JP2013062139A - Evaluation method of electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method which promptly and easily evaluates segregation of a binding material in an electrode mixture layer without relying on a troublesome means investigating a distribution of the binding material in the electrode mixture layer.SOLUTION: An evaluation method of an electrode comprises the steps of: measuring an interfacial peeling strength A of an interface between an electrode current collector 82A and an electrode mixture layer 90A of an electrode 84A as an evaluation object by peeling the electrode mixture layer from the electrode current collector; measuring a film strength B including the interfacial peeling strength of the interface between the electrode current collector and the electrode mixture layer and a breaking strength of the electrode mixture layer, by peeling a part of the electrode mixture layer of the electrode as the evaluation object from the electrode current collector in such a manner that the part of the electrode mixture layer is torn off from the surrounding part thereof; and obtaining an intensity ratio A/B of the interfacial peeling strength A and the film strength B and estimating segregation degree of a binding material in the electrode mixture layer as the evaluation object on the basis of the intensity ratio A/B.

Description

  The present invention relates to a method for evaluating an electrode provided in a lithium ion secondary battery or other battery, and relates to a method for evaluating an electrode including a binder.

  Lithium-ion secondary batteries, nickel-metal hydride batteries, and other batteries (typically secondary batteries) are used, for example, as power sources mounted on vehicles that use electricity as a drive source, personal computers, portable terminals, and other electrical products. The importance is increasing as a power source to be used. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferable as a high-output power source mounted on a vehicle.

In a lithium ion secondary battery having a typical configuration, an electrode material mainly composed of a substance (electrode active material) capable of reversibly occluding and releasing lithium ions on a conductive member (electrode current collector) is layered. An electrode having a formed configuration (hereinafter, this layered product is referred to as an “electrode mixture layer”) is provided. In such an electrode, typically, a paste-like composition in which an electrode active material and a binder (binder) are dispersed in a suitable solvent (for example, water) and kneaded (a slurry-like composition is included in the paste-like composition). And an ink-like composition are prepared, and this is coated on an electrode current collector and dried to form an electrode mixture layer on the current collector.
Here, sufficient peeling strength is provided between the electrode current collector and the electrode mixture layer so that the electrode mixture layer does not peel off from the electrode current collector during battery assembly or charge / discharge. (Adhesion) is required. Patent documents 1 to 4 are mentioned as conventional technology about measurement of peel strength (adhesion power) between an electrode compound material layer and an electrode current collector.

JP 2008-287936 A JP 2010-211975 A JP 2008-103098 A JP 2006-107780 A

By the way, when the electrode mixture layer is formed by drying the paste-like composition applied on the electrode current collector, the solvent in the composition evaporates from the surface of the composition. The binder contained in the composition may move and segregate (migrate) on the surface of the composition. When the binder is segregated on the surface side of the electrode mixture layer, the strength on the surface side of the electrode mixture layer becomes higher than the strength on the current collector side. Therefore, even when a sufficient peel strength is observed between the electrode mixture layer and the electrode current collector, the strength of the electrode mixture layer is weaker when an external force is applied to the electrode mixture layer. There is a possibility that the electrode mixture layer may be peeled off from the electrode current collector side which is a part. Therefore, it is important to correctly grasp the difficulty of peeling of the electrode mixture layer from the electrode current collector (that is, peel strength) in the battery to be manufactured. In this regard, it is not sufficient to measure the peel strength between the electrode mixture layer and the electrode current collector. That is, the peel strength is affected by the distribution of the binder in the electrode mixture layer (presence / absence of segregation of the binder).
Here, in the technique described in Patent Document 1, the distribution of the binding material is evaluated by dyeing the binding material in the electrode mixture layer with osmic acid. There was a problem of requiring time and money. As another conventional technique, there is a method for evaluating the distribution of the binder by dyeing the binder in the electrode mixture layer with bromine. However, this method has the same problems as the above method and is used. Some binders cannot be dyed, and in such cases, the distribution of the binder could not be evaluated.

