Analytical cell

Substrates forming an overlapping portion of an analytical cell have through holes each having a shape tapered from an outer surface of the substrate facing to outside of the overlapping portion toward an inner surface thereof facing to inside thereof. An observation window is formed between the through holes facing each other. In the overlapping portion, at least one of negative and positive electrode active materials is provided between transmission membranes of the observation window, and at least one pillar is provided between first and second positions. At the first position, edge portions of the through holes of the outer surfaces are face-to-face with each other. At the second position, edge portions of the through holes of the inner surfaces are face-to-face with each other. At least one spacer is further provided at a position shifted from the first position toward a circumferential edge of the overlapping portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-166691 filed on Aug. 26, 2015, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an analytical cell suitable for use, e.g., in an analysis of electrode reactions, etc. using an analytical instrument.

Description of the Related Art

As is well known, in an electric cell, a negative electrode active material and a positive electrode active material undergo electrode reactions, etc. in a charge-discharge process. In recent years, attempts have been made to analyze such electrode reactions during the charging/discharging process using an analytical instrument. For example, Japanese Laid-Open Patent Publication No. 2013-535795 (PCT) proposes an analytical cell which can be observed using a transmission electron microscope (TEM), and a holder for holding the analytical cell.

This analytical cell is formed by providing a negative electrode active material and a positive electrode active material (hereinafter also referred to as the electrode active material, collectively) in an overlapping portion formed by overlapping a pair of substrates. An observation window is formed at substantially the center of the overlapping portion in a direction along the surfaces of the substrates. An electron beam can be transmitted through the observation window in the overlapping direction of the overlapping portion, for allowing observation of electrode reactions, etc. in the electrode active materials. Specifically, a through hole is formed in each of the substrates. The through hole is covered with the transmission membrane from the inside of the overlapping portion. The electron beam can be transmitted through the transmission membrane. The observation window is formed between the through holes which face each other across the transmission membrane.

Further, in the analytical cell, a spacer is provided between the substrates, at an end of the overlapping portion remote from the observation window. In the structure, the substrates are spaced from each other by a predetermined distance. In the overlapping portion, at least one of the electrode active materials is provided between the transmission membranes of the observation window. Each of the electrode active materials is connected electrically to one end of the negative electrode collector or the positive electrode collector (hereinafter also referred to as the collector, collectively), in the overlapping portion. Since the other end of the collector is exposed to the outside of the overlapping portion, each of the electrode active materials is electrically connectable to the charging/discharging devices, etc. outside the overlapping portion through the collector.

That is, in the case of observing the analytical cell using a transmission electron microscope (TEM), firstly, the analytical cell is accommodated in a front end of a holder having a flow channel for allowing electrolytic solution to flow inside the overlapping portion. Thus, the electrolytic solution flows through the flow channel of the holder into the overlapping portion. The collectors are electrically connected to a charge-discharge tester or the like through the electric path of the holder. Consequently, it is possible to cause electrode reactions in the electrode active materials. At this time, an electron beam is transmitted through the observation window for carrying out the TEM observation. In this manner, it is possible to analyze the above electrode reactions.

SUMMARY OF THE INVENTION

In this regard, in the case of conducting a TEM observation of the analytical cell, when the electron beam is transmitted through the observation window, transmission of the electron beam tends to be obstructed by the electrolytic solution. Therefore, in order to obtain the observation result of the analytical cell highly accurately by improving the resolution of the image obtained as the observation result, it is required to reduce the distance by which the electron beam is transmitted through the electrolytic solution in the observation window. Stated otherwise, it is required to reduce the distance between the transmission membranes of the observation window.

On the other hand, if the distance between the transmission membranes of the observation window is excessively small, the constituent elements such as the electrode active materials are likely to be easily pressed and damaged between the transmission membranes. Consequently, the durability of the analytical cell is degraded. Therefore, for the purpose of improving the observation accuracy without degrading the durability of the analytical cell, it is desirable to adjust the distance between the transmission membranes of the observation window highly accurately in a manner that a small gap is formed between the constituent element and at least one of the transmission membranes.

However, in the above analytical cell, since only the distance between the substrates is adjusted by the thickness of the spacer provided at the end of the overlapping portion which is spaced from the observation window, it is difficult to adjust the distance between the transmission membranes of the observation window highly accurately.

Further, since the distance between the spacer and the observation window is large, for example, if an external force is applied to the analytical cell, the distance between the transmission membranes may be changed easily. That is, even if the distance between the transmission membranes of the observation window is adjusted, it is difficult to maintain the adjusted distance. Consequently, there is a concern that it is not possible to avoid the situation where the constituent elements are pressed and damaged between the transmission membranes.

A main object of the present invention is to provide an analytical cell in which it is possible to adjust the distance between transmission membranes of an observation window highly accurately, and suppress changes in the distance, whereby the observation accuracy is improved without degrading the durability.

According to an embodiment of the present invention, an analytical cell is provided. The analytical cell includes substrates overlapped with each other to form an overlapping portion. A negative electrode active material and a positive electrode active material are provided in the overlapping portion, and separately contact electrolytic solution. An observation window for transmission of an electron beam in an overlapping direction of the overlapping portion is provided in the overlapping portion. The substrates have respective through holes extending through the substrates in a thickness direction thereof. The substrates each have main surfaces on both sides thereof in the thickness direction. Each of the through holes has a shape that is tapered from an outer surface of the main surfaces that faces to the outside of the overlapping portion, toward an inner surface of the main surfaces that faces to the inside of the overlapping portion. The through holes are covered with respective transmission membranes from the inner surface side, the transmission membranes each having an electron beam permeability. The observation window is formed between the through holes facing each other across the transmission membranes. At least one of the negative electrode active material and the positive electrode active material is formed between the transmission membranes of the observation window. In the overlapping portion, at least one pillar configured to maintain the distance between the transmission membranes of the observation window is provided between a first position and a second position. The first position is a position where edge portions of the through holes of the outer surfaces of the substrates are disposed face-to-face with each other in the overlapping direction. The second position is a position where edge portions of the through holes of the inner surfaces of the substrates are disposed face-to-face with each other in the overlapping direction. At least one spacer configured to maintain the distance between the substrates is provided at a position shifted from the first position toward a circumferential edge portion of the overlapping portion. A negative electrode collector and a positive electrode collector extend from the inside of the overlapping portion and protrude outside the overlapping portion, and are electrically connected respectively to the negative electrode active material and the positive electrode active material inside the overlapping portion.

