Patent Publication Number: US-2020303780-A1

Title: Solid-state battery and method for manufacturing the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of International application No. PCT/JP2019/006941, filed Feb. 25, 2019, which claims priority to Japanese Patent Application No. 2018-037225, filed Mar. 2, 2018, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a solid-state battery and a method for manufacturing the same. 
     BACKGROUND OF THE INVENTION 
     In the related art, a solid-state battery that does not use an electrolytic solution is known (for example, Patent Document 1). Since the solid-state battery does not use the electrolytic solution, there are advantages that the solid-state battery can be used in a high-temperature atmosphere and has excellent safety. 
     In certain configurations, for example, a voltage higher than a voltage determined by a potential difference between a positive electrode and a negative electrode may be required depending on a type of an electronic device. In this case, when the solid-state battery with a fixed output voltage is used, it is necessary to prepare a plurality of solid-state batteries and connect these solid-state batteries in series. When the plurality of solid-state batteries are used, there is a problem that a large space is required as a mounting space for the solid-state batteries in addition to complexity of the mounting of the solid-state batteries. 
     Because the solid-state battery according to the present embodiment is connected in series and includes first and second elements each having the external electrode connected to the positive electrode and the external electrode connected to the negative electrode, the solid-state battery has the output voltage that is twice or more the voltage obtained from a single element. 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2015-220105 
    
    
     
       SUMMARY OF THE INVENTION 
       A main object of the present invention is to provide a solid-state battery having a high voltage. 
       A solid-state battery according to one aspect of the present invention includes a battery body, a first external electrode, a second external electrode, a third external electrode, and a fourth external electrode. The battery body includes a plurality of adjacent elements. A first element includes a first positive electrode, a first negative electrode, and a first solid electrolyte layer. The first positive electrode is drawn out to a first surface of the battery body. The first negative electrode faces the first positive electrode and is drawn out to a second surface of the battery body. The first solid electrolyte is between the first positive electrode and the first negative electrode. The second element includes a second positive electrode, a second negative electrode, and a second solid electrolyte layer. The second positive electrode is drawn out to the second surface. The second negative electrode faces the second positive electrode and is drawn out to first surface. The second solid electrolyte layer is between the second positive electrode and the second negative electrode. The first external electrode is provided on the first surface and is electrically connected to the first positive electrode. The second external electrode is provided on the second surface and is electrically connected to the first negative electrode. The third external electrode is provided on the second surface and is electrically connected to the second positive electrode. The fourth external electrode is provided on the first surface and is electrically connected to the second negative electrode. The first external electrode and the fourth external electrode or the second external electrode and the third external electrode are integral so as to connect the first element and the second element in series. 
       BRIEF EXPLANATION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a solid-state battery according to a first embodiment. 
         FIG. 2  is a schematic sectional view taken along line II-II of  FIG. 1 . 
         FIG. 3  is a schematic sectional view taken along line III-III of  FIG. 1 . 
         FIG. 4  is a schematic sectional view taken along line IV-IV of  FIGS. 2 and 3 . 
         FIG. 5  is a schematic sectional view taken along line V-V of  FIGS. 2 and 3 . 
         FIG. 6  is a schematic circuit diagram of the solid-state battery according to the first embodiment. 
         FIG. 7  is a schematic circuit diagram of a solid-state battery according to a second embodiment. 
         FIG. 8  is a schematic plan view of a part of a positive electrode green sheet. 
         FIG. 9  is a schematic plan view of a part of a negative electrode green sheet. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiment is merely an example. The present invention is not at all limited to the following embodiment. 
     In the drawings to be referred to in the embodiment, members having substantially the same function are referred to by the same reference symbols. The drawings to be referred to in the embodiment are schematically described. A ratio of dimensions of objects drawn in the drawings may be different from a ratio of dimensions of actual objects. The ratio of the dimensions of the objects may differ between the drawings. A specific ratio of dimensions of the objects needs to be determined in consideration of the following description. 
