JP2015216042A - Method for observing lithium ion battery, test lithium ion battery, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for observing a lithium ion battery, by which a correct microscope observation can be performed even if a section for observation is formed by a mechanical cutting process.SOLUTION: A method for observing a lithium ion battery comprises the steps of: preparing an observation cell having a cell main body (30) housing a holding tool (42) for holding a test lithium ion battery, which has a positive electrode plate, a negative electrode plate and a separator, and a flange (31) engaged with the cell main body in a hermetic manner, in which an observation window including a transparent plate (36) is formed; subsequently, cutting a test lithium ion battery along a reference plane provided on the holding tool, thereby forming an observing section (42a) orthogonal to the positive and negative electrode plates; further, removing an active material put out of a network of the battery owing to the cutting process; filling a deformable transparent filler in between the transparent plate and the observing section; and casting an illumination light on the observing section of the lithium ion battery structure through the transparent plate and the transparent filler to take an image of the observing section of the lithium ion battery structure in observation.

Description

  The present invention relates to a method for observing a lithium ion battery for microscopic observation of a test lithium ion battery used in a performance test, a test lithium ion battery, and a method for manufacturing the same.

  Lithium ion secondary batteries are used as power supply devices for electric vehicles and portable terminals, and research and development of lithium ion secondary batteries are progressing. In the research and development of lithium ion batteries, it is possible to collect important data by observing the phenomenon that occurs inside the battery during charging and discharging from the outside of the battery. As a method for observing changes in the state of the positive electrode and the negative electrode active material during charge / discharge from the outside, a method of observing an observation cross section of a test lithium ion battery with a confocal microscope is known (for example, see Patent Document 1). According to this observation method, it is clearly observed that the color of graphite as the negative electrode active material changes from gray to blue to red to gold according to the state of charge, and information useful for selecting a material for the lithium ion battery is obtained. It became possible. In particular, the state of charge, which is the amount of Li ions intercalated in the active material, can be grasped from the change in color of the active material during charging, and information useful for research and development can be obtained.

As a method for observing a test lithium ion battery used in a performance test, a battery structure including a positive electrode plate, a negative electrode plate and a separator and an insulating film constituting an insulating case are fixed with a fixing jig, and a reference for the fixing jig A method of cutting a battery structure along a surface to form an observation cross section is known (for example, see Patent Document 2). In this known observation method, after forming the observation cross section, the transparent plate is fixed to the reference surface of the fixing jig, the electrolytic solution is sealed in the insulating case, and then the observation cross section is observed through the transparent plate. .

An observation method using a pot-type observation cell is also known as another observation method for a lithium ion battery for testing (see, for example, Patent Document 3). In this known method for observing a lithium ion battery for testing, a positive electrode plate, a negative electrode plate and a separator are held by a holding tool to produce a lithium ion battery structure. Subsequently, the battery structure is cut along the reference surface of the holding tool to form an observation cross section. After the observation cross section is formed, the holding tool is accommodated in the cell main body, the flange on which the observation window is formed is hermetically coupled to the cell main body, and the observation cross section is microscopically observed through the observation window of the flange.
Japanese Patent No. 5388078 JP 2013-239263 A JP 2014-32745 A

  In the lithium ion battery observation method described above, the observation cross section of the battery structure is accurately positioned with respect to the transparent plate constituting the observation window. It is possible to observe, and it is possible to externally observe the state change of the active material during charge and discharge. However, since the observation cross section is formed by mechanically cutting the positive electrode plate, the separator, and the negative electrode plate, the observation cross section is electrically connected to the adjacent active material due to the stress generated during the cutting. A disconnected active material is generated, and it has been found that such an active material acts as a shield against illumination light and is a factor that hinders internal observation. That is, the active material of the positive electrode and the negative electrode is electrically connected to the adjacent active material through the binder and the conductive auxiliary agent, and a conduction path (network) is formed between the negative electrode current collector and the positive electrode current collector. Form. Then, electrons flow between the negative electrode current collector and the positive electrode current collector through a conduction path formed by the active material, and Li ions flow through a gap between the active materials. On the other hand, when the observation cross section is formed by mechanically cutting the battery structure in which the positive electrode plate, the separator, and the negative electrode plate are overlapped, a cutting stress acts on the active material existing on the cut surface, As a result, an active material that is disconnected from the electrical connection is formed. Since such an active material is not connected to the conduction path between the current collectors, it does not contribute to charging / discharging. Therefore, when such an active material exists, it becomes a shielding object with respect to the illumination light radiate | emitted from the microscope, and will obstruct microscope observation.

An object of the present invention is to provide a method for observing a lithium ion battery that enables accurate microscopic observation even when the observation cross section is formed by a mechanical cutting process.
Furthermore, an object of the present invention is to provide a test lithium ion battery and a test lithium ion battery capable of accurately observing a change in the state of the active material during charge and discharge even when the observation cross section is formed by mechanically cutting the lithium ion battery structure. It is to realize a manufacturing method.

An observation method of a lithium ion battery according to the present invention is an observation method of a lithium ion battery in which an observation cross section orthogonal to a positive electrode plate and a negative electrode plate of a lithium ion structure having a positive electrode plate, a negative electrode plate, and a separator is observed with a microscope,
Preparing a cell for observation having a cell main body for storing a holding tool for holding a lithium ion battery structure, an observation window including a transparent plate, and a flange for sealingly engaging with the cell main body;
An observation cross section forming step of cutting the lithium ion battery structure along a reference plane provided on a holding tool to form an observation cross section orthogonal to the positive electrode plate and the negative electrode plate;
Removing the active material removed from the battery network by the cutting process;
Storing the test lithium ion battery in the cell body such that the observation cross section faces the transparent plate;
Filling the observation cross section with an optically transparent and deformable filler;
Projecting illumination light through the transparent plate and the filler constituting the observation window toward the observation cross section of the lithium ion battery structure, and capturing an image of the observation cross section of the lithium ion battery structure. It is characterized by.