  Therefore, the present invention has been created to solve the above-described conventional problems, and the purpose thereof is to use a complicated means such as bromine dyeing for the distribution of the binder in the electrode mixture layer. It is to provide a method for quickly and easily evaluating the degree of segregation of the binder in the electrode mixture layer.

  In order to achieve the above object, according to the present invention, an electrode mixture layer containing at least an electrode active material and a binder is formed on the electrode current collector. A method for assessing segregation is provided. That is, the electrode evaluation method disclosed here is an interface between the electrode current collector and the electrode mixture layer by peeling the electrode mixture layer of the electrode to be evaluated from the electrode current collector. Measuring the interfacial peel strength A, and breaking the electrode composite material layer of the electrode to be evaluated from the electrode composite material layer around the electrode current collector layer. By measuring the film strength B including the interfacial peel strength at the interface between the electrode current collector and the electrode composite layer and the breaking strength of the electrode composite layer by peeling from the body, the interfacial peel strength A And calculating a strength ratio A / B between the film strength B and estimating the degree of segregation of the binder in the electrode composite layer as the evaluation target from the strength ratio A / B. It is characterized by.

In the electrode evaluation method of the present invention, the interfacial peel strength A at the interface between the electrode current collector and the electrode mixture layer is measured, and the breaking strength of the electrode mixture layer (that is, the film in the thickness direction of the electrode mixture layer) Film strength B including (strength) is measured, and the strength ratio A / B is obtained.
The breaking strength in the film strength B is affected by the distribution of the binder in the electrode mixture layer (that is, the binder is partially concentrated in the electrode mixture layer (segregated). ), The breaking strength in the portion is larger than that in the case where the binder is well dispersed throughout the electrode composite layer. The degree of segregation of the binder in the composite layer can be evaluated by measuring the strength B and obtaining the strength ratio A / B.

In a preferred aspect of the evaluation method disclosed herein, when the intensity ratio A / B is equal to or greater than a predetermined value, it is determined as a non-defective product, and when the intensity ratio A / B is smaller than the predetermined value. Is further characterized in that it is judged as a defective product.
When the strength ratio A / B is equal to or greater than a predetermined value (depending on the target battery structure, the material used, etc.), the binder is well dispersed in the electrode mixture layer and the electrode mixture It is judged that the difference in strength between the interfacial peel strength and the breaking strength between the layer and the electrode current collector is small. That is, an electrode that satisfies the above conditions can be an electrode that has a sufficient adhesion between the electrode current collector and the electrode mixture layer and has an appropriate breaking strength, so that it is difficult to peel off.

In another preferred embodiment of the evaluation method disclosed herein, the interfacial peel strength A is determined by removing the electrode mixture layer from the electrode current collector at a peel angle of 90 degrees from the edge of the electrode mixture layer. The film strength B is measured by peeling, and the film strength B is a portion of the electrode mixture layer around the electrode mixture layer at a peel strength of 90 degrees from the central portion excluding the edge of the electrode mixture layer. It is characterized by measuring by peeling from the electrode current collector in such a way that it is broken (torn) from the layer.
According to such a configuration, the interfacial peel strength A and the film strength B can be measured quickly and easily.

In another preferred aspect of the evaluation method disclosed herein, the interfacial peel strength A is obtained by cutting a part of the electrode composite layer from the other part of the electrode composite layer in advance and a peel angle of 180. Measured by peeling a part of the electrode mixture layer from the electrode current collector, and the film strength B is 180 degrees peel strength from the central portion excluding the edge of the electrode mixture layer. The method is characterized in that a part of the electrode mixture layer is peeled off from the electrode mixture layer around the electrode mixture layer and peeled off from the electrode current collector.
According to such a configuration, the interfacial peel strength A and the film strength B can be measured in a shorter time.