In the overlapping portion of the analytical cell of the present invention, the distance between the substrates is maintained by the spacer, and the distance between the transmission membranes of the observation window is maintained by the pillar. Since this pillar is positioned between the first position and the second position in the overlapping portion, the pillar is positioned close to the observation window. In the structure, the distance between the substrates in the overlapping portion, in particular, the distance between the transmission membranes of the observation window can be adjusted highly accurately. Further, even in the case where an external force is applied to the analytical cell, changes in the distance between the transmission membranes can be suppressed effectively.

Therefore, in this analytical cell, the distance between the transmission membranes can be adjusted to be reduced to an extent that only a slight gap is formed between the constituent elements (e.g., at least one of the negative electrode active material and the positive electrode active material) disposed between the transmission membranes of the observation window and at least one of the transmission membranes, and the distance can be maintained. That is, in order to obtain a desired resolution in the TEM observation, etc., it is possible to reduce the distance between the transmission membranes of the observation window, and prevent the constituent elements from being pressed between the transmission membranes. As a result, it becomes possible to improve the observation accuracy without degrading the durability of the analytical cell.

In the analytical cell, preferably, the pillar includes at least three pillars that are not on the same straight line. In this case, changes in the distance between the transmission membranes of the observation window can be suppressed more effectively.

In the analytical cell, preferably, the pillar includes a pair of pillars that face each other across the observation window. In this case, changes in the distance between the transmission membranes of the observation window can be suppressed more effectively.

In the analytical cell, preferably, the pillar includes one pillar provided in the vicinity of a space between the negative electrode active material and the positive electrode active material that face each other, in the overlapping portion. In this case, owing to the pillar, the distance between the transmission membranes in the vicinity of the negative electrode active material and the positive electrode active material can be maintained suitably. Thus, it is possible to effectively suppress contact of the transmission membranes with the negative electrode active material and the positive electrode active material. Further, this pillar can ensure that a sufficient space is provided between the negative electrode active material and the positive electrode active material in the overlapping portion. Thus, even in the case where an external force is applied to the analytical cell, since each of the negative electrode active material and the positive electrode active material is placed in contact with the electrolytic solution, and the electrode reactions occur suitably, it is possible to improve the observation accuracy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of an analytical cell according to the present invention will be described with reference to the accompanying drawings.

The analytical cell is suitable for use, e.g., in an analysis of electrode reactions, etc. in a negative electrode active material and a positive electrode active material based on electron beam transmission using various types of analytical instruments. For example, the analytical instrument may be a transmission electron microscope (TEM). In the case of using the TEM, the analytical cell is accommodated in a front end of a TEM holder, and an observation process is performed. Further, for example, the analytical cell may be any of a metal ion secondary cell of lithium, sodium, etc., a nickel-hydrogen cell, an alkaline-manganese cell, a metal ion air cell, a metal ion all solid cell, etc., and a fuel cell such as a solid polymer electrolyte fuel cell. Hereinafter, examples of an analytical cell made up of a lithium ion secondary cell will be described.

An analytical cell10according to an embodiment of the present invention will be described mainly with reference toFIGS. 1A to 1C, 2A and 2B. In the following description, for ease of understanding the invention, the X-axis, Y-axis, and Z-axis directions shown in the drawings are defined as the width, depth, and height (thickness) directions, respectively. In addition, in the X-axis, Y-axis, and Z-axis directions, the tip of the arrow will be referred to as one end, and the base end of the arrow will be referred to as the other end.

The analytical cell10includes a first substrate14and a second substrate16. The first substrate14and the second substrate16are overlapped with each other to form an overlapping portion12. The first substrate14may be a substrate made of silicon (Si) with a silicon nitride (Si3N4) membrane formed thereon, a substrate made of Si with an oxide covering membrane of SiO2, etc. formed thereon, or a substrate made of borosilicate glass, quartz (SiO2), or the like. Further, as shown inFIG. 1C, a through hole18is formed in the first substrate14, at a position slightly shifted from the center of the first substrate14in the depth direction toward the other end. The through hole18extends through the first substrate14in the thickness direction.

A transmission membrane20is provided on one surface of the first substrate14to cover the through hole18, and a covering membrane22is provided on the other surface of the first substrate14in a manner to expose the through hole18. The through hole18has a truncated square pyramid shape which is tapered from the other surface of the first substrate14with the covering membrane22formed thereon toward the one surface thereof with the transmission membrane20formed thereon.

That is, as shown inFIG. 2Bin an enlarged manner, in the first substrate14, an edge portion18bof the through hole18of the one surface is positioned closer to the center of the through hole18in comparison with an edge portion18aof the through hole18of the other surface.

The transmission membrane20is made of a material having an electron beam permeability (electron beam transparency) such as silicon nitride (Si3N4), silicon carbide (SiC), etc. The covering membrane22may be made of the same material as the transmission membrane20.

A negative electrode collector24, a negative electrode active material26, a positive electrode collector28, a positive electrode active material30, pillar joint portions32, and a spacer joint portion34are provided on the transmission membrane20of the first substrate14. The material suitable for the negative electrode collector24includes tungsten (W), copper (Cu), stainless steel (SUS), carbon (C), etc. Further, in the negative electrode collector24, a layered negative electrode active material26is disposed on a connector portion24apositioned right above the through hole18through the transmission membrane20in contact with the connector portion24a. The material suitable for forming the negative electrode active material26includes, for example, Li, Li alloy, Li4Ti5O12, Si, Ge, Sn, Sn alloy, Al, Al alloy, Si oxide, Sn oxide, Al oxide, carbon (C), etc.

Further, the connector portion24aand the negative electrode active material26may have a shape and a layout configuration shown inFIGS. 5D and 7D. That is, as shown inFIG. 7D, the negative electrode active material26may comprise six separate pieces including three types of quadrangular shape and one type of circular shape, and these pieces may be provided on the connector portion24a, or may extend across the connector portion24aand the transmission membrane20. In this case, it becomes easier to observe the behavior of deformation of the negative electrode active material26, etc. resulting from electrode reactions.

The material suitable for the positive electrode collector28includes gold (Au), platinum (Pt), carbon (C), aluminum (Al), etc. Further, on the transmission membrane20, the layered positive electrode active material30is disposed on a connector portion28aof the positive electrode collector28facing the connector portion24aof the negative electrode collector24in contact with the connector portion28a. The positive electrode active material30may include, for example, LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiFePO4, Li2FePO4F, LiCo1/3Ni1/3Mn1/3O2, or Li (LiaNixMnyCoz) O2, etc.

The negative electrode collector24and the positive electrode collector28including end walls thereof, but excluding the connector portions24a,28aand exposed portions24b,28b, which protrude outside the overlapping portion12as described later, are covered with electrically insulating membranes36. In this structure, in the overlapping portion12, the insulating membranes36avoid contact of the negative electrode collector24and the positive electrode collector28with electrolytic solution38contained in the overlapping portion12. Therefore, it is possible to suppress occurrence of side reactions, which are different from the electrode reactions in the negative electrode active material26and the positive electrode active material30, in the negative electrode collector24and the positive electrode collector28. Consequently, it becomes possible to analyze the electrode reactions as the analysis subjects highly accurately.