  When this inventor cut | disconnected a lithium ion battery structure, an observation cross section was formed, and when it observed from the outside, it turned out that the active material which does not contribute to charging / discharging exists in an observation cross section. That is, the individual active materials of the negative electrode and the positive electrode are combined with the adjacent active material through the binder and the conductive auxiliary agent to form a conduction path (network). And an electron distribute | circulates through the network formed with an active material, and Li ion distribute | circulates through the clearance gap between active materials. On the other hand, when an observation cross section is formed by a mechanical cutting process, the bond with the binder is broken by the cutting process, and an active material that is disconnected from the adjacent active material is generated. Since such an active material does not perform charging / discharging, the malfunction which observes the active material which does not perform charging / discharging operation | movement will generate | occur | produce, and will obstruct microscope observation. In order to solve this problem, in the present invention, after the cutting process is performed, the step of removing the active material that is disconnected from the network due to the bond between the adjacent active material and the binder is removed. By removing the active material from the cut surface, the active material connected to the network (so-called “living active material”) mainly exists on the surface of the observation cross section, so focus on the surface of the observation cross section. By observing under a microscope, it is possible to observe a change in state of the active material that is actually charged and discharged. At this time, since the active material that has lost the bond with the binder does not have a binding force between the adjacent active materials, the binder is simply pressed against the cut surface with a relatively weak adhesive sheet member. It is possible to remove the active material that has deviated from the bonding force of. When this inventor actually performed the active material removal process and observed with the microscope, it was confirmed that the color change of the active material during charging / discharging can be clearly observed over almost the entire observation cross section.

  However, when the active material is removed in the observation cross section, a minute concave space is formed between the separator and the current collector foil. When the electrolyte is sealed in this state, the concave space, that is, the observation cross section is formed. An electrolytic solution reservoir is formed between the surface of the substrate and the transparent plate constituting the observation window. On the other hand, during charging, Li ions are supplied from the positive electrode to the negative electrode through the separator, so that excess Li ions are accumulated in the electrolyte reservoir and charging / discharging of the active material in which there are excessive Li ions in the surroundings. You will observe the state change inside. In this case, the state change of the active material under an abnormal environment in which Li ions are excessively observed is observed, and a situation in which analysis data accurately matching with actual battery operation cannot be obtained.

  In order to solve the above-described problems, in the present invention, an optically transparent deformable filler is filled between the transparent plate constituting the observation window and the observation cross section of the battery structure. If a deformable transparent filler is interposed between the transparent plate and the observation cross section, the recess formed by removing the active material is filled with the transparent filler, so that an electrolyte reservoir is formed. The problem is solved, and it becomes possible to observe a change in the state of the active material having a normal Li ion concentration in the surroundings.

The actual experimental results when charging is performed with a transparent filler interposed. That is, charging is started from a state where Li ions are not occluded. During a short time immediately after the start of charging, the color of the negative electrode active material in the entire region between the separator and the current collector foil was uniformly changed, and Li ions were uniformly intercalated. Thereafter, it was confirmed that the color change of the negative electrode active material closest to the separator progressed and Li ion intercalation progressed. Subsequently, the color of adjacent active materials changes sequentially, Li ions are intercalated, and Li ions are intercalated sequentially into the active material located closer to the current collector foil according to the charging time. confirmed. On the other hand, when an electrolyte pool was present between the transparent plate and the observation cross section, the color of the active material was uniformly changed almost simultaneously over the entire area. Therefore, when a transparent filler was interposed, it was confirmed that a state change almost corresponding to a state change in actual charge / discharge was observed.

In the present specification, the “deformable filler” includes not only a transparent filler that is deformable at room temperature, but also a filler that is deformed by preheating to a temperature exceeding the softening point. In addition, “optically transparent” means that there is no specific absorption or the like in the observation wavelength range, and there is no specific absorption in the ultraviolet to infrared wavelength range. Means optically transparent in the wavelength range from 400 nm to the near infrared region.

In a preferred embodiment of the method for observing a lithium ion battery according to the present invention, the filler is composed of an optically transparent thermoplastic resin,
Furthermore, the method includes a step of preheating a filler interposed between the transparent plate and the observation cross section,
The filler is deformed by the pre-heat treatment, and the concave space from which the active material in the observation cross section is removed is filled with the filler. Thermoplastic resins include a material whose softening temperature causing deformation is 80 ° C. or lower, which is the use limit temperature of battery materials. Therefore, a thermoplastic resin having a thickness of several μm to several tens of μm on the transparent plate constituting the observation window. Can be easily deformed by attaching a resin film and preheating using a heating means such as a hot plate, and a transparent resin layer can be interposed in the concave space formed between the separator and the current collector foil It is. Further, since the thermoplastic resin is cured by returning to normal temperature, it can be observed with a microscope in a state where the shape of the surface of the observation cross section is maintained.

As the transparent filler, a polyolefin-based thermoplastic resin can be used. As specific examples, an ethylene ethyl acrylate copolymer, an ethylene vinyl acetate copolymer, or an ultra-low density polyethylene can be used.