In another preferred embodiment of the evaluation method disclosed herein, when measuring the interface strength A and the film strength B, an adhesive tape is applied in advance to the surface of the peeled portion of the electrode mixture layer. It is characterized by leaving.
According to this configuration, when the strength is measured, the electrode mixture layer is peeled off from the electrode current collector together with the adhesive tape, so that it is possible to prevent a problem that an unintended portion of the electrode mixture layer is broken. The electrode mixture layer can be easily peeled off.

It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment. It is sectional drawing which follows the II-II line | wire in FIG. It is a perspective view which shows typically the structure of the apparatus which measures the interface peeling strength A in the evaluation method of the electrode which concerns on one Embodiment of this invention. It is a perspective view which expands and shows a part of Drawing 3A. It is a perspective view which shows typically the structure of the apparatus which measures the film | membrane intensity | strength B in the evaluation method of the electrode which concerns on one Embodiment of this invention. It is a perspective view which expands and shows a part of Drawing 4A. It is a perspective view which shows typically the structure of the apparatus which measures the interface peeling strength A in the evaluation method of the electrode which concerns on other one Embodiment of this invention. It is sectional drawing which follows the 5B-5B line | wire in FIG. 5A. It is sectional drawing which shows typically the state which peeled the electrode compound-material layer from the electrode electrical power collector. It is a perspective view which shows typically the structure of the apparatus which measures the film | membrane intensity | strength B in the evaluation method of the electrode which concerns on other one Embodiment of this invention. It is sectional drawing which follows the 6B-6B line | wire in FIG. 6A. It is sectional drawing which shows typically the state which peeled the electrode compound-material layer from the electrode electrical power collector. It is a cross-sectional SEM image which shows the state of the negative mix layer which concerns on Example 1 after a bromine dyeing | staining. It is a cross-sectional SEM image which shows the state of the negative mix layer which concerns on Example 2 after a bromine dyeing | staining.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  In the electrode evaluation method disclosed herein, the interfacial peel strength A and the film strength B of the electrode to be evaluated are measured, and the binding ratio in the electrode mixture layer is determined from the strength ratio A / B. Includes estimating the degree of segregation.

  Hereinafter, a preferred example (first embodiment) that can be adopted to obtain the interfacial peel strength A and film strength B will be described with reference to FIGS. 3A to 4B. In the following description, as described as an electrode, the present invention can be applied to either a positive electrode or a negative electrode. That is, when the following description is applied to the positive electrode, the electrode in the following description can be read as the positive electrode, and when applied to the negative electrode, it can be read as the negative electrode. As a preferred embodiment, the evaluation method of the present invention can be applied to a negative electrode for a lithium ion secondary battery including a binder that is relatively segregated, such as styrene butadiene rubber (SBR).

  As shown in FIG. 3A and FIG. 4A, the 90-degree peel strength measuring instrument 110 according to the present embodiment roughly includes a mounting table 120 on which an electrode 84 (84A) to be evaluated is mounted, and an electrode 84 ( 84A) and a tension jig (for example, clamp) 130 for fixing the electrode mixture layer 90 (90A). The tension jig 130 can adjust the tension speed and is configured to be movable up and down in the vertical direction (directions of arrows X1 and X2 in FIGS. 3A and 4A) with respect to the mounting table 120. Further, the tension jig 130 is provided with a measuring instrument 140 capable of measuring the peeling force when peeling the electrode mixture layer 90 (90A) from the electrode current collector 82 (82A). The mounting table 120 is configured to be movable in the horizontal direction (the directions of arrows Y1 and Y2 in FIGS. 3A and 4A). When the electrode mixture layer 90 (90A) is peeled from the electrode current collector 82 (82A) (so as to break), the interface between the electrode mixture layer 90 (90A) and the electrode current collector 82 (82A) is The tension jig 130 and the mounting table 120 are moved in conjunction with each other so as to be always maintained at an angle of 90 degrees (peeling angle) with respect to the movement direction of the tension jig 130 (the direction of the arrow X1 in FIGS. 3A and 4A). To do. The tension jig 130 and the mounting table 120 are connected by a cord 150, and the cord 150 moves the vertical direction of the tension jig 130 (in the direction of arrow X1 in FIGS. 3A and 4A) and the horizontal movement of the mounting table 120. (The direction of the arrow Y1 in FIGS. 3A and 4A) is interlocked, and the peeling angle is kept constant at 90 degrees.