The pillar joint portion32is formed by stacking a first base portion32aon the transmission membrane20, and stacking a second base portion32bon the first base portion32a. Further, the spacer joint portion34is formed by stacking a first spacer layer34aon the transmission membrane20, and stacking a second spacer layer34bon the first spacer layer34a. End walls of the first spacer layer34aare covered with the second spacer layer34b. For example, each of the first base portion32aand the first spacer layer34amay be made of the same material as the negative electrode collector24and the positive electrode collector28. Further, each of the second base portion32band the second spacer layer34bmay be made of the same material as the above insulating membrane36. That is, as shown inFIG. 8C, the negative electrode collector24and the positive electrode collector28partially have the function as the first spacer layer34a, and the insulating membrane36partially has the function of the second spacer layer34b.

The second substrate16is made of the same material as the first substrate14. The width and the height of the second substrate16are substantially the same as the width and the height of the first substrate14, and the depth of the second substrate16is smaller than the depth of the first substrate14. A through hole40is formed in the second substrate16at a position slightly shifted from the center in the depth direction toward the other end. The through hole40extends through the second substrate16in the thickness direction. The through hole40has a truncated square pyramid shape as in the case of the through hole18of the first substrate14. That is, as shown inFIGS. 2A and 2Bin an enlarged manner, also in the second substrate16, in comparison with an edge portion40aof the through hole40of the other surface, an edge portion40bof the through hole40of one surface is positioned closer to the center of the through hole40.

Further, two injection ports42are formed in the second substrate16at positions closer to the other end in the depth direction than the through hole40. The injection ports42extend through the second substrate16in the thickness direction. A transmission membrane20is provided on one surface of the second substrate16in a manner to cover the through hole40, and expose the injection ports42. A covering membrane22is provided on the other surface of the second substrate16in a manner to expose the through hole40and the injection ports42.

As described later, the injection ports42are formed for injecting the electrolytic solution38into the overlapping portion12. After injection of the electrolytic solution38, the injection ports42are closed by seal members44of epoxy resin, etc.

The first substrate14and the second substrate16(hereinafter also referred to as the “substrate” collectively) having the above constituent elements are overlapped with each other such that the one surface of the first substrate14and the one surface of the second substrate16face each other to form the overlapping portion12. That is, among main surfaces of each of the substrates14,16on both sides in the thickness direction, the other surface where the covering membrane22is provided is an outer surface oriented to the outside of the overlapping portion12, and the one surface where the transmission membrane20is provided is an inner surface oriented to the inside of the overlapping portion12.

Pillars46and a spacer48formed as described later are interposed between the substrates14,16in the overlapping portion12. In the structure, the substrates14,16are positioned such that the through holes18,40face each other across the transmission membranes20. In the state where the distance between the substrates14,16is maintained at a predetermined distance in correspondence with the heights of the pillars46and the spacer48, etc., the substrates14,16are joined together. That is, in the overlapping portion12, an observation window50for allowing transmission of an electron beam through the transmission membranes20is formed between the through holes18,40, and a negative electrode active material26is provided between the transmission membranes20of the observation window50.

Further, as described above, since the depth of the second substrate16is small in comparison with the depth of the first substrate14, both ends of the first substrate14in the depth direction protrude out from the overlapping portion12. The portions of the negative electrode collector24and the positive electrode collector28on the first substrate14that protrude out from this overlapping portion12form exposed portions24b,28b. That is, the negative electrode collector24and the positive electrode collector28are provided on the transmission membrane20of the first substrate14such that the negative electrode collector24and the positive electrode collector28extend from the inside of the overlapping portion12and the exposed portions24b,28bare exposed from the overlapping portion12.

In this regard, as shown inFIG. 2Bin an enlarged manner, in the overlapping portion12, a position where the edge portions18a,40aof the through holes18,40of the outer surfaces of the substrates14,16are disposed face-to-face with each other in the overlapping direction (height direction) of the overlapping portion12is referred to as a first position P1. Further, in the overlapping portion12, a position where the edge portions18b,40bof the through holes18,40of the inner surfaces of the substrates14,16are disposed face-to-face with each other in the overlapping direction is referred to as a second position P2. In this case, as described above, since the through holes18,40are tapered from the outer-surface side toward the inner-surface side of the substrates14,16, the second position P2is closer to the center of the observation window50in comparison with the first position P1. In the overlapping portion12, pillars46are provided between the first position P1and the second position P2(an area shown by arrows inFIG. 2B). In the structure, owing to the pillars46, the distance between the transmission membranes20of the observation window50is maintained.

It is sufficient that at least one pillar46is provided between the first position P1and the second position P2. However, preferably, three pillars46a,46b,46care arranged as shown inFIG. 2A. These pillars46a,46b, and46ccontact the substrate16at three points which are not on the same straight line. Stated otherwise, the pillars46a,46b, and46ccontact the substrate16at three points which forms a plane. Among these pillars46a,46b, and46c, the pillars46aand46bface each other across the observation window50, and the pillar46cand the pillar46bface each other across the observation window50. Further, as shown inFIG. 1A, the pillar46cis provided adjacent to an area between the negative electrode active material26and the positive electrode active material30which face each other.

As described above, by arranging the pillars46ato46c(hereinafter also referred to as the “pillar46”, collectively), without obstructing contact of the negative electrode active material26and the positive electrode active material30with the electrolytic solution38, it is possible to suppress variation in the distance between the transmission membranes20of the observation window50. In the illustrated embodiment of the present invention, the contact surface of the pillar46which contacts the substrate16has a quadrangular shape. However, the present invention is not limited in this respect. The contact surface may have another polygonal shape, or a circular shape. Further, preferably, the maximum length of the contact surface of the pillar46is, e.g., in a range of 40 μm to 300 μm. Further, preferably, the distance between the pillar46and the second position P2is in a range of 50 μm to 500 μm.

As described later, the pillar46is formed by solid state bonding of a first pillar precursor52(seeFIGS. 10A and 10B, etc.) formed on the pillar joint portion32of the first substrate14and a second pillar precursor54(seeFIGS. 16A and 16B, etc.) formed on the transmission membrane20of the second substrate16. It should be noted that the term “solid state bonding (welding)” used in this specification means “General term for the method of welding performed at a temperature less than or equal to the melting point of base material. In the method, welding of solid state materials are performed in a pressurized state or a non-pressurized state without using brazing material.” defined in JISZ3001-2 “Welding Vocabulary Part 2: Welding Processes 4.2.7. Solid State Bonding No. 22701”.