A test lithium ion battery according to the present invention is a test lithium ion battery used for a performance test,
A lithium ion battery structure including a positive electrode plate on which a positive electrode active material layer is formed, a negative electrode plate on which a negative electrode active material layer is formed, and a separator positioned between the positive electrode plate and the negative electrode plate;
An insulating case for storing the lithium ion battery structure;
A terminal electrically connected to each of the positive electrode plate and the negative electrode plate and located outside the insulating case;
A fixing jig for fixing the insulating case and the lithium ion battery structure housed in the insulating case;
A transparent plate coupled to a reference plane of the fixture and constituting an observation window;
The lithium ion battery structure is positioned so as to face the transparent plate and has an observation cross section on which illumination light for microscope observation is incident,
An optically transparent and deformable filler is filled between the transparent plate and the observation cross section of the lithium ion battery structure.

The method for producing a test lithium ion battery according to the present invention is a method for producing a test lithium ion battery used for a performance test,
A positive electrode plate on which a positive electrode active material layer is formed, a negative electrode plate on which a negative electrode active material layer is formed, a separator disposed between the positive electrode plate and the negative electrode plate, and each connected to the positive electrode plate and the negative electrode plate Preparing a lithium ion battery structure having a connected terminal;
Surrounding the periphery of the lithium ion battery structure with an insulating film, and fixing the lithium ion battery structure and the insulating film using a fixing jig;
An observation cross section forming step of cutting the lithium ion battery structure using the reference surface of the fixing jig to form an observation cross section for microscopic observation,
Removing the active material removed from the battery network by the observation cross-section forming process;
An observation window forming step of coupling a transparent plate constituting the observation window to the reference surface of the fixing jig;
A battery forming step of encapsulating an electrolytic solution in the internal space of the insulating film, forming an observation window and forming a sealed lithium ion battery that can be charged and discharged;
In the observation window forming step, a deformable optically transparent filler is interposed between the transparent plate and the observation cross section of the lithium ion battery structure.

  In the present invention, the active material removed from the battery network by the cutting process is removed from the observation cross section, and the recess formed in the observation cross section is filled with a deformable transparent filler, so that the electrolyte cross section is stored in the observation cross section. It is possible to observe the change in the state of the active material during the charge / discharge operation corresponding to an actual lithium ion battery.

It is a figure which shows a series of manufacturing processes of the lithium ion battery for a test by this invention. It is a figure which shows a series of manufacturing processes of the lithium ion battery for a test by this invention. It is a diagrammatic sectional view showing the structure near the observation window. It is a figure which shows the observation system which enforces the observation method of the lithium ion battery by this invention. It is a figure which shows an example of a flange. It is a figure which shows an example of a cell main body. It is a figure which shows the structure of a holding tool. It is a figure which shows the creation process of the lithium ion battery for a test. It is a diagrammatic sectional view showing a state near an observation section.

BEST MODE FOR CARRYING OUT THE INVENTION

  The method for observing a lithium ion battery according to the present invention creates a test lithium ion battery having a structure substantially similar to that of a lithium ion battery actually manufactured and sold in the market, and performs internal operations during repeated charging and discharging. The change in structure is observed from a direction parallel to the extending direction of the positive electrode plate and the negative electrode plate. A confocal microscope having a white light source is used as an observation means, and a color image of the observation area between the positive electrode plate and the negative electrode plate during the operation in which the electrochemical reaction proceeds is continuously or intermittently multiple times. Take an image. Then, a change in the color of the active material layer, a change in the particle size of the active material, generation of dendrites, and a growth state thereof are observed over time from the plurality of captured color images.

  First, a test lithium ion battery used for performance evaluation of a lithium ion battery and a method for manufacturing the same will be described. 1 and 2 are diagrams showing a series of manufacturing steps of a test lithium ion battery according to the present invention. Referring to FIG. 1A, a lithium ion battery structure 1 having basic components of a lithium ion battery is prepared. A lithium ion battery structure 1 includes a positive electrode plate 2 having a positive electrode active material layer formed on a current collector, a negative electrode plate 3 having a negative electrode active material layer formed on a current collector, a positive electrode plate, and a negative electrode It has the separator 4 arrange | positioned between board | substrates, and the terminal 5a and 5b for a connection connected to the positive electrode plate and the negative electrode plate. The positive electrode plate and the negative electrode plate are arranged so that the positive electrode active material layer and the negative electrode active material layer directly face the separator.

  For example, an aluminum foil is used as the current collector of the positive electrode plate 2, and a copper foil is used as the current collector of the negative electrode plate 3. As the positive electrode active material, lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, or a composite thereof is used. As the negative electrode active material, graphite, lithium titanate, Si compound or the like is used. As the separator 4, a porous body of a polyethylene compound or a polypropylene compound is used. The present invention is a test lithium ion battery for evaluating the performance of a lithium ion battery, and various performance evaluations are performed using various materials other than those described above as battery materials.

  As shown in FIG. 1B, the periphery of the lithium ion battery structure 1 is surrounded by an insulating film 6 constituting an insulating case. An insulating film can be comprised with the laminate film which can be heat-seal | fused, for example. One side end 6a of the insulating film 6 is sealed by heat sealing, and the other side end 6b is sealed so that the two connection terminals 5a and 5b are located outside. Therefore, the lithium ion battery structure 1 is enclosed in the case of the insulating film with the upper end 6c and the lower end 6d open.