First, a method for measuring the interfacial peel strength A will be described.
As shown in FIG. 3A, the electrode 84 to be evaluated is mounted on the mounting table 120. At this time, the electrode 84 is fixed to the mounting table 120 via the double-sided adhesive tape 160 so that the electrode 84 does not move from the mounting table 120. The electrode 84 fixed to the mounting table 120 may be cut out to an appropriate size as necessary.
As shown in FIG. 3A, in any one of the electrode mixture layers 90 formed on both surfaces of the long electrode current collector 82, an electrode having a predetermined length is formed from one edge of the electrode mixture layer 90. The composite material layer 90 is peeled from the electrode current collector 82. At this time, in order to measure the interfacial peel strength A at the interface between the electrode mixture layer 90 and the electrode current collector 82, as shown in FIG. The entire width direction (that is, in a state where a part of the electrode mixture layer 90 is not broken) is peeled off from the electrode current collector 82. Then, the peeled portions of the electrode mixture layer 90 and the electrode current collector 82 are fixed to the tension jig 130.
By raising the tension jig 130 in the vertical direction (the direction of the arrow X1 in FIG. 3A), the mounting table 120 is also moved in the horizontal direction (the direction of the arrow Y1 in FIG. 3A) via the cord 150, and the peeling angle is maintained at 90 degrees. In this state, the electrode mixture layer 90 is peeled from the electrode current collector 82. The peeling force measured by the measuring instrument 140 at this time is the interface peeling strength A at the interface between the electrode mixture layer 90 and the electrode current collector 82 as shown in FIG. 3B. In this way, the interfacial peel strength A is measured.
In the example shown in FIG. 3A, the lower electrode mixture layer 90 is peeled off from the electrode current collector 82, but the upper electrode mixture layer 90 may be peeled off from the electrode current collector 82. In this case, the upper electrode current collector 90 is fixed to the tension jig 130 and the interfacial peel strength A is measured, but the upper electrode current mixture layer 90 is not broken at an unintended portion during the measurement. It is preferable to attach an adhesive tape to the surface of the material layer 90.

Next, a method for measuring the film strength B will be described.
As shown in FIG. 4A, an electrode 84A having a longer length in the width direction than the electrode 84 used when the interfacial peel strength A is measured is placed on a mounting table 120 via a double-sided adhesive tape 160. It should be noted that the electrodes 84 and 84A are the same in material and composition ratio used only in size.
In either one of the electrode mixture layers 90A formed on both surfaces of the long electrode current collector 82A, the length in the width direction is the same as that of the electrode mixture layer 90 when the interfacial peel strength A is measured. A part of the electrode mixture layer 90A is peeled off from the electrode current collector 82A. More specifically, a part of the electrode mixture layer 90A is broken from the surrounding electrode mixture layer 90A by a predetermined length from the central portion excluding the edge of the electrode mixture layer 90A (torn off). And so on) from the electrode current collector 82A. Then, the peeled portion of the electrode mixture layer 90 </ b> A is fixed to the tension jig 130. When measuring the film strength B, an adhesive tape 170 is attached to the surface of the electrode mixture layer 90A to be peeled so that the peeled electrode mixture layer 90A is not broken (not torn) in the middle. It is preferable to fix the electrode mixture layer 90 </ b> A and the adhesive tape 170 to the tension jig 130.
By raising the tension jig 130 in the vertical direction (in the direction of arrow X1 in FIG. 4A), the mounting table 120 is also moved in the horizontal direction (in the direction of arrow Y1 in FIG. 4A) via the cord 150, and the peeling angle is maintained at 90 degrees. In this state, a part of the electrode mixture layer 90A is peeled from the electrode current collector 82A so as to break from the surrounding electrode mixture layer 90A. As shown in FIG. 4B, the peel force measured by the measuring instrument 140 at this time is the interface peel strength at the interface between the electrode mixture layer 90A and the electrode current collector 82A and the breaking strength of the electrode mixture layer 90A (ie, The film strength B includes the strength in the thickness direction of the electrode mixture layer 90A. In this way, the film strength B is measured.

