collectors after the third step face each other and pressure-bonding the electrode material mixture non-filled regions of the first electrode current collectors and the second faces of the second electrode current collectors from at least a side of the lid member or the receiving member to integrate them. 
     According to the invention of the manufacturing method of the fourth aspect, integration by pressure bonding is possible, which eliminates the need for other bonding means such as welding, thereby simplifying the manufacturing of coin-type all-solid-state batteries and improving productivity. 
     (5) In a fifth aspect of the present invention according to the fourth aspect, an engagement projection and an engagement recess that engage with each other are respectively formed on a surface of the electrode material mixture non-filled region in the first step and a second face of the second electrode current collector in the third step. In the fourth step, the pressure bonding is performed in a state in which the engagement recess and the engagement projection are engaged with each other. 
     According to the invention of the fifth aspect, the engagement of the recess and the projection on the bonding faces prevents misalignment of the bonding faces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional schematic diagram showing an embodiment of a coin-type all-solid-state battery of the present invention; 
         FIG. 2  is an exploded view before pressure bonding in  FIG. 1 ; and 
         FIG. 3  is an exploded view of a modification of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will now be described with reference to the drawings. The present invention is not limited to the following embodiments. In the following embodiments, a solid-state lithium ion battery will be used as an example, but the present invention can be applied to batteries other than lithium ion batteries. 
     First Embodiment 
     &lt;Overall Structure of Coin-Type All-Solid-State Battery&gt; 
     As shown in  FIG. 1 , a coin-type all-solid-state battery  100  according to this embodiment is a circular planar body as a whole in plan view. An electrode stack  50  is disposed between a lid member  60  and a receiving member  70 , which also serve as outer packaging containers and current collecting electrodes. The lid member  60  and the receiving member  70  are concave-shaped to each other by a caulking process after pressure bonding, and are fitted to each other and integrated. An insulator  80  is disposed in the gap therebetween. In this state, the lid member  60  and the receiving member  70  respectively constitute the external electrodes of a positive electrode and a negative electrode of the battery. 
     In the electrode stack  50 , a first electrode current collector  10  that forms the positive electrode, a solid electrolyte layer  30 , and a first electrode current collector  20  that forms the negative electrode are arranged in a stack in this sequence. The first electrode current collector  10  of the positive electrode is entirely composed of a metal porous body, and has a bonding face to the solid electrolyte layer  30  including a metal porous body. The bonding face has an electrode material fixture filled region  11 , which is filled with a positive electrode material mixture to form a positive electrode material mixture layer. The face opposite to the bonding face constitutes an electrode material mixture non-filled region  12  consisting only of the metal porous body. Similarly, the first electrode current collector  20  of the negative electrode is entirely composed of a metal porous body, and includes an electrode material fixture filled region  21 , which is filled with a negative electrode material mixture to form a negative electrode material mixture layer, and an electrode material mixture non-filled region  22  consisting only of the metal porous body. 
     In other words, the electrode stack  50  has a layer structure of the electrode material mixture non-filled region  12  of the positive electrode, the electrode material mixture filled region  11  of the positive electrode, the solid electrolyte layer  30 , the electrode material mixture filled region  21  of the negative electrode, and the electrode material mixture non-filled region  22  of the negative electrode. 
     A second electrode current collector  15  of the positive electrode is bonded to the inner side of the lid member  60 . A second electrode current collector  25  of the negative electrode is bonded to the inner side of the receiving member  70 . The electrode material mixture non-filled region  12  of the positive electrode and the second electrode current collector  15  of the positive electrode are compression bonded at bonding faces  40 . The electrode material mixture non-filled region  22  of the negative electrode and the second electrode current collector  25  of the negative electrode are compression bonded at bonding faces  40 . 
     The respective components will be described below. 
     &lt;Positive Electrode and Negative Electrode&gt; 
     In this embodiment, the first electrode current collectors  10  and  20  each constitutes a current collector including a metal porous body having pores (communicating pores) that are continuous with each other. Pores of each of the current collectors are filled with an electrode material mixture (positive electrode material mixture or negative electrode material mixture) including an electrode active material. 
     (Current Collector) 
     The current collector includes a metal porous body having pores that are continuous with each other. The porosity is preferably 50% or more and 99% or less. Having pores that are continuous with each other allows the pores to be filled with a positive electrode material mixture or a negative electrode material mixture containing an electrode active material, thereby increasing the amount of the electrode active material per unit area of the electrode layer. The form of the metal porous body is not limited as long as it has pores that are continuous with each other. Examples of the form of the metal porous body include a foam metal having pores by foaming, a metal mesh, an expanded metal, a punching metal, and a metal nonwoven fabric. 
     The metal used in the metal porous body is not limited as long as it has electric conductivity. Examples thereof include nickel, aluminum, stainless steel, titanium, copper, and silver. Among these, as the current collector constituting the positive electrode, a foamed aluminum, foamed nickel, and foamed stainless steel are preferable. As the current collector constituting the negative electrode, a foamed copper and foamed stainless steel are preferable. 