  As shown in FIG. 1C, the upper end portion of the lithium ion battery structure 1 surrounded by the insulating film 6 is fixed together with the insulating film 6 by a fixing jig 10. The fixing jig 10 includes first and second fastening members 11 and 12 that are engaged with each other, and two fastening screws 13 a and 13 b that fasten and fix the fastening members 11 and 12. The two fastening members 11 and 12 form a space for sandwiching the lithium ion battery structure 1 covered with the insulating film when engaged. Further, a through hole is formed in the first fastening member 11 and a screw groove is formed in the second fastening member 12. A part of the lithium ion battery structure 1 and the insulating film 6 is sandwiched between the two fastening members 11 and 12, the fastening screws 13a and 13b are inserted into the through holes, and are screwed into the screw grooves to be lithium ion battery structures. The upper end portion of the substrate is fixed together with the insulating film. At this time, the upper portions of the lithium ion battery 1 and the insulating film 6 are projected upward.

  The upper side surfaces 11a and 12a of the two fastening members 11 and 12 are positioned so that the height level of the surface is the same level when engaged with each other, and the upper side surfaces 11a and 12a together are used for positioning. A reference surface 14 is formed. While fixing the glass plate which forms an observation window to this positioning reference plane 14, the reference plane 14 is used to define the positions of the edges of the lithium ion battery structure and the insulating film in the surface height direction. Grooves 11b and 12b for storing an adhesive for joining the glass plates are formed on the upper side surfaces 11a and 12a of the first and second fastening members, respectively. The grooves 11b and 12b are formed so as to surround the entire circumference at the upper end of the lithium ion battery. When the two fastening members of the fixing jig are engaged and fixed, they are hermetically fixed so that no gap is formed between the lithium ion battery structure 1 and the insulating film 6.

  The reference surface 14 constituted by the upper side surfaces 11a and 12a of the two fastening members 11 and 12 is used as a reference surface for cutting when forming an observation cross section. Then, for example, using a cutting tool (not shown) such as a razor or a microtome, the cutting tool is moved in the direction of the arrow a or b along the reference surface 14 and protrudes upward from the reference surface 14. The cutting process which cut | disconnects the edge part of a body and an insulating film is implemented. Thus, by cutting along the reference plane 14, an observation cross section (edge) for microscopic observation is formed, and the observation cross section is positioned at the same level with respect to the reference plane 14. The state after cutting is shown in FIG.

  After the cutting step, an active material removing step for partially removing the active material existing in the observation cross section and a filling step for filling the observation cross section with a filler are performed, and then an observation window is formed. The active material removal step and the filling step will be described later. In forming the observation window, the adhesive is introduced into the grooves 7b and 8b for storing the adhesive. As the adhesive, a transparent ultraviolet curable adhesive can be used. Thereafter, the glass plate 15 (transparent plate) is placed on the reference surface 14, irradiated with ultraviolet rays to cure the adhesive, and the glass plate 15 is positioned and fixed with respect to the reference surface 14 of the fixed tool 10. This state is shown in FIG. As the adhesive, various adhesives other than the ultraviolet curable adhesive can be used. For example, a transparent thermoplastic resin, a two-component adhesive, or a thermoplastic adhesive can be used.

  In the present invention, the upper part of the lithium ion battery and the insulating film is cut along the reference plane 14 to form an observation cross section, and then the active material that removes the active material that is disconnected from the adjacent active material A removal step is performed. When the present inventor observed the cut surface after mechanically cutting the lithium ion battery structure under a microscope, it was found that an active material deviated from the battery network was formed on the cut surface. That is, each active material is combined with an adjacent active material via a binder to form a network. On the other hand, when mechanically cutting using a cutting means such as a knife, the bond to the binder is broken on the surface of the cut surface, and the active material is not bonded to the adjacent active material, and an active material that is off the network is generated. Since such an active material does not perform charging / discharging action, when observing with a microscope, it becomes a shield against illumination light emitted from the microscope, and hinders observation with the microscope. Based on the result of this experiment, in this example, a step of removing the active material that is electrically disconnected by pressing the adhesive sheet against the cut surface is performed. By performing this active material removal treatment process, so-called live active materials (active materials connected to the battery network) exist mainly on the surface of the observation cross section, and each active material to be charged / discharged is charged. It becomes possible to image the state change.

On the other hand, when the active material present on the cut surface is partially removed, a concave space is formed in the cut surface. Therefore, when the electrolytic solution is subsequently sealed, a space in which the electrolytic solution exists excessively is formed between the glass plate and the observation cross section. On the other hand, when the electrolyte solution is present in excess around the active material, Li ions are excessively supplied to the active material being charged and discharged, resulting in a battery form different from a normal lithium ion battery. In order to eliminate such a problem, in the present invention, after removing the active material that has been removed from the network, the concave space formed in the observation cross section is filled with an optically transparent filler, and then the glass plate 15 is fixed. To do.

As the filler, an optimum material is selected based on optical properties, mechanical properties, chemical properties, and electrical properties. As optical characteristics, it is necessary to be transparent in the observation wavelength range, that is, not to have a specific absorption action in the observation wavelength range, and desirably not to have an absorption action in the wavelength range of 400 nm to the near infrared range. Moreover, as for the refractive index of the filler, it is desirable to use a material substantially equivalent to the refractive index of the electrolytic solution. That is, when the transparent filler is filled, the filler comes into contact with the electrolytic solution to form an interface. In this case, when the difference in refractive index between the transparent filler and the electrolytic solution is large, reflected light is generated at the interface, the interface image is superimposed on the image to be captured, and the image of the observed cross section is unclear. A problem occurs. The mechanical property is required to have a deformable property. That is, the deformation performance is required to enter the minute space between the separator and the current collector foil. In this case, a material that can be deformed under preheating conditions can be used together with a material that can be deformed at room temperature. For example, a film-like transparent filler or a gel-like transparent filler that can be deformed at room temperature or under preheating can be used. In particular, a thermoplastic resin that is deformed by preheating to a temperature equal to or higher than the softening point can be used. For example, a polyolefin-based thermoplastic resin is used. As a material that can be deformed at room temperature, if the clay is too high, it does not enter the concave space, and if the clay is too low, it enters the inside of the active material layer. Therefore, it is necessary to use an appropriate clay material. The range of suitable clay as filler is preferably in the range of 10 Pas to 1000 Pas. In addition, as a chemical characteristic, it is necessary to be a chemically inert material, and a material that does not react with the electrolytic solution is selected. In addition, it is necessary to have high insulation as electrical.