By obtaining the strength ratio A / B between the interfacial peel strength A and the membrane strength B measured by the above method, the electrode composite layer 90 (of the electrode 84 (84A) to be evaluated is obtained from the strength ratio A / B. The degree of segregation of the binder in 90A) can be estimated. The breaking strength of the electrode mixture layer included in the film strength B is affected by the distribution of the binder in the electrode mixture layer.
In general, the binder in the electrode mixture layer is required to be uniformly distributed (dispersed). In order to evaluate the binder, it is desirable that the value of the strength ratio A / B is close to 1. When the binder in the electrode mixture layer is well dispersed, the breaking strength of the electrode mixture layer can be substantially the same throughout the thickness direction. That is, since the binder is not partially unevenly distributed, the breaking strength does not increase locally, and the value of the strength ratio A / B approaches 1. On the other hand, when the binder in the electrode mixture layer is segregated, the fracture strength is locally increased because the binder is partially distributed, and the value of the strength ratio A / B is Approaching zero.
Preferably, in the electrode evaluation method disclosed herein, when the intensity ratio A / B is equal to or greater than a predetermined value, the electrode is judged as non-defective, and when the intensity ratio A / B is smaller than the predetermined value. Further includes determining a defective product. Here, the predetermined value varies depending on the structure of the target battery, the material used, and the like, and can be set as appropriate according to the desired battery.

  The electrode evaluation method disclosed here does not need to investigate the distribution of the binder in the electrode mixture layer using a complicated means such as bromine dyeing as in the prior art. By measuring the interfacial peel strength A and the film strength B, the degree of segregation of the binder in the electrode mixture layer can be estimated quickly and easily. Furthermore, even if the material cannot be dyed depending on the type of the binder, the degree of segregation of the binder in the electrode mixture layer can be estimated according to the evaluation method.

  The electrode evaluation method disclosed herein can be incorporated into, for example, an electrode manufacturing method (and thus a battery manufacturing method). Hereinafter, as one of preferred embodiments of the method for producing an electrode disclosed herein, an electrode (negative electrode) for a lithium ion secondary battery in which an electrode mixture layer is formed on the surface of an electrode current collector is produced. The method will be described as an example, but the present invention is not intended to be limited to such batteries and electrodes.

The manufacturing method of the electrode (negative electrode) for lithium ion secondary batteries disclosed here includes a composition coating step, an electrode mixture layer forming step, and an electrode evaluation step.
First, the composition application process will be described. In the composition coating step, a paste-like composition containing at least a negative electrode active material (electrode active material) and a binder is prepared, and the prepared composition is used as a negative electrode current collector (electrode current collector). Application on the body).

  Examples of the negative electrode active material (electrode active material) used for the negative electrode of the lithium ion secondary battery disclosed herein include carbon-based materials such as graphite carbon and amorphous carbon, and lithium transition metal composite oxide (lithium titanium composite oxide). Etc.). Among them, the use of a negative electrode active material (typically, a negative electrode active material substantially made of natural graphite (or artificial graphite)) containing natural graphite (or artificial graphite) as a main component is preferable.