     First Embodiment 
       FIG. 1  is a schematic perspective view of a solid-state battery according to a first embodiment.  FIG. 2  is a schematic sectional view taken along line II-II of  FIG. 1 .  FIG. 3  is a schematic sectional view taken along line III-III of  FIG. 1 .  FIG. 4  is a schematic sectional view taken along line IV-IV of  FIGS. 2 and 3 .  FIG. 5  is a schematic sectional view taken along line V-V of  FIGS. 2 and 3 .  FIG. 6  is a schematic circuit diagram of the solid-state battery according to the first embodiment. 
     A solid-state battery  1  illustrated in  FIG. 1  is a battery in which all constituent elements are solid by using a solid electrolyte as an electrolyte and not using a liquid electrolytic solution. In the present embodiment, specifically, an example in which the solid-state battery  1  is a solid-state lithium-ion secondary battery will be described. However, the solid-state battery according to the present invention may be a solid-state battery other than the lithium-ion secondary battery. 
     As illustrated in  FIGS. 1 to 5 , the solid-state battery  1  includes a battery body  10 . A shape of the battery body  10  is not particularly limited. In the present embodiment, the battery body  10  has specifically a rectangular parallelepiped shape. The “rectangular parallelepiped shape” includes a rectangular parallelepiped shape of which corners and ridges are chamfered or rounded. 
     The battery body  10  includes first and second main surfaces  10   a  and  10   b , and first to fourth side surfaces  10   c  to  10   f . The first and second main surfaces  10   a  and  10   b  extend along an x-axis direction and a y-axis direction, respectively. The first and second side surfaces  10   c  and  10   d  extend along the y-axis direction and a z-axis direction, respectively. The third and fourth side surfaces  10   e  and  10   f  extend along the x-axis direction and the z-axis direction, respectively. 
     The battery body  10  includes a plurality of elements. Here, the “element” includes a positive electrode, a negative electrode, and a solid electrolyte layer provided between the positive electrode and the negative electrode, and denotes a chargeable and dischargeable electric storage element. 
     In the present embodiment, specifically, the battery body  10  includes a first element E 1  and a second element E 2  as illustrated mainly in  FIG. 6 . The second element E 2  is adjacent to the first element E 1  in the y-axis direction. 
     As illustrated in  FIG. 2 , the first element E 1  has a plurality of first positive electrodes  11   a  and a plurality of first negative electrodes  12   a . The first positive electrodes  11   a  and the first negative electrodes  12   a  extend along the x-axis direction and the y-axis direction, respectively. Thus, the first positive electrodes  11   a  and the first negative electrodes  12   a  are parallel to the first and second main surfaces  10   a  and  10   b , respectively. The plurality of first positive electrodes  11   a  and the plurality of first negative electrodes  12   a  are alternately provided at intervals in the z-axis direction. The first positive electrode  11   a  and the first negative electrode  12   a  which are adjacent to each other in the z-axis direction (laminating direction) face each other with a first solid electrolyte layer  13   a  interposed therebetween. 
     A size of the positive electrode  11   a  and a size of the negative electrode  11   b  may be equal or different. 
     Each of the plurality of first positive electrodes  11   a  are drawn out to the first side surface  10   c , but are not drawn out to the second side surface  10   d . The plurality of first positive electrodes  11   a  are electrically connected to a first external electrode (first positive electrode terminal electrode)  14   a  provided on the first side surface  10   c.    
     Each of the plurality of first negative electrodes  12   a  are drawn out to the second side surface  10   d , but are not drawn out to the first side surface  10   c . The plurality of first negative electrodes  12   a  are electrically connected to a second external electrode (first negative electrode terminal electrode)  15   a  provided on the second side surface  10   d.    