As a material that satisfies the above-described conditions, for example, an ethylene ethyl acrylate copolymer, an ethylene vinyl acetate copolymer, or ultra-low density polyethylene can be used. In particular, since the refractive index of the ethylene ethyl acrylate copolymer and the ethylene vinyl acetate copolymer has a small difference from the refractive index of the electrolytic solution, the problem that the captured image becomes unclear is prevented, and 400 nm to near red Since it does not have an absorbing action in the outer region, it is extremely effective.

In this example, the filler is filled into a concave space formed in the observation cross section using a thermoplastic resin that is deformed by preheating as the filler. That is, after forming an observation cross section in the cutting process, a thermoplastic film having a thickness of about several tens to several hundreds of μm is used as a filler, the thermoplastic resin film is mounted on a glass plate, and the glass plate is brought into contact with the hot plate To preheat to a temperature above the softening point of the thermoplastic resin. The thermoplastic resin film is softened by preheating and changes into a deformable state. Subsequently, the glass plate is fixed to the reference plane so that a deformable thermoplastic resin film is interposed between the glass plate 15 and the observation cross section. At this time, the softened thermoplastic resin enters the concave space of the observation cross section, and the concave space can be filled with the transparent filler. As another method, the thermoplastic film and the glass plate can be preheated after being fixed to the reference surface.

  2A and 2B show the manufacturing process after the observation window is formed. After the observation window is formed, a drying process is performed as necessary. FIG. 2A shows a state in which the fixed tool 10 is hermetically fixed to the lithium ion battery structure 1 and the insulating film, and after the glass plate 15 is joined to the fixed tool, the structure is arranged in the upside down direction. Indicates. In this state, both side ends 6a and 6b of the insulating film 6 are sealed, the upper end 6c is sealed by the fixing tool 10 and the glass plate 15, and only the lower end 6d is opened. This structure is placed in a pass box and vacuum dried. By this vacuum drying, moisture contained in the lithium ion battery structure is released to the outside of the insulating film through the open portion of the lower end 6d.

  After the vacuum drying process is completed, a non-active gas such as argon gas is sealed inside the pass box to set a non-active atmosphere. In this state, the electrolytic solution is sealed inside the insulating film using a dispenser.

  After encapsulating the electrolytic solution, charge / discharge is performed once as necessary to perform defoaming treatment. As the defoaming treatment, for example, the internal space of the pass box can be set to a vacuum atmosphere, and the gas generated in the vacuum atmosphere can be removed. The defoaming process is performed as necessary.

  After the defoaming process is completed, the lower end 6d of the insulating film is heat-sealed and hermetically sealed. This state is shown in FIG. In this way, a test lithium ion battery is completed which is sealed by the glass plate constituting the observation window, the fixed tool, and the insulating case made of the insulating film, and the connection terminals are located outside the insulating case. . The series of manufacturing steps described above are substantially the same as the actual manufacturing steps of a lithium ion battery, and thus a test lithium ion battery having a structure substantially similar to that of an actual product that is commercially available can be obtained.

  FIG. 3 shows a state near the observation window of the test lithium ion battery, and is a cross-sectional view taken along the line II in FIG. FIG. 3 (A) shows a test battery in which an electrolytic solution is sealed after removing the active material removed from the battery network, and FIG. 3 (B) shows the space between the transparent plate and the observation cross section after removing the active material. Shows a battery in which an optically transparent filler is filled, and then an electrolytic solution is sealed. In addition, the same code | symbol is attached | subjected to the component same as the component used in FIG.1 and FIG.2, and the description is abbreviate | omitted. As shown in FIG. 3A, when the active material removed from the battery network is removed, a concave shape in which no active material is partially present between the observation cross section 20 of the lithium ion battery structure and the transparent plate 15 is obtained. A space is formed. When the electrolytic solution is sealed in this state, an electrolytic solution reservoir 21 is formed between the surface of the observation cross section 20 and the glass plate 15. The electrolytic solution reservoir 21 is in a state where Li ions are excessively rich. That is, in the case of a normal battery, the electrolytic solution exists in the gap between the active materials, and the amount of the electrolytic solution present around each active material is very small. On the other hand, when an electrolytic solution pool is formed between the glass plate 15 and the observation cross section 21, a large amount of electrolytic solution exists around the active material existing on the surface of the observation cross section. There are excess Li ions. Furthermore, since Li ions are supplied from the positive electrode side through the separator 4 during charging, the active material present in the surface region of the observation cross section 20 is maintained in a state different from the normal state. When the observation cross section is observed in such a state, a problem of observing an active material in a state different from the actual active material occurs.

  On the other hand, as shown in FIG. 3 (B), the concave space formed between the cut surface of the battery structure and the glass plate 15 is filled with the transparent filler 22, and then the electrolyte is sealed. In this case, since the concave space is filled with the transparent filling, the electrolytic solution reservoir is not formed, and the periphery of the active material in the surface region of the observation cross section is covered with the electrolytic solution in an amount substantially equivalent to that of a normal battery. Furthermore, importantly, the problem that an excessive amount of Li ions is supplied via the separator 4 from the positive electrode side during charging is also solved.