The material suitable for the first pillar precursor52and the second pillar precursor54includes a metal such as gold (Au), copper (Cu), or aluminum (Al), or an inorganic material such as SiO2, Si. The materials of the first pillar precursor52and the second pillar precursor54may be the same, or may be different from each other. In the case where the first pillar precursor52and the second pillar precursor54are made of metal, as the solid state bonding, any of various methods, including hot pressure welding, cold pressure welding, diffusion welding, and friction pressure welding may be adopted. Further, in the case where the first pillar precursor52and the second pillar precursor54are made of inorganic material, for example, a bonding method by bringing the bonding surfaces activated by surface treatment into contact with each other may be adopted. In such a method, it is not essential to apply any load for the bonding process.

In the overlapping portion12, the spacer48is provided at a position shifted from the first position P1toward the circumferential edge portion P3(seeFIG. 1B) of the overlapping portion12, and maintains the distance between the substrates14,16. In the embodiment of the present invention, as shown inFIG. 1A, the spacer48seals sides of the overlapping portion12except a side thereof extending in the width direction at the other end in the depth direction (hereinafter referred to as the wiring line side), i.e., seals three sides of the overlapping portion12. The spacer48is formed continuously along the three sides, inward of the overlapping portion12Further, in the wiring line side, the spacer48is not formed adjacent to a transverse section extending across the wiring line side, in order for the negative electrode collector24and the positive electrode collector28to protrude from the inside to the outside of the overlapping portion12. Stated otherwise, the spacer48is formed in an area of the wiring line side other than a portion adjacent to the transverse section. That is, the spacer48is formed on the transverse section as well (seeFIG. 18AandFIG. 18B).

As described later, this spacer48is formed by solid state bonding of a first spacer precursor56(seeFIGS. 9A to 9C, etc.) formed on the spacer joint portion34of the first substrate14and a second spacer precursor58(seeFIGS. 15A to 15C, etc.) formed on the transmission membrane20of the second substrate16. The first spacer precursor56and the second spacer precursor58are made of the same material as the first pillar precursor52and the second pillar precursor54suitably. In the same manner as the pillar46, the first spacer precursor56and the second spacer precursor58are joined by solid state bonding to form the spacer48.

In the wiring line side of the overlapping portion12, for example, a seal member60of epoxy resin, etc. is provided in the area which is not sealed by the spacer48(area adjacent to the transverse section). In this structure, a liquid tight space is formed in the overlapping portion12, and filled with the electrolytic solution38. Therefore, in the analytical cell10, it is not required to generate flow of the electrolytic solution38in the overlapping portion12. Therefore, it is possible to reduce the pressure of the electrolytic solution38applied to the substrates14,16. Accordingly, it is possible to reduce the distance between the substrates14,16, and reduce the overall size of the analytical cell10.

As the electrolytic solution38, for example, it is possible to suitably use solution obtained by adding supporting electrolyte such as lithium hexafluorophosphate (LiPF6) of about 1M to propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), etc.

The analytical cell10basically has the structure as described above. In the overlapping portion12, the negative electrode active material26and the positive electrode active material30on the connector portions24a,28aof the negative electrode collector24and the positive electrode collector28, separately contact the electrolytic solution38. The negative electrode collector24and the positive electrode collector28extend from the connector portions24a,28aacross the wiring line sides, and the exposed portions24b,28bare exposed to the outside of the overlapping portion12. That is, the negative electrode active material26and the positive electrode active material30can be electrically connected to the outside of the overlapping portion12through the negative electrode collector24and the positive electrode collector28.

For example, in the TEM observation of the analytical cell10, firstly, the analytical cell10is placed on the TEM holder (not shown) in such a manner that the observation window50faces an electron beam irradiation part of the TEM. Then, the exposed portions24b,28bare electrically connected to the charge-discharge tester or the like, through an electrical path (not shown) provided in the holder to cause the electrode reactions as the observation subjects in the negative electrode active material26and the positive electrode active material30.

The analytical cell10may be produced by a known semiconductor process (see, e.g., International Publication No. WO 2008/141147). Hereinafter, a method of producing the analytical cell10according to the embodiment of the present invention will be described below with reference toFIGS. 3A to 18B. It is a matter of course that the method of producing the analytical cell10, and the order of steps or processes for production of the analytical cell10are not limited to those described in the following description. In this example, the first substrate14, the second substrate16, and the negative electrode active material26are made of silicon (Si), the positive electrode active material30is made of lithium cobaltate (LiCoO2), the transmission membrane20, the covering membrane22, and the insulating membrane36are made of silicon nitride (Si3N4), and the negative electrode collector24and the positive electrode collector28are made of tungsten (W).

The analytical cell10can be obtained by forming the above constituent elements on the first substrate14and the second substrate16separately, and then bonding the first pillar precursor52and the second pillar precursor54together, and the first spacer precursor56and the second spacer precursor58together by solid state bonding. Then, at the outset, steps of providing the constituent elements including the first pillar precursor52and the first spacer precursor56on the first substrate14will be described.

Firstly, as shown inFIGS. 3A to 3C, both surfaces of the first substrate14are polished, and each of the surfaces of the first substrate14is covered with a silicon nitride membrane by chemical vapor deposition (CVD). The silicon nitride membrane formed on the one surface of the first substrate14is used as the transmission membrane20, and the silicon nitride membrane formed on the other surface of the first substrate14is used as the covering membrane22.

Next, the transmission membrane20of the first substrate14is covered with a photoresist (not shown), and a photolithography process is performed. In the photolithography process, the photoresist is removed only on portions of the transmission membrane20where the negative electrode collector24, the positive electrode collector28, the pillar joint portion32, and the spacer joint portion34should be formed, whereby only the portions of the transmission membrane20are exposed to outside.

Next, using the physical vapor deposition (PVD) method, one surface of the first substrate14is covered with a tungsten membrane, and thereafter, the entire photoresist is removed (by lift-off processing). As a result, as shown inFIGS. 4A to 4C, the negative electrode collector24, the positive electrode collector28, the first base portions32aof the pillar joint portions32, and the first spacer layer34aof the spacer joint portion34, which are made up of the tungsten membranes, are formed on the transmission membrane20of the first substrate14. In this case, the number and layout of the first base portions32a, and the shape of the connector portion24aof the negative electrode collector24are set as shown inFIG. 4D.