     As illustrated in  FIG. 3 , the second element E 2  includes a plurality of second positive electrodes lib and a plurality of second negative electrodes  12   b . The second positive electrodes lib and the second negative electrodes  12   b  extend along the x-axis direction and the y-axis direction, respectively. Thus, the second positive electrodes lib and the second negative electrodes  12   b  are parallel to the first and second main surfaces  10   a  and  10   b , respectively. The plurality of second positive electrodes  11   b  and the plurality of second negative electrodes  12   b  are alternately provided at intervals in the z-axis direction. The second positive electrode  11   b  and the second negative electrode  12   b  which are adjacent to each other in the z-axis direction (laminating direction) face each other with a second solid electrolyte layer  13   b  interposed therebetween. 
     Each of the plurality of second positive electrodes  11   b  are drawn out to the second side surface  10   d , but are not drawn out to the first side surface  10   c . The plurality of second positive electrodes  11   b  are electrically connected to a third external electrode (second positive electrode terminal electrode)  14   b  provided on the second side surface  10   d.    
     Each of the plurality of second negative electrodes  12   b  are drawn out to the first side surface  10   c , but are not drawn out to the second side surface  10   d . The plurality of second negative electrodes  12   b  are electrically connected to a fourth external electrode (second negative electrode terminal electrode)  15   b  provided on the first side surface  10   c.    
     As illustrated in  FIGS. 1, 4, 5, and 6 , in the solid-state battery  1 , the second external electrode (first negative electrode terminal electrode)  15   a  and the third external electrode (second positive electrode terminal electrode)  14   b  are integrally provided. Thus, the first element E 1  and the second element E 2  are connected in series. Thus, in a case where a voltage of the first element E 1  is V 1  and a voltage of the second element E 2  is V 2 , the solid-state battery  1  has three kinds of output voltages V 1 , V 2 , and V 1 +V 2 . In other words, a power of three kinds of voltages of V 1 , V 2 , and V 1 +V 2  can be output from the solid-state battery  1 . Specifically, the output voltage V 1  can be obtained by using the first external electrode  14   a  and the second external electrode  15   a . The output voltage V 2  can be obtained by using the third external electrode  14   b  and the fourth external electrode  15   b . The output voltage V 1 +V 2  can be obtained by using the first external electrode  14   a  and the fourth external electrode  15   b . Thus, the solid-state battery  1  can be used as a power source of the voltage V 1 , the voltage V 2 , and the voltage V 1 +V 2 . It is possible to drive an electronic device that requires a power of at least two kinds of the voltage V 1 , the voltage V 2 , and the voltage V 1 +V 2  by one solid-state battery  1 . Accordingly, a mounting area can be smaller in a case where the solid-state battery  1  is used than in a case where a plurality of solid-state batteries having different output voltages is used. 
     It has been described in the present embodiment that the first element E 1  and the second elements E 2  are connected in series by integrally connecting the second external electrode (first negative electrode terminal electrode)  15   a  and the third external electrode (second positive electrode terminal electrode)  14   b . However, in the present invention, a form of the external electrode is not particularly limited as long as the first element E 1  and the second element E 2  are connected in series. For example, the first external electrode (first positive electrode terminal electrode)  14   a  and the fourth external electrode (second negative electrode terminal electrode)  15   b  may be integrally provided, and the second and third external electrodes  15   a  and  14   b  may be provided separately. 
     An aspect in which the solid-state battery  1  is mounted on a mounting substrate is not particularly limited. For example, the solid-state battery  1  may be mounted such that the first side surface  10   c  faces the mounting substrate side. The solid-state battery  1  may be mounted such that the first or second main surface  10   a  or  10   b  faces the mounting substrate side. 
     It has been described in the present embodiment that the solid-state battery  1  includes two elements of the first element E 1  and the second element E 2 . However, the present invention is not limited to this configuration. 
     For example, the solid-state battery according to the present invention may include three or more elements connected in series by external electrodes. As the number of elements included in the solid-state battery becomes larger, the number of kinds of voltages that can be output becomes larger. 