  Next, an observation method for observing a change in state of the active material of the test lithium ion battery during charge / discharge will be described. FIG. 4 shows an observation system for performing the observation method of the lithium ion battery according to the present invention. In this example, a pot-type observation cell is used, a test lithium ion battery is accommodated in the observation cell, and the state change of the active material located in the observation cross section orthogonal to the positive electrode plate and the negative electrode plate is observed. First, a positive electrode plate, a negative electrode plate, and a separator are laminated and held by a holding tool in an inert atmosphere to form a lithium ion battery structure. Subsequently, the lithium ion battery structure is cut along the reference surface formed on the holding tool to form a cut surface, and further, the active material removed from the network existing on the cut surface is removed. Thereafter, the lithium ion battery structure is immersed in an electrolytic solution together with the holding tool, the holding tool is placed in the observation cell, and a sealed lithium ion battery for testing is created. Then, the observation cell containing the test lithium ion battery is placed on the stage of the microscope, connected to the charge / discharge controller via the connection terminal provided in the observation cell, and repeatedly charged and discharged. The change in the internal state of the lithium ion battery inside is observed with a microscope from a direction parallel to the extending direction of the positive electrode plate and the negative electrode plate. A confocal microscope is used for microscopic observation. Then, the confocal microscope captures images of the internal state of the lithium ion battery over time, and stores the captured image in the memory, thereby recording the shape change and color change of the active material and the dendrite generation state over time. can do.

  Referring to FIG. 4, the observation cell includes a cell main body 30 in which a test lithium ion battery to be observed is accommodated, and a flange 31 that is sealingly engaged with the cell main body. An observation window 32 including a transparent plate is formed on the flange 31, and the observation cross section of the test lithium ion battery arranged in the observation cell is observed through the observation window 32 through the microscope. That is, the illumination light emitted from the objective lens 33 of the microscope enters the inside of the observation cell through the transparent plate provided in the observation window 32, and illuminates the observation cross section (end face area) of the lithium ion battery observed. . Further, the reflected light emitted from the observation section is collected by the objective lens 33 of the microscope through the observation window. A confocal microscope is preferably used as the microscope. A confocal microscope can form an omnifocal image focused over a considerably wide range along the optical axis direction by capturing a plurality of two-dimensional images while moving the objective lens along the optical axis direction. it can. Therefore, it is possible to take a focused two-dimensional image and three-dimensional image of several active materials stacked along the optical axis direction of the observation cross section, and the color change of each active material due to charge / discharge And shape changes can be observed in real time. In particular, since the color of each active material changes according to the Li ion concentration contained in the active material, the distribution state of Li ions and the generation state of dendrite can be observed from the outside.

  The cell body 30 is provided with first and second connection terminals 34a and 34b in a state of being electrically insulated from surrounding members so as to face each other. These connection terminals are connected to the charge / discharge controller 35. The connection terminal is also electrically connected to the positive electrode plate and the negative electrode plate of the lithium ion battery disposed in the cell body inside the cell body. During the test of the lithium ion battery, a charge / discharge test is performed under the control of the charge / discharge controller 35 provided outside the observation cell, and the internal state of the lithium ion battery being charged / discharged changes the observation window. Through a microscope.

  5A and 5B are views showing an example of the flange, FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view taken along the line II-II in FIG. 5A. An observation window 32 is formed at the center of the flange 31. An optically transparent glass plate 36 having a thickness of about 1 mm is attached to the observation window via an adhesive. A deformable transparent filler layer 37 is formed on the glass plate 36. Alternatively, a deformable transparent film is attached. Illumination light emitted from the objective lens of the microscope enters the observation cross-sectional area of the lithium ion battery via the glass plate 36 and the transparent filler 37, and reflected light emitted from the observation cross-section passes through the transparent filler 37 and the glass plate 36. Then, it is condensed by the objective lens.

  6 is a diagram showing an example of a cell body in which a test lithium ion battery is housed, FIG. 6A is a schematic plan view seen from the flange side, and FIG. 6B is FIG. It is the II-II sectional view taken on the line of (A). As shown in FIG. 6A, the cell body 30 is provided with screw holes 38a and 38b into which screws for attaching the flange 31 are screwed, and positioning pins 39a and 39b. These two positioning pins define the relative positional relationship between the cell body and the flange. In addition, a ring-shaped groove is formed in the cell body, and an O-ring 40 is disposed in the ring-shaped groove, and the O-ring 40 forms a sealing engagement between the cell body and the flange.

  A circular recess 41 is formed in the cell body. A holding tool 43 for holding a test lithium ion battery 42 including a positive electrode plate, a negative electrode plate, and a separator is disposed in the recess 41. A second recess 44 is formed below the recess 41, and a spring 45 is disposed in the second recess. The spring 45 acts to press the holding tool 43 toward the observation window. Accordingly, the observation cross section of the lithium ion battery 42 observed by the microscope is pressed by the spring 45 in the observation window direction. With this pressing force, the observation cross section of the test lithium ion battery is pressed against the filler 37.

  Next, the operation of the holding tool for holding the test lithium ion battery will be described. FIG. 7 is a diagram showing a state in which the holding tool 43 is opened. The holding tool 43 includes a hinge 46 and first and second holding members 47 and 48 that can rotate around the hinge. The first and second holding members 47 and 48 are made of an electrically insulating synthetic resin material. A torsion spring 49 is attached to the hinge 46. The torsion spring 49 acts to press the first and second holding members against each other. Then, using this pressing force, the positive electrode plate, the negative electrode plate, and the separator are aligned and held to form a test lithium ion battery.