     By using the current collector including the metal porous body, the amount of the active material per unit area of the electrode can be increased, and as a result, the volumetric energy density of the lithium ion secondary battery can be improved. In addition, since the positive electrode material mixture and the negative electrode material mixture are easily fixed, it is not necessary to thicken a coating slurry for forming the electrode material mixture layer when the electrode material mixture layer is thickened, unlike a conventional electrode including a metal foil as a current collector. Accordingly, it is possible to reduce a binder such as an organic polymer compound that has been necessary for thickening. Therefore, the capacity per unit area of the electrode can be increased, and a higher capacity of the lithium ion secondary battery can be achieved. 
     (Electrode Material Mixture) 
     The positive electrode material mixture and the negative electrode material mixture are respectively disposed in the pores formed within the current collectors. The positive electrode material mixture and the negative electrode material mixture respectively contain a positive electrode active material and a negative electrode active material as an essential component. 
     (Electrode Active Material) 
     The positive electrode active material is not limited as long as it can occlude and release lithium ions. Examples thereof include LiCoO 2 , Li(Ni 5/10 Co 2/10 Mn 3/10 )O 2 , Li(Ni 6/10 Co 2/10 Mn 2/10 )O 2 , Li(Ni 8/10 Co 1/10 Mn 1/10 )O 2 , Li(Ni 0.8 Co 0.15 Al 0.09 )O 2 , Li(Ni 1/6 Co 4/6 Mn 1/6 )O 2 , Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 , Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 , LiCoO 4 , LiMn 2 O 4 , LiNiO 2 , LiFePO 4 , lithium sulfide, and sulfur. 
     The negative electrode active material is not limited as long as it can occlude and release lithium ions. Examples thereof include metallic lithium, lithium material mixtures, metal oxides, metal sulfides, metal nitrides, Si, SiO, and carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon. 
     (Other Components) 
     The electrode material mixture may optionally include components other than an electrode active material and ionic conductive particles. The other components are not limited, and can be any components that can be used in fabricating a lithium ion secondary battery. Examples thereof include a conductivity aid and a binder. The conductivity aid of the positive electrode is, for example, acetylene black, and the binder of the positive electrode is, for example, polyvinylidene fluoride. Examples of the binder of the negative electrode include sodium carboxyl methyl cellulose, styrene-butadiene rubber, and sodium polyacrylate. 
     &lt;Solid Electrolyte Layer&gt; 
     The solid electrolyte constituting the solid electrolyte layer  30  is not limited, and is, for example, a sulfide solid electrolyte material, an oxide solid electrolyte material, a nitride solid electrolyte material, or a halide solid electrolyte material. Examples of the sulfide solid electrolyte material include LPS halogens (Cl, Br, and I), Li 2 S—P 2 S 5 , and Li 2 S—P 2 S 5 —LiI for lithium ion batteries. The above-described “Li 2 S—P 2 S 5 ” refers to a sulfide solid electrolyte material including a raw material composition containing Li 2 S and P 2 S 5 , and the same applies to the “Li 2 S—P 2 S 5 —LiI”. Examples of the oxide solid electrolyte material include NASICON-type oxides, garnet-type oxides, and perovskite-type oxides for lithium ion batteries. Examples of the NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li 1.5 Al 0.5 Ti 1.5 (PO 4 ) 3 ). Examples of the garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., Li 7 La 3 Zr 2 O 12 ). Examples of the perovskite-type oxides include oxides containing Li, La, Ti, and O (e.g., LiLaTiO 3 ). 
     &lt;Method of Manufacturing Coin-Type All-Solid-State Battery&gt; 
     The coin-type all-solid-state battery  100  will be described in detail in line with the manufacturing method with reference to the exploded view shown in  FIG. 2 .  FIG. 2  is an exploded view of an example of the manufacturing method of the present invention. 
     (First Step) 
     A first step is a step of obtaining a first electrode current collector  10   a  of the positive electrode and a first electrode current collector  20   a  of the negative electrode. Specifically, on first faces of metal porous bodies, pores are filled with electrode material mixtures to form electrode material mixture filled regions  11  and  21 . On second faces, electrode material mixture non-filled regions  12   a  and  22   a  not including the electrode material mixtures are formed. Thus, the first electrode current collector  10   a  of the positive electrode and the first electrode current collector  20   a  of the negative electrode are obtained. 
     The first electrode current collectors  10   a  and  20   a  are each obtained by filling the pores only on the first face of the metal porous body having pores that are continuous with each other as a current collector with the electrode material mixture. First, an electrode active material and, if necessary, a binder and a conductivity aid, are uniformly mixed by a conventionally known method, and thus an electrode material mixture composition adjusted to a predetermined viscosity, preferably in the form of a paste, is obtained. 
     Subsequently, pores of a metal porous body, which is a current collector, are filled with the above electrode material mixture composition as an electrode material mixture. The method of filling the current collector with the electrode material mixture is not limited, and is, for example, a method of filling the pores of the current collector with a slurry containing the electrode material mixture by applying pressure using a plunger-type die coater. As an alternative, the interior of the metal porous body may be impregnated with an ion conductor layer by a dipping method. At this time, by filling the electrode material mixtures only from the first faces of the metal porous bodies, it is possible to obtain the first electrode current collectors each including the electrode material mixture filled region  11  ( 21 ) and the electrode material mixture non-filled region  12   a  ( 22   a ). 