Next, the one surface of the first substrate14is covered with a silicon nitride membrane by chemical vapor deposition (CVD). Then, this silicon nitride membrane is covered with a photoresist, and a photolithography process is performed. As a result of this process, the photoresist is left only on portions of the silicon nitride membrane that cover a portion of the negative electrode collector24excluding the connector portion24aand the exposed portion24b, and a portion of the positive electrode collector28excluding the connector portion28aand the exposed portion28b, and also cover the first base portions32aand the first spacer layer34a. It should be noted that the photoresist is also left on portions of the silicon nitride membrane that cover the end walls of the above portions of the negative electrode collector24and the positive electrode collector28, and the end walls of the first spacer layer34a.

Next, for example, a dry etching process such as a reactive ion etching process is carried out using the photoresist as a mask. In this process, the silicon nitride membrane covered with the residual photoresist as described above are protected. Thereafter, the entire photoresist is removed. Consequently, as shown inFIGS. 5A to 5D, the silicon nitride membrane is formed so as to cover the portion of the negative electrode collector24excluding the connector portion24aand the exposed portion24b, the portion of the positive electrode collector28excluding the connector portion28aand the exposed portion28b, the first base portion32a, and the first spacer layer34a. It is a matter of course that the end walls of the above portions of the negative electrode collector24and the positive electrode collector28, and the end walls of the first spacer layer34aare also covered with the silicon nitride membrane.

The part of the silicon nitride membrane covering the negative electrode collector24and the positive electrode collector28form the insulating membrane36, and the part of the silicon nitride membrane covering the first base portions32aforms second base portions32b, and the silicon nitride membrane covering the first spacer layer34aforms the second spacer layer34b. That is, the first base portions32aand the second base portions32bform the pillar joint portions32, and the first spacer layer34aand the second spacer layer34bform the spacer joint portion34.

Next, the one surface of the first substrate14is covered with a photoresist, and a photolithography process is performed. In the photolithography process, the photoresist on a portion of the one surface where the positive electrode active material30should be formed is removed. As a result, only the portion of the connector portion28aof the positive electrode collector28where the positive electrode active material30should be formed is exposed.

Next, one surface of the first substrate14is covered with a lithium cobaltate membrane by radio frequency spattering (RF spattering), and thereafter, the entire photoresist is removed. As a result, as shown inFIGS. 6A to 6C, the positive electrode active material30made up of the lithium cobaltate membrane is formed on the connector portion28aof the positive electrode collector28. For the purpose of improving the activity of the positive electrode active material30, annealing treatment for enhancing the crystallinity of the positive electrode active material30may be applied, or the membrane thickness or the shape pattern of the positive electrode active material30may be changed.

Next the one surface of the first substrate14is covered with a photoresist, and a photolithography process is performed. In the photolithography process, the photoresist on a portion where the negative electrode active material26should be formed is removed. As a result, only the portion of the connector portion24aof the negative electrode collector24where the negative electrode active material26should be formed is exposed.

Next, the one surface of the first substrate14is covered with a silicon membrane by RF spattering, and thereafter, the entire photoresist is removed. As a result, as shown inFIGS. 7A to 7D, the negative electrode active material26made up of a silicon membrane is formed on the connector portion24aof the negative electrode collector24.

Next the one surface of the first substrate14is covered with a photoresist, and a photolithography process is performed. In the photolithography process, the photoresist on portions where the first pillar precursor52and the first spacer precursor56should be formed is removed. As a result, the second base portions32band the second spacer layer34b, and only the transverse sections of the negative electrode collector24and the positive electrode collector28are exposed. In this regard, the thickness of photoresist should be determined to have a value which is about twice to 10 times as large as desired heights of the first pillar precursor52and the first spacer precursor56.

Next, using the PVD method, the one surface of the first substrate14is covered with a chromium membrane, and then, covered with a gold membrane. At the time of forming the membranes, using a membrane quantity measuring instrument as an accessory device of the PVD apparatus, in-situ monitoring of the membrane quantity (thickness) is conducted, and the deposited membrane thickness is controlled. In this manner, the membrane thickness control in the order of several nanometers can be performed. Thereafter, the entire photoresist is removed. Consequently, as shown inFIGS. 8A to 8D, the first pillar precursors52and the first spacer precursor56each comprising a stack body of the chromium membrane and the gold membrane are formed on the transmission membrane20of the first substrate14. As shown inFIG. 10Ain an enlarged manner, the area of the surface at one end side in the height direction of the first pillar precursor52may be slightly smaller than the area of the pillar joint portion32. In this case, it becomes possible to form the first pillar precursor52on the pillar joint portion32further reliably.

Next, on the other surface of the first substrate14, the covering membrane22is covered with a photoresist, and a photolithography process is performed. As a result, the photoresist is removed to expose part of the covering membrane22provided on a portion where the through hole18should be formed in the first substrate14.

Next, a dry etching process is carried out using the photoresist as a mask. As a result, only the part of the covering membrane22exposed from the photoresist is removed from the first substrate14. In this manner, after removing the part of the covering membrane22provided on the portion of the first substrate14where the through hole18should be formed in the first substrate14, the entire photoresist is removed.

Next, as shown inFIGS. 9A to 9C, andFIGS. 10A and 10B, a wet etching process (through hole etching) is applied to the other surface of the first substrate14to thereby form the through hole18. In this manner, the through hole18is formed in the first substrate14. The through hole18is covered with the transmission membrane20, from the one surface side of the first substrate14. The one surface of the first substrate14may be covered with an alkali-resistant surface protection layer (not shown) before performing the wet etching process. In this case, the one surface of the first substrate14can be protected by the alkali-resistant surface protection layer. Further, the alkali-resistant surface protection layer should be removed by dry etching or removing liquid after forming the through hole18as described above.

As shown inFIGS. 10A and 10Bin an enlarged manner, the first pillar precursors52are provided between the edge portion18aof the through hole18of the other surface of the first substrate14and the edge portion18bof the through hole18of the one surface of the first substrate14. Further, in the surface of the first substrate14, the first spacer precursor56is provided outside the edge portion18aof the through hole18.

Also on the second substrate16, as shown inFIGS. 11A to 11C, in the same manner as in the case of the first substrate14, the transmission membrane20and the covering membrane22are provided. Next, the one surface of the second substrate16is covered with a photoresist, and a photolithography process is performed. As a result, the photoresist of portions where the second pillar precursors54and the second spacer precursor58should be formed is removed, and the transmission membrane20is exposed from the portions. In this regard, the thickness of the photoresist should be determined to have a value which is about twice to 10 times as large as desired heights of the second pillar precursor54and the second spacer precursor58.

Next, using the PVD method, the one surface of the second substrate16is covered with a chromium membrane, and then, covered with a gold membrane. At the time of forming the membranes, using a membrane quantity measuring instrument as an accessory device of the PVD apparatus, in-situ monitoring of the membrane quantity (thickness) is conducted, and the deposited membrane thickness is controlled. In this manner, the membrane thickness control in the order of several nanometers can be performed. Thereafter, the entire photoresist is removed. Consequently, as shown inFIGS. 12A to 12C, the second pillar precursors54and the second spacer precursor58each comprising a stack body of the chromium membrane and the gold membrane are formed on the transmission membrane20of the second substrate16.