  First and second electrode plates 50 and 51 are provided on the mutually opposing surfaces of the first and second holding members 47 and 48, respectively. These electrode plates have the shape shown on the right side of FIG. 7, and have electrode plates 50a (51a) and lead portions 50b (51b). The electrode plates 50a and 51a are fixed to the surfaces of the holding members 47 and 48, respectively, and the lead portions 50b and 51b are first and second intermediate connection terminals located on the opposite surface through the inside (through hole) of the holding member. Spot welded to 52 and 53, respectively. Therefore, in a state where the lithium ion battery is held between the electrode plates of the holding tool, the current collector foil of the positive electrode plate and the current collector foil of the negative electrode plate of the lithium ion battery are intermediated via the electrode plates 49 and 50 of the holding tool. They are electrically connected to the connection terminals 51 and 52, respectively. As shown in FIG. 6B, the intermediate connection terminal is connected to the first and second connection terminals 34a and 34b, respectively. Accordingly, the positive and negative current collector foils of the test lithium ion battery are connected to the charge / discharge controller via the electrode plate and the intermediate connection terminal, respectively.

  Next, a process for producing a test lithium ion battery will be described. The positive electrode plate, the negative electrode plate, and the separator are stacked and sandwiched between the first holding member 47 and the second holding member 48 of the holding tool 43 to form a lithium ion battery structure. FIG. 8A shows a state in which the lithium ion battery structure 42 is sandwiched. The surface 47a of the first holding member 47 and the surface 48a of the second holding member 48 are set at the same height level, and these surfaces serve as a reference for forming a cut surface of the lithium ion battery structure. A surface. Next, the battery structure is cut by moving a cutting means such as a knife along the reference plane to form a cut surface orthogonal to the positive electrode plate and the negative electrode plate. Subsequently, the adhesive sheet is pressed against the cut surface, and the active material generated by the cutting process and removed from the network is removed. Thereby, the observation cross section 42a is formed. FIG. 8B shows a state after the cutting process.

  Thereafter, the holding tool is immersed in the electrolytic solution, the lithium ion battery structure is impregnated with the electrolytic solution, and then stored in the cell body. The holding tool is stored in the cell body, and then the flange is coupled to the cell body. This state is shown in FIG. As shown in FIG. 6, since the holding tool 43 receives a pressing force in a direction approaching the observation window by the spring 45, the film-like deformable filler 37 attached to the glass plate 36 enters the recess in the observation cross section. To do. As a result, the transparent filler 37 is filled into the concave space from which the active material in the observation cross section is removed. Thereby, the malfunction that a layer electrolyte pool is formed is eliminated. In this example, a film of a transparent filler that can be deformed is mounted on the glass plate 36, but after removing the active material, a liquid filler having a relatively high viscosity is applied to the concave space of the observation cross section, and then the flange is applied. May be combined.

DESCRIPTION OF SYMBOLS 1 Lithium ion battery structure 2 Positive electrode plate 3 Negative electrode plate 4 Separator 5a, 5b Terminal
6 Insulation film
DESCRIPTION OF SYMBOLS 10 Fixing jigs 11 and 12 Fastening member 14 Reference | standard surface 15 Glass plate 20 Observation cross section 21 Electrolyte reservoir 22 Transparent filler 30 Cell main body 31 Flange 32 Observation window 33 Objective lens 34a, 34b Connection terminal 35 Charge / discharge controller 36 Glass plate 37 Transparent filler

The observation method of a lithium ion battery according to the present invention is an observation method of a lithium ion battery in which an observation cross section orthogonal to the positive electrode plate and the negative electrode plate of a test lithium ion battery having a positive electrode plate, a negative electrode plate, and a separator is observed with a microscope. And
A step of preparing an observation cell having a cell main body for storing a holding tool for holding a test lithium ion battery, an observation window including a transparent plate, and a flange for sealing engagement with the cell main body;
An observation cross-section forming step of cutting a test lithium ion battery along a reference plane provided on the holding tool and forming an observation cross-section orthogonal to the positive electrode plate and the negative electrode plate;
Removing the active material removed from the battery network by the cutting process;
Impregnating the test lithium ion battery with an electrolytic solution , and storing the cell in the cell body such that the observation cross section faces the transparent plate;
Interposing an optically transparent and deformable thermoplastic resin filler between the observation cross section and the transparent plate;
Softening the filler by pre-heat treatment, and filling the concave space from which the active material of the observation cross section has been removed with the softened filler;
Projecting illumination light through the transparent plate and the filler constituting the observation window toward the observation cross section of the lithium ion battery structure, and capturing an image of the observation cross section of the lithium ion battery structure,
The surface of the filler facing the observation cross section is deformed along the end face shape of the active material layer in the observation cross section, and no excess electrolyte exists in the observation cross section .