     Specifically, for example, in a solid-state battery  1   a  according to a second embodiment illustrated in  FIG. 7 , a first element E 1 , a second element E 2 , and a third element E 3  are connected in series by external electrodes in this order. Thus, from the solid-state battery  1   a , a power of six kinds of voltages V 1 , V 2 , V 3 , V 1 +V 2 , V 2 +V 3 , and V 1 +V 2 +V 3  can be output. 
     (Constituent Material) 
     Materials of a positive electrode, a negative electrode, an external electrode, and a solid electrolyte layer constituting each of the elements E 1  and E 2  are not particularly limited. 
     For example, the positive electrode may be composed of a positive electrode active material layer, or may be composed of a positive electrode current collector layer and a positive electrode active material layer provided on the positive electrode current collector layer. 
     The positive electrode current collector layer contains a conductive material such as a carbon material or a metal material. Specific examples of the carbon material preferably used include, for example, graphite and carbon nanotubes. Specific examples of the metal material preferably used include, for example, Cu, Mg, Ti, Fe, Co, Ni, Zn, Al, Ge, In, Au, Pt, Pd, and alloys including these metal materials. The positive electrode current collector layer may further contain a binder and a solid electrolyte in addition to the conductive material. 
     The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material preferably used include lithium transition metal composite oxides and lithium transition metal phosphate compounds. Specific examples of the lithium transition metal composite oxide include LiCoO 2 , LiNiO 2 , LiVO 2 , LiCrO 2 , and LiMn 2 O 4 . Specific examples of the lithium transition metal phosphate compound include LiFePO 4  and LiCoPO 4 . The positive electrode active material layer may further contain a binder, a conductive material, and a solid electrolyte in addition to the positive electrode active material. 
     For example, the negative electrode may be composed of a negative electrode active material layer, or may be composed of a negative electrode current collector layer and a negative electrode active material layer formed on the negative electrode current collector layer. 
     The negative electrode current collector layer contains a conductive material such as a carbon material or a metal material. Examples of the carbon material and the metal material preferably used for the negative electrode current collector layer include the same carbon materials and metal materials preferably used for the positive electrode current collector layer described above. The negative electrode current collector layer may further contain a binder and a solid electrolyte in addition to the conductive material. 
     The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material preferably used include a carbon material, a metal material, a semimetal material, a lithium transition metal composite oxide, and lithium metal. Specific examples of the carbon material preferably used as the negative electrode active material include graphite, graphitizing carbon, non-graphitizing carbon, graphite, mesocarbon microbead (MCMB), and highly oriented graphite (HOPG). Specific examples of the metal material and the semimetal material preferably used as the negative electrode active material include Si, Sn, SiB 4 , TiSi 2 , SiC, Si 3 N 4 , SiOv (0&lt;v≤2), LiSiO, SnO w  (0&lt;w≤2), SnSiO 3 , LiSnO, and Mg 2 Sn. Specific examples of the lithium transition metal composite oxide preferably used as the negative electrode active material include Li 4 Ti 5 O 12 . The negative electrode active material layer may further contain a binder, a conductive material, and a solid electrolyte in addition to the negative electrode active material. 
     The solid electrolyte layer contains a solid electrolyte. Specific examples of the solid electrolyte preferably used include sulfides such as Li 2 S—P 2 S 5 , Li 2 S—SiS 2 —Li 3 PO 4 , Li 7 P 3 S 11 , Li 3.25 Ge 0.25 P 0.75 S, and Li 10 GeP 2 S 12 , oxides such as Li 7 La 3 Zr 2 O 12 , Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 , Li 6 BaLa 2 Ta 2 O 12 , Li 1+x Al x Ti 2−x (PO 4 ) 3 , and La 2/3−x Li 3x TiO 3 , and polymer materials such as polyethylene oxide (PEO). The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. 