Next, the one surface of the second substrate16is covered with a photoresist, and a photolithography process is performed. As a result, the photoresist is partly removed so as to expose part of the transmission membrane20provided on portions where the injection ports42should be formed in the second substrate16.

Next, a dry etching process is carried out using the photoresist as a mask. As a result, only the part of the transmission membrane20provided on the portions where the injection ports42should be formed is removed. Thereafter, the entire photoresist is removed. In this manner, as shown inFIGS. 13A to 13C, only the part of the transmission membrane20provided on the portions of the second substrate16where the injection ports42should be formed is removed, and the portions of the second substrate16are exposed.

Next, the covering membrane22on the other surface of the second substrate16is covered with a photoresist, and a photolithography process is performed. As a result, the photoresist is partly removed to expose part of the covering membrane22provided on portions where the through hole40and the injection ports42of the second substrate16should be formed.

Next, a dry etching process is carried out using the photoresist as a mask. As a result, only the part of the covering membrane22provided on the portions where through hole40and the injection ports42should be formed is removed. Thereafter, the entire photoresist is removed. In this manner, as shown inFIGS. 14A to 14C, only the part of the covering membrane22provided on the portions of the second substrate16where the through hole40and the injection ports42should be formed are removed, and the portions of the second substrate16are exposed.

Next, as shown inFIGS. 15A to 15C, 16A, 16B, a wet etching process (through hole etching) is applied to the second substrate16to thereby form the through hole40and the injection ports42. As a result, the through hole40covered with the transmission membrane20, from the one surface side of the second substrate16is formed in the second substrate16. Further, the injection ports42exposed from the transmission membrane20and the covering membrane22are formed in the second substrate16.

As shown inFIGS. 16A and 16Bin an enlarged manner, the second pillar precursors54are arranged between the edge portion40aof the through hole40of the other surface of the second substrate16and the edge portion40bof the through hole40of the one surface of the second substrate16. Further, in the surface of the second substrate16, the second spacer precursor58is arranged outside the edge portion40aof the through hole40.

A pair of the first pillar precursor52and the second pillar precursor54which correspond to each other should be provided at respective positions of the first substrate14and the second substrate16where the pillar46should be formed. That is, in the embodiment of the present invention, as shown inFIGS. 10A and 16A, though three pairs of the first pillar precursors52and the second pillar precursors54are provided, the present invention is not limited in this respect as long as at least one pair of the first pillar precursor52and the second pillar precursor54are provided.

After the above series of processes, the first substrate14and the second substrate16having the various constituent elements are overlapped with each other, and the first pillar precursor52and the second pillar precursor54which correspond to each other are brought into contact with each other, and the first spacer precursor56and the second spacer precursor58which correspond to each other are brought into contact with each other. At this time, for example, an adjustment is made in a manner that the edge portions18b,40bof the through holes18,40provided on the one surface side of the first substrate14and the second substrate16are overlapped and in alignment with each other in a plan view. Thus, the first substrate14and the second substrate16can be positioned easily and highly accurately in a manner that the through holes18,40are arranged face-to-face with each other across the transmission membranes20to thereby form the observation window50.

In order to suppress variation in the contact area between the first spacer precursor56and the second spacer precursor58that are placed into contact with each other as described above, preferably, the protruding end surfaces (bonding surfaces) of the first spacer precursor56and the second spacer precursor58have different lengths in the lateral direction. In the structure, when a load is applied to the first spacer precursor56and the second spacer precursor58so as to be placed in contact, as described later, it is possible to suppress the occurrence of pressure variation, and improve the bonding uniformity by the spacer48.

In the embodiment where the contact surfaces (bonding surfaces) of the first pillar precursor52and the second pillar precursor54are made of gold, and the contact surfaces (bonding surfaces) of the first spacer precursor56and the second spacer precursor58are made of gold, solid state bonding should be performed as follows: Specifically, the bonding surfaces of the first pillar precursor52and the second pillar precursor54are brought into contact with (abutment against) each other, and the bonding surfaces of the first spacer precursor56and the second spacer precursor58are brought into contact with (abutment against) each other. In this state, a pressure load in a range of 0.2 to 2.0 kgf, preferably 1.0 kgf, per the unit bonding area of 1 mm2should be applied to the first pillar precursor52and the second pillar precursor54, and the first spacer precursor56and the second spacer precursor58, e.g., at temperature in a range of 300 to 400 C.°, preferably at temperature of 300 C.° for 15 to 60 minutes. In this manner, as shown inFIGS. 17A to 17C, the first pillar precursor52and the second pillar precursor54are bonded together firmly to obtain the pillar46, and the first spacer precursor56and the second spacer precursor58are bonded together firmly to form the spacer48.

In the case where each of the above bonding surfaces is made of aluminum, the same load as described above should be applied at temperature in a range of 400 to 450° C., preferably at temperature of 400° C., for the same time period as described above. Alternatively, in the case where each of the bonding surfaces are made of copper, the same load as described above should be applied at temperature in a range of 350 to 450° C., preferably at temperature of 350° C., for the same time period as described above.

Further, in the case where each of the bonding surfaces is made of the above-described inorganic material, the bonding surfaces should be activated before formation of the overlapping portion12. Activation of such boding surfaces can be performed using existing devices such as a room-temperature wafer bonder “BOND MEISTER” (product name) of Mitsubishi Heavy Industries, Ltd., a surface activation wafer bonding kit (Model type: WP-100) of PMT Corporation, or the like.

More specifically, sputter etching using ion beams, plasma, etc. may be applied to each of the bonding surfaces in a vacuum chamber at room temperature under high vacuum. In this manner, it is possible to remove an oxide film and absorption films comprising water, organic material, etc., formed on the bonding surfaces to thereby expose atoms having bonds, i.e., activate the bonding surfaces. If the bonding surfaces activated in this manner are brought into contact with each other, a bonding force is generated between the bonding surfaces. As a result, it is possible to obtain the pillar46by firmly bonding the first pillar precursor52and the second pillar precursor54, and obtain the spacer48by firmly bonding the first spacer precursor56and the second spacer precursor58. The bonding conditions in this process should be determined appropriately based on the material, shape, or the like of the first pillar precursor52and the second pillar precursor54, and the first spacer precursor56and the second spacer precursor58.

By forming the pillar46and the spacer48as described above, in the state where the substrates14,16jointly form the overlapping portion12, the substrates14,16are joined together. Further, the transmission membranes20of the observation window50are kept spaced from each other by a predetermined distance in correspondence with the heights of the pillar46and the pillar joint portion32. Further, the transmission membranes20of the substrates14,16are kept spaced from each other by a predetermined distance in correspondence with the heights of the spacer48and the spacer joint portion34.