The binder used for the negative electrode of the lithium ion secondary battery disclosed herein (that is, the binder used for the composition) is used for the negative electrode of a general lithium ion secondary battery. The binder can be appropriately employed. For example, when a composition containing an aqueous solvent is used to form the negative electrode mixture layer, styrene butadiene rubber (SBR), polyacrylate (acrylic ester homopolymer or copolymer), and the like can be given.
Moreover, the negative electrode of the lithium ion secondary battery disclosed here can contain a thickener as needed. Examples of the thickening material include carboxymethyl cellulose (CMC) and methyl cellulose (MC).

  The operation of mixing (kneading) the negative electrode active material, the binder and the thickener in a solvent is performed using, for example, a suitable kneader (planetary mixer, homodisper, clear mix, fill mix, etc.). be able to. Although not particularly limited, in order to improve the drying efficiency, the solid content concentration of the composition (nonvolatile content, that is, the proportion of the negative electrode mixture layer forming component) is, for example, about 45% by mass or more (typically 50%). ˜80 mass%). If the solid content concentration is too smaller than the above range, the composition may be repelled on the negative electrode current collector and may not be applied to a uniform thickness. On the other hand, when the solid content concentration is too larger than the above range, the handleability of the composition (for example, coating properties when the composition is applied to a negative electrode current collector (particularly a foil-shaped current collector)) decreases. May be easier.

  As the negative electrode current collector, a conductive member made of a metal having good conductivity is preferably used, like the current collector used in the negative electrode of a conventional lithium ion secondary battery. For example, a copper material, a nickel material, or an alloy material mainly composed of them can be used. The shape of the negative electrode current collector can vary depending on the shape of the lithium ion secondary battery, and is not particularly limited.

Next, the electrode (negative electrode) composite material layer forming step will be described. In the electrode mixture layer forming step, the composition applied on the electrode current collector (negative electrode current collector) is dried on an electrode current collector (negative electrode current collector) by drying with an appropriate drying means. Forming a layer (negative electrode composite material layer).
For example, such a composition can be dried by passing a negative electrode current collector coated with the composition through a drying furnace. The drying temperature at this time is, for example, about 50 ° C. to 200 ° C. (for example, about 60 ° C. to 160 ° C.). The drying time is, for example, about 10 seconds to 120 seconds (for example, about 20 seconds to 60 seconds). By removing the solvent from the composition, a negative electrode mixture layer is formed on the negative electrode current collector. Then, it compresses (presses) as needed. Thereby, a negative electrode provided with a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector can be produced. As a compression (press) method, a conventionally known compression method such as a roll press method or a flat plate press method can be employed.

Next, an electrode (negative electrode) evaluation process will be described. In the electrode evaluation step, a part of the electrode (negative electrode) produced as described above is used as an evaluation target electrode, and the above-described electrode evaluation method is used. That is, for the electrode to be evaluated, the interface peel strength A and the film strength B are measured to determine the strength ratio A / B. Then, the strength ratio A / B is compared with a predetermined value X (X can be arbitrarily determined according to the structure of the battery, etc.), and the strength ratio A / B is a value X. In the above case, the manufactured electrode is determined as a non-defective product, and when it is smaller than the value X, the manufactured electrode is determined as a defective product.
In addition, as a method of adjusting the strength ratio A / B to a predetermined value X or more, for example, the type of the binder used in the composition coating step, the particle size, the content rate change, the electrode mixture layer forming step Examples of the method include changing the drying conditions (for example, drying temperature and drying time) of the composition.

  Hereinafter, an embodiment of a lithium ion secondary battery constructed using a negative electrode determined to be a non-defective product by the above manufacturing method will be described with reference to the drawings. However, the present invention is intended to be limited to the embodiment. is not. In the following embodiment, a lithium ion secondary battery having a configuration in which a wound electrode body and an electrolytic solution are housed in a rectangular battery case will be described as an example.