The method for producing a test lithium ion battery according to the present invention is a method for producing a test lithium ion battery used for a performance test,
A positive electrode plate on which a positive electrode active material layer is formed, a negative electrode plate on which a negative electrode active material layer is formed, a separator disposed between the positive electrode plate and the negative electrode plate, and each connected to the positive electrode plate and the negative electrode plate Preparing a lithium ion battery structure having a connected terminal;
Surrounding the periphery of the lithium ion battery structure with an insulating film, and fixing the lithium ion battery structure and the insulating film using a fixing jig;
An observation cross section forming step of cutting the lithium ion battery structure using the reference surface of the fixing jig to form an observation cross section for microscopic observation,
Removing the active material removed from the battery network by the cutting process ;
An observation window forming step of coupling a transparent plate constituting the observation window to the reference surface of the fixing jig;
A battery forming step of encapsulating an electrolytic solution in the internal space of the insulating film to form a sealed lithium ion battery that can be charged and discharged;
The observation window forming step includes a step of interposing an optically transparent thermoplastic resin filler between the transparent plate and the observation cross section of the lithium ion battery structure , and softening the filler by preheat treatment. ,
The concave space from which the active material in the observation cross section is removed is filled with a softened filler .

Claims (12)

A method for observing a lithium ion battery by microscopically observing a cross section perpendicular to a positive electrode plate and a negative electrode plate of a test lithium ion battery having a positive electrode plate, a negative electrode plate, and a separator,
A step of preparing an observation cell having a cell main body for storing a holding tool for holding a test lithium ion battery, an observation window including a transparent plate, and a flange for sealing engagement with the cell main body;
An observation cross-section forming step of cutting a test lithium ion battery along a reference plane provided on the holding tool and forming an observation cross-section orthogonal to the positive electrode plate and the negative electrode plate;
Removing the active material removed from the battery network by the cutting process;
Storing the test lithium ion battery in the cell body such that the observation cross section faces the transparent plate;
Filling an optically transparent and deformable filler between the observation cross section and the transparent plate;
Projecting illumination light through the transparent plate and the filler constituting the observation window toward the observation cross section of the lithium ion battery structure, and capturing an image of the observation cross section of the lithium ion battery structure. A method for observing a lithium ion battery characterized by the above.   2. The observation method for a lithium ion battery according to claim 1, wherein the positive electrode plate and the negative electrode plate of the test lithium ion battery are connected to a charge / discharge controller, and an image of an observation cross section during charge / discharge is taken. A method for observing a lithium ion battery. The observation method of a lithium ion battery according to claim 1 or 2, wherein the filler is composed of an optically transparent thermoplastic resin,
Furthermore, the method includes a step of preheating a filler interposed between the transparent plate and the observation cross section,
A method for observing a lithium ion battery, wherein the filler is deformed by pre-heat treatment, and the concave space from which the active material in the observation cross section is removed is filled with the filler.   4. The observation method for a lithium ion battery according to claim 3, wherein a spring that presses the holding tool so as to approach an observation window provided on a flange is disposed in the cell body, and the preheating is performed by a pressing force of the spring. A method for observing a lithium ion battery, wherein the filler is filled in the space from which the active material has been removed.   5. The observation method for a lithium ion battery according to claim 4, wherein a surface of the preheated filler facing the observation cross section is deformed along an end face shape of the active material layer of the observation cross section, and excess electrolysis is observed in the observation cross section. A method for observing a lithium ion battery, characterized in that no liquid is present.   A microscope used for carrying out the method for observing a lithium ion battery according to claim 1. A lithium ion battery for testing used for performance testing,
A lithium ion battery structure including a positive electrode plate on which a positive electrode active material layer is formed, a negative electrode plate on which a negative electrode active material layer is formed, and a separator positioned between the positive electrode plate and the negative electrode plate;
An insulating case for storing the lithium ion battery structure;
A terminal electrically connected to each of the positive electrode plate and the negative electrode plate and located outside the insulating case;
A fixing jig for fixing the insulating case and the lithium ion battery structure housed in the insulating case;
A transparent plate coupled to a reference plane of the fixture and constituting an observation window;
The lithium ion battery structure is positioned so as to face the transparent plate and has an observation cross section on which illumination light for microscope observation is incident,
An optically transparent and deformable filler is filled between the transparent plate and the observation cross section of the lithium ion battery structure.   8. The test lithium ion battery according to claim 7, wherein a thermoplastic resin that is optically transparent and can be deformed by a preheat treatment is used as the filler. .   9. The test lithium ion battery according to claim 8, wherein a polyolefin-based thermoplastic resin is used as the filler.   The lithium ion battery according to claim 9, wherein the filler is selected from an ethylene ethyl acrylate copolymer, an ethylene vinyl acetate copolymer, or an ultra-low density polyethylene. A method for producing a test lithium ion battery used in a performance test,
A positive electrode plate on which a positive electrode active material layer is formed, a negative electrode plate on which a negative electrode active material layer is formed, a separator disposed between the positive electrode plate and the negative electrode plate, and each connected to the positive electrode plate and the negative electrode plate Preparing a lithium ion battery structure having a connected terminal;
Surrounding the periphery of the lithium ion battery structure with an insulating film, and fixing the lithium ion battery structure and the insulating film using a fixing jig;
An observation cross section forming step of cutting the lithium ion battery structure using the reference surface of the fixing jig to form an observation cross section for microscopic observation,
Removing the active material removed from the battery network by the observation cross-section forming process;
An observation window forming step of coupling a transparent plate constituting the observation window to the reference surface of the fixing jig;
A battery forming step of encapsulating an electrolytic solution in the internal space of the insulating film, forming an observation window and forming a sealed lithium ion battery that can be charged and discharged;
In the observation window forming step, an optically transparent filler is interposed between the transparent plate and the observation cross section of the lithium ion battery structure. 12. The method for producing a test lithium ion battery according to claim 11, wherein a thermoplastic resin is used as the filler, and includes a step of preheating the filler in the observation window forming step, and the filling by preheat treatment. A method for producing a test lithium ion battery, wherein the agent is softened and the concave space from which the active material in the observation cross section is removed is filled with the filler.

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