This pillar46is formed without melting the first pillar precursor52and the second pillar precursor54. Therefore, the height of the pillar46becomes substantially equal to the sum of the heights of the first pillar precursor52and the second pillar precursor54. Likewise, the height of the spacer48becomes substantially equal to the sum of the heights of the first spacer precursor56and the second spacer precursor58. That is, by adjusting the heights of the first pillar precursor52, the second pillar precursor54, the first spacer precursor56, and the second spacer precursor58, it is possible to make settings of the distance between the transmission membranes20of the substrates14,16easily.

Then, the electrolytic solution38(seeFIGS. 1A to 1C) is injected from the injection ports42shown inFIGS. 18A and 18B, and a space between the first substrate14and the second substrate16is filled with the electrolytic solution38. Thereafter, the seal member60is provided adjacent to the transverse section on the first substrate14. That is, the spacer48is not formed in a portion where the first spacer precursor56is not formed, and a space is formed between the second spacer precursor58and the transmission membrane20of the first substrate14. By providing the seal member60in this space, it is possible to seal the outer circumference of the overlapping portion12.

Stated otherwise, by providing the spacer48to have the above shape and layout configuration, it is possible to seal the major part of the outer circumference of the overlapping portion12by the spacer48. Therefore, the seal member60is provided only in the remaining portion which is not sealed by the spacer48. Further, by closing the injection ports42by the seal member44, it is possible to easily form a liquid tight space in the overlapping portion12. As a result, the negative electrode active material26provided between the transmission membranes20of the observation window50and the positive electrode active material30provided in the overlapping portion12separately contact the electrolytic solution38, to form a lithium ion cell. That is, with the simple processes, the analytical cell10can be obtained at low cost.

In the above structure, in the overlapping portion12of the analytical cell10, the distance between the substrates14,16is maintained by the spacer48, and the distance between the transmission membranes20of the observation window50is maintained by the pillar46. Since the pillar46is positioned between the first position P1and the second position P2in the overlapping portion12, the pillar46is provided close to the observation window50. Therefore, the distance between the substrates14,16of the overlapping portion12, in particular, the distance between the transmission membranes20of the observation window50can be adjusted highly accurately. Further, even in the case where an external force is applied to the analytical cell10, it is possible to suppress occurrence of changes in the distance between the transmission membranes20effectively.

Therefore, in this analytical cell10wherein constituent elements such as the negative electrode active material26is provided between the transmission membranes20of the observation window50, the distance between the transmission membranes20can be adjusted to be reduced to an extent that only a slight gap is formed between the constituent elements and the transmission membrane20of the second substrate16, and the distance can be maintained. That is, in order to obtain a desired resolution in the TEM observation, etc., it is possible to reduce the distance between the transmission membranes20of the observation window50, and prevent the negative electrode active material26, etc. from being pressed between the transmission membranes20. As a result, it becomes possible to improve the observation accuracy without degrading the durability of the analytical cell10.

Further, in this analytical cell10, the pillar46cis provided in the vicinity of the space between the negative electrode active material26and the positive electrode active material30which face each other, in the overlapping portion12. In the structure, the distance between the transmission membranes20in the vicinity of the negative electrode active material26and the positive electrode active material30can be maintained suitably. Thus, it is possible to suppress contact of the transmission membranes20with the negative electrode active material26and the positive electrode active material30effectively. Further, even in the case where an external force is applied to the analytical cell10, since it is possible to secure contact between the electrolytic solution38and each of the negative electrode active material26and the positive electrode active material30, the electrode reactions occur suitably, and improvement in the observation accuracy is achieved.

Further, in the presence of the pillars46and the spacer48each obtained by solid state bonding, it is possible to firmly join the substrates14,16together. Accordingly, even in the case where the analytical cell10is attached to the holder, and observation is performed using an electron microscope in a high vacuum atmosphere, it is possible to effectively suppress positional displacement between the substrates14,16and occurrence of changes in the distance between the transmission membranes20of the observation window50.

The present invention is not limited to the embodiments described above, and various modifications can be made without deviating from the scope of the present invention.

For example, in the analytical cell10according to the above embodiment of the present invention, the solid state joint of the first pillar precursor52and the second pillar precursor54form the pillar46to firmly join the transmission membranes20of the observation window50together. However, the present invention is not limited in this respect. For example, the pillar46may comprise a stack body formed only by bringing the first pillar precursor52and the second pillar precursor54in contact with each other, whereby the analytical cell10may be obtained easily and efficiently.

Further, in the analytical cell10according to the above embodiment, the pillar46and the spacer48are formed respectively on the pillar joint portion32and the spacer joint portion34formed on the transmission membrane20of the first substrate14. However, the present invention is not limited in this respect. The pillar joint portion32may be provided on both of the transmission membranes20of the first substrate14and the second substrate16. Alternatively, the pillar joint portion32may be provided on the transmission membrane20of the second substrate16, instead of the first substrate14. Further, the pillar46may be formed in the overlapping portion12without providing the pillar joint portion32. The same applies to the spacer joint portion34.

Further, in the analytical cell10according to the above embodiment, among the negative electrode active material26and the positive electrode active material30, only the negative electrode active material26is provided between the transmission membranes20of the observation window50. However, the present invention is not limited in this respect. Both of the negative electrode active material26and the positive electrode active material30or only the positive electrode active material30may be provided between the transmission membranes20of the observation window50. Also in this case, the same working effects and advantages as in the case of the analytical cell10according to the above embodiment are obtained.

Furthermore, in the case where the analytical cell10or the like of the above embodiment is not the lithium-ion secondary cell but the nickel-hydrogen cell, for example, a positive electrode of nickel hydroxide, a negative electrode of any of various hydrogen storing alloys, and an electrolytic solution of an aqueous potassium hydroxide solution KOH(aq) may be used. Alternatively, in the case where the analytical cell10is the alkaline-manganese cell, for example, a positive electrode of manganese dioxide/graphite, a negative electrode of zinc, and an electrolytic solution of KOH(aq) may be used.

Further, the analytical cell10can be used in an analysis not only in the TEM but also in any general analytical instrument using an electron beam.

Embodiment Example

Using the above steps, a test specimen of the analytical cell10according to the embodiment example was produced. Specifically, as the first substrate14, a silicon substrate having the width of 4.0 mm, the depth of 4.0 mm, and the thickness of 200 μm was adopted. A through hole18having the width of 60 μm and the depth of 60 μm was formed in the silicon substrate. Further, as the transmission membrane20, a silicon nitride membrane having the thickness of 80 nm was adopted. As the negative electrode collector24and the positive electrode collector28, tungsten membranes having the thickness of 120 nm were adopted.