     (Second Step) 
     A second step is a step of obtaining an electrode stack  50   a . The first electrode current collectors  10   a  and  20   a  are respectively attached to both sides of the solid electrolyte layer  30  so that the electrode material mixture filled regions  11  and  21  face each other, and thereby the electrode stack  50   a  is formed. 
     (Third Step) 
     In a third step, the lid member  60  is stacked on a first face of a second electrode current collector  15   a  including a metal porous body, to obtain a positive electrode current collector. Similarly, the receiving member  70  is stacked on a first face of a second electrode current collector  25   a  including a metal porous body, to obtain a negative electrode current collector. The stacking is preferably performed by bonding under pressure, such as ultrasonic welding or resistance welding. As a result, each of the metal porous bodies is compressed by pressing at the time of bonding, and is bonded to the lid member  60  or the receiving member  70  in a high-density state, which is expected to improve the strength of the bonding portions. At this time, recesses  15   c  and  25   c  are respectively formed on the second electrode current collectors  15   a  and  25   a  by pressing at the time of bonding. 
     (Fourth Step) 
     Finally, the electrode material mixture non-filled region  12   a  of the first electrode current collector after the second step and the second electrode current collector  15   a  after the third step are disposed to face each other to constitute the positive electrode side. Similarly, the electrode material mixture non-filled region  22   a  of the first electrode current collector after the second step and the second electrode current collector  25   a  after the third step are disposed to face each other to constitute the negative electrode side. In this state, they are bonded and integrated by applying pressure from above and below, i.e., from the lid member  60  and the receiving member  70  sides. 
     The pressure bonding can be performed by a conventionally known pressing process. At this time, when the lid member  60  and the receiving member  70  are integrated by the caulking process, the insulator  80  fills the space between the lid member  60  and the receiving member  70 . 
     By the pressurization process, the electrode material mixture non-filled region  12   a  ( 22   a ) of the first electrode current collector and the part of the second electrode current collector  15   a  ( 25   a ) other than the recess  15   c  ( 25   c ) are compressed in a state in which their metal porous bodies are intertwined with each other to reduce their thickness. As shown in  FIG. 1 , the electrode material mixture non-filled region  12  ( 22 ) of the first electrode current collector and the second electrode current collector  15  ( 25 ) are compression bonded with the bonding faces  40  interposed therebetween. In this way, by pressure-bonding the metal porous bodies to form a current collector, even when expansion and contraction repeatedly occur during charging and discharging, as is the case with lithium ion batteries, the elasticity of the metal porous bodies can provide a followability effect, thus suppressing a decrease in the current collecting effect and extending the life span of the current collector. 
     [Modification] 
       FIG. 3  shows a modification of  FIG. 2 . In this embodiment, a projection  12   b  is formed on a surface of an electrode material mixture non-filled region  12   a , and a recess  15   b  is formed on a surface of a second electrode current collector  15   a . The surfaces form bonding faces  40  during pressure-bonding. This is a difference from  FIG. 2 . The recess  15   b  and the projection  12   b  face each other to engage with each other. The same applies to a projection  22   b  formed on a surface of an electrode material mixture non-filled region  22   a  and a recess  25   b  formed on a surface of a second electrode current collector  25   a , of a negative electrode side. 
     In this state, pressure bonding is performed in the fourth step so that the recess  15   b  ( 25   b ) and the projection  12   b  ( 22   b ) engage with each other, which facilitates alignment of the bonding faces and prevents misalignment of the bonding faces. The shapes, positions, and numbers of recess(es) and projection(s) that engage with each other are not limited. 
     Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         
           
               10  first electrode current collector (positive electrode) 
               10   a  first electrode current collector (positive electrode) before pressure bonding 
               11  electrode material mixture filled region (positive electrode material mixture layer) 
               12  electrode material mixture non-filled region (positive electrode) 
               12   a  electrode material mixture non-filled region (positive electrode) before pressure bonding 
               12   b  projection 
               15  second electrode current collector (positive electrode) 
               15   a  second electrode current collector (positive electrode) before pressure bonding 
               15   b  recess 
               15   c  recess 
               20  first electrode current collector (negative electrode) 
               20   a  first electrode current collector (negative electrode) before pressure bonding 
               21  electrode material mixture filled region (negative electrode material mixture layer) 
               22  electrode material mixture non-filled region (negative electrode) 
               22   a  electrode material mixture non-filled region (negative electrode) before pressure bonding 
               22   b  projection 
               25  second electrode current collector (negative electrode) 
               25   a  second electrode current collector (negative electrode) before pressure bonding 
               25   b  recess 
               25   c  recess 
               30  solid electrolyte layer 
               40  bonding face 
               50  electrode stack 
               50   a  electrode stack before pressure bonding 
               60  lid member 
               70  receiving member 
               80  insulator 
               100  coin-type all-solid-state battery