     The external electrode contains a conductive material such as a metal material. Examples of the metal material preferably used for the external electrode include Ag, Au, Pt, Al, Cu, Sn, Ni, and alloys containing these metals. The external electrode may further contain a binder and a solid electrolyte in addition to the conductive material. 
     (Method for Manufacturing Solid-State Battery  1 ) 
     Next, an example of a method for manufacturing the solid-state battery  1  according to the first embodiment will be described. 
     First, green sheets  31   a  and  31   b  for forming the solid electrolyte layers  13   a  and  13   b  are prepared (see  FIGS. 8 and 9 ). The green sheets  31   a  and  31   b  can be prepared, for example, by the following procedure. First, a slurry is prepared by mixing a solid electrolyte with an organic binder, a solvent, and an additive. Subsequently, the green sheets  31   a  and  31   b  can be manufactured by applying the slurry onto a resin sheet, forming the slurry into a sheet shape, and drying the slurry. 
     Subsequently, as illustrated in  FIG. 8 , a positive electrode green sheet  30   a  is prepared by forming a plurality of positive electrode conductive paste layers  32   a  for forming the positive electrodes  11   a  and  11   b  in a matrix on the green sheet  31   a . In the present embodiment, an example in which two positive electrode conductive paste layers  32   a   1  for forming the positive electrode  11   a  are continuously formed in the x-axis direction, and two conductive paste layers  32   a   2  for forming the positive electrode  11   b  are continuously formed in the x-axis direction will be described below. Specifically, in the present embodiment, two positive electrode conductive paste layers  32   a   1  are formed integrally and two positive electrode conductive paste layers  32   a   2  formed integrally are formed in a zigzag manner so as to be shifted by a half period in the y-axis direction. 
     More specifically, such forming is as follows: Two first positive electrodes  11   a  are formed by the positive electrode conductive paste layers  32   a   1  (first positive electrode  11   a ×2), and two second positive electrodes  11   b  are formed by the positive electrode conductive paste layers  32   a   2  (second positive electrode  11   b ×2). The positive electrode conductive paste layers  32   a  are arranged at a predetermined pitch P along the x direction. A first group G 1  indicating a group of the positive electrode conductive paste layers  32   a  arranged in the x direction is arranged so as to be shifted by a half of the pitch P along the x direction with respect to the adjacent first group G 1 . 
     Similarly, as illustrated in  FIG. 9 , a negative electrode green sheet  30   b  is prepared by forming a plurality of negative electrode conductive paste layers  32   b  for forming the negative electrodes  12   a  and  12   b  in a matrix on the green sheet  31   b . In the present embodiment, an example in which two negative electrode conductive paste layers  32   b   1  for forming the negative electrode  12   a  are continuously formed in the x-axis direction, and negative electrode conductive paste layers  32   b   2  for forming the negative electrode  12   b  are continuously formed in the x-axis direction will be described. Specifically, in the present embodiment, the two negative electrode conductive paste layers  32   b   1  formed integrally and the two negative electrode conductive paste layers  32   b   2  formed integrally are formed in a zigzag manner so as to be shifted by a half period in the y-axis direction. 
     More specifically, such forming is as follows: Two first negative electrodes  12   a  are formed by the negative electrode conductive paste layers  32   b   1  (first negative electrode  12   a ×2), and two second negative electrodes  12   b  are formed by the negative electrode conductive paste layers  32   b   2  (second negative electrode  12   b ×2). The negative electrode conductive paste layers  32   b  are arranged at a predetermined pitch P along the x direction (this pitch P is the same as the pitch P illustrated in  FIG. 8 ). A second group G 2  indicating a group of the negative electrode conductive paste layers  32   b  arranged in the x direction is arranged so as to be shifted by a half of the pitch P along the x direction with respect to the adjacent second group G 2 . 