The connector portion24aof the negative electrode collector24had a shape shown inFIG. 5D. As the negative electrode active material26, silicon having a shape shown inFIG. 7Dwas adopted. As the insulating membrane36, a silicon nitride membrane having the thickness of 160 nm was adopted. The layout configuration, the number, and the shape of the first pillar precursors52were set as shown inFIG. 10A.

The pillar joint portion32was formed by covering a first base portion32a(thickness of 120 nm) with a second base portion32b(thickness of 160 nm). The first base portion32acomprises a tungsten membrane formed in the same manner as the negative electrode collector24and the positive electrode collector28. The second base portion32bcomprises a silicon nitride membrane formed in the same manner as the insulating membrane36. That is, the thickness of the pillar joint portion32was 280 nm. Further, the surface of the pillar joint portion32at one end in the height direction was formed into a square shape with the side length of 80 μm.

The first pillar precursor52was a stack body including a chromium membrane formed on the pillar joint portion32and a gold membrane formed on the chromium membrane. The thickness of this chromium membrane was 50 nm, and the thickness of the gold membrane was 200 nm. Therefore, the height of the first pillar precursor52was 250 nm. Further, the surface of the first pillar precursor52at one end in the height direction was formed into a square shape with the side length of 60 μm.

The spacer joint portion34was formed in the same manner as the pillar joint portion32. The first spacer precursor56is formed on the spacer joint portion34in the same manner as the first pillar precursor52. Further, each of the sides of the first spacer precursor56in the depth direction and in the width direction had the length of 3.75 mm. The surface (bonding surface) of the first spacer precursor56at one end in the height direction had the lateral length of 0.1 mm. That is, the surface area of the bonding surface of the first spacer precursor56was 1.25 mm2.

Further, as the second substrate16, a silicon substrate having the width of 4.0 mm, the depth of 4.0 mm, and the thickness of 200 μm was adopted. A through hole40having the same shape as the through hole18of the first substrate14, and injection ports42each having the width of 500 μm and the depth of 500 μm were formed in the silicon substrate. The layout configuration, the number, and the shape of the second pillar precursors54were set as shown inFIG. 16A.

The second pillar precursor54was a stack body including a chromium membrane formed on the transmission membrane20and a gold membrane formed on the chromium membrane. The thickness of this chromium membrane was 50 nm, and the thickness of the gold membrane was 400 nm. Therefore, the height of the second pillar precursor54was 450 nm. Further, the surface (bonding surface) of the first pillar precursor52at one end in the height direction was formed into a square shape with the side length of 60 μm.

The second spacer precursor58was formed in the same manner as the second pillar precursor54. Further, each of the sides of the second spacer precursor58in the depth direction and in the width direction had the length of 3.8 mm. The surface (bonding surface) of the second spacer precursor58at the other end in the height direction had the lateral length of 0.15 mm. That is, the surface area of the bonding surface of the second spacer precursor58was 2.19 mm2.

Therefore, the bonding area for bonding the first pillar precursor52and the second pillar precursor54by solid state bonding is 0.0108 mm2(60 μm×60 μm×3=0.0108 mm2). Further, since the total value of the heights of the first pillar precursor52and the second pillar precursor54is 700 nm, the preset value of the height of the pillar46is 700 nm.

The bonding area for bonding the first spacer precursor56and the second spacer precursor58by solid state bonding was 1.25 mm2. Further, since the total value of the lengths of the first spacer precursor56and the second spacer precursor58was 700 nm, the preset value of the height of the spacer48was 700 nm.

That is, in the analytical cell10according to the embodiment example, 980 nm, which was the total value of the heights of the pillar46(spacer48) and the pillar joint portion32(spacer joint portion34), was used as a target setting value of the distance between the transmission membranes20of the substrates14,16.

Then, the first substrate14and the second substrate16were overlapped with each other, and positioned as described above, so that the bonding surfaces of the first pillar precursor52and the second pillar precursor54were brought into contact with each other, and the bonding surfaces of the first spacer precursor56and the second spacer precursor58were also brought into contact with each other. Then, solid state bonding was performed by applying a load of 1000 g at 350° C. for 30 minutes to thereby join the substrates14,16together, whereby the overlapping portion12was formed.

In this overlapping portion12, it was confirmed that the distance between the transmission membranes20of the substrates14,16was substantially 1000 nm. That is, as a result of obtaining the overlapping portion12as described above, the distance between the transmission membranes20of the substrates14,16, in particular, the distance between the transmission membranes20of the observation window50was able to be set at substantially the target setting value.

Next, the electrolytic solution38was prepared by dissolving LiPF6, at the concentration of 1M, in a solution obtained by mixing EC and EMC at the ratios of 3:7. The resulting electrolytic solution38was injected into the overlapping portion12through the injection ports42. Thereafter, a seal member60made of an epoxy resin was provided to seal the area around the transverse section of the overlapping portion12. Further, the injection ports42were closed by the seal members44of epoxy resin. In this manner, in the overlapping portion12, the negative electrode active material26and the positive electrode active material30separately contact the electrolytic solution38, and a test specimen of the analytical cell10, which forms a lithium ion cell, according to the embodiment example was obtained.

In the test specimen of this analytical cell10, it was confirmed that the distance between the transmission membranes20of the observation window50was about 1000 nm, and no damage was caused in any of the transmission membranes20and the negative electrode active material26.

Comparative Example

A test specimen of an analytical cell according to a comparative example was prepared by the same steps as those for the test specimen of the analytical cell10according to the embodiment of the present invention, except that no pillar46was formed in the comparative example. In the test specimen of the analytical cell according to the comparative example, it was confirmed that, when substrates14,16were stacked together, and a load was applied for solid state bonding of the first spacer precursor56and the second spacer precursor58, damage was caused in the transmission membranes20of the observation window50. Therefore, solid state bonding was cancelled, and the overlapped first and second substrates14,16were separated away from each other. One surface of each of the first substrate14and the second substrate16was observed using an optical microscope. As a result, part of the transmission membrane20peeled off from the second substrate16was adhered to the negative electrode collector24of the first substrate14, and part of the transmission membrane20covering the through hole40of the second substrate16was lost.

As described above, since the analytical cell10according to the embodiment of the present invention has the pillars46and the spacer48, it is possible to highly accurately adjust and maintain the distance between the transmission membranes20of the observation window50. Further, it is possible to avoid damage to the constituent elements caused by being pressed between the transmission membranes20. Therefore, it is possible to reduce the distance between the transmission membranes20of the observation window50, and improve the observation accuracy without degrading the durability of the analytical cell10.