     If necessary, an insulating layer may be formed at portions of the green sheets  31   a  and  31   b  at which the conductive paste layers are not formed. 
     Subsequently, a laminate is formed by appropriately laminating the green sheet on which the conductive paste layer is not formed, the positive electrode green sheet  30   a , and the negative electrode green sheet  30   b . At this time, the green sheets  31   a  and  31   b  are laminated such that a period of the matrix pattern of the plurality of positive electrode conductive paste layers  32   a   1  and  32   a   2  and a period of the matrix pattern of the plurality of negative electrode conductive paste layers  32   b   1  and  21   b   2  are shifted by ½ of the pitch P in the x-axis direction. Specifically, the green sheets  31   a  and  31   b  are laminated such that the periods of the two positive electrode conductive paste layers  32   a   1  integrally formed and the two negative electrode conductive paste layers  32   b   1  integrally formed are shifted by a half period (½ of the pitch P) in the x-axis direction and the periods of the two positive electrode conductive paste layers  32   a   2  formed integrally and the two negative electrode conductive paste layers  32   b   2  formed integrally are shifted by a half period (½ of the pitch P) in the x-axis direction. 
     Subsequently, raw chips are prepared by dividing the laminate into a plurality of chips. Specifically, in the present embodiment, the laminate is divided into the plurality of chips along a cut line L 1  extending in the y-axis direction and a cut line L 2  extending in the x-axis direction. 
     Thereafter, the battery body  10  is obtained by firing the raw chip. 
     Subsequently, the external electrodes  14   a ,  14   b ,  15   a , and  15   b  are formed on the battery body  10 . The external electrodes  14   a ,  14   b ,  15   a , and  15   b  can be formed, for example, by curing a thermosetting resin containing a conductive resin. A plating layer may be formed on the external electrodes  14   a ,  14   b ,  15   a , and  15   b  if necessary. A protective layer may be formed on the battery body  10 . It is possible to suppress the entrance of water into the battery body  10  by forming the protective layer. 
     SUMMARY OF EMBODIMENT 
     Referring to  FIGS. 2, 3, and 6 , the first positive electrode may include a plurality of first positive electrodes drawn out to the first surface, the first negative electrode may include a plurality of first negative electrodes drawn out to the second surface, the second positive electrode may include a plurality of second positive electrodes drawn out to the second surface, the second negative electrode may include a plurality of second negative electrodes drawn out to the first surface. The battery body includes a laminated structure (laminate) in which the first positive electrode and the first negative electrode are arranged so as to be alternately laminated at an interval and the second positive electrode and the second negative electrode are arranged so as to be alternately laminated at an interval. 
     Referring to  FIGS. 2 to 5 , in the laminated structure, the first positive electrode and the second positive electrode are located on the same layer, and the first negative electrode and the second negative electrode are located on the same layer. 
     Referring to  FIGS. 2, 3, and 6 , the first surface and the second surface intersect (orthogonal) with the laminating direction of the laminated structure, and face each other in a direction intersecting (orthogonal) with a direction in which the first element and the second element are arranged. 
     Referring to  FIG. 1 , a case where the second external electrode and the third external electrode are integrally provided indicates that the battery body includes a first conductive member including a portion functioning as the second external electrode and a portion functioning as the third external electrode. In the case of  FIG. 1 , a member composed of the second external electrode  15   a  and the third external electrode  14   b  serves as the first conductive member. 
     The first conductive member is fixed to the second surface. The first conductive member has a flat plate shape. When the battery body includes the first conductive member, the first conductive member and the fourth conductive member are separated on the first surface. 
     Where the first external electrode and the fourth external electrode are integrally provided indicates that the battery body includes a second conductive member having a portion functioning as the first external electrode and a portion functioning as the fourth external electrode. 
     The second conductive member has a flat plate shape. The second conductive member is fixed to the first surface. When the battery body includes the second conductive member, the second conductive member and the third conductive member are separated on the second surface.