FIG. 1 is a perspective view schematically showing a lithium ion secondary battery 10 according to the present embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG.
As shown in FIG. 1, the lithium ion secondary battery 10 according to this embodiment includes a battery case 15 made of metal (a resin or a laminate film is also suitable). The case (outer container) 15 includes a flat cuboid case main body 30 having an open upper end, and a lid body 25 that closes the opening 20. The lid body 25 seals the opening 20 of the case main body 30 by welding or the like. The upper surface of the case 15 (that is, the lid body 25) is electrically connected to the positive electrode terminal 60 electrically connected to the positive electrode (positive electrode sheet) 64 of the wound electrode body 50 and the negative electrode (negative electrode sheet) 74 of the electrode body. A negative electrode terminal 70 is provided. In addition, the lid 25 is provided with a safety valve 40 for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal, as in the case of the conventional lithium ion secondary battery. . Inside the case 15, the positive electrode sheet 64 and the negative electrode sheet 74 are laminated together with a total of two separator sheets 95 and wound, and then the obtained wound body is crushed from the side direction and ablated. A flat wound electrode body 50 and an electrolyte (for example, a non-aqueous electrolyte) are accommodated.

The positive electrode active material used in the positive electrode (positive electrode sheet) 64 of the lithium ion secondary battery disclosed herein is a material capable of occluding and releasing lithium ions, and includes lithium element and one or more transition metals. Examples thereof include lithium-containing compounds containing elements (for example, lithium transition metal composite oxides). For example, lithium nickel composite oxide (for example, LiNiO ₂ ), lithium cobalt composite oxide (for example, LiCoO ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ ), or lithium nickel cobalt manganese composite oxide (for example, LiNi _1). Ternary lithium-containing composite oxide such as _{/ 3} Co _1/3 Mn _1/3 O ₂ ).

  As the conductive material, for example, a carbon material such as carbon powder or carbon fiber can be used. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black, etc.), carbon powders such as graphite powder can be used.

  Further, as the binder (binder), the same binder as that used for the positive electrode of a general lithium ion secondary battery can be appropriately employed. When preparing a composition using an aqueous solvent, what is used for the said negative electrode can be employ | adopted suitably. When preparing a composition using a solvent-based solvent, a polymer material that can be dissolved in an organic solvent (non-aqueous solvent) such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC) can be used. . Examples of the solvent-based solvent include N-methylpyrrolidone (NMP).

As the positive electrode current collector, a conductive member made of a metal having good conductivity is preferably used, like the current collector used in the positive electrode of a conventional lithium ion secondary battery. For example, an aluminum material or an alloy material mainly composed of an aluminum material can be used. The shape of the positive electrode current collector can be the same as the shape of the negative electrode current collector.
When manufacturing such a positive electrode, the degree of segregation of the binder in the positive electrode can be evaluated by applying the electrode evaluation method according to the present invention in the same manner as the negative electrode, and a positive electrode with better performance can be obtained. Can be produced.

  As shown in FIG. 2, when forming the wound electrode body 50, the positive electrode mixture layer non-formed portion of the positive electrode sheet 64 (that is, the portion where the positive electrode current collector 62 is exposed without forming the positive electrode mixture layer 66. ) And the negative electrode mixture layer non-formed portion of the negative electrode sheet 74 (that is, the portion where the negative electrode current collector 72 is exposed without forming the negative electrode mixture layer 80) protrudes from both sides of the separator sheet 95 in the width direction. The positive electrode sheet 64 and the negative electrode sheet 74 are superposed with a slight shift in the width direction. As a result, in the lateral direction with respect to the winding direction of the wound electrode body 50, the electrode mixture layer non-formed portions of the positive electrode sheet 64 and the negative electrode sheet 74 are respectively wound core portions (that is, the positive electrode mixture layer forming portion of the positive electrode sheet 64). And a portion where the negative electrode mixture layer forming portion of the negative electrode sheet 74 and the two separator sheets 95 are wound tightly) protrude outward. The positive electrode terminal 60 is joined to the protruding portion on the positive electrode side, and the positive electrode sheet 64 and the positive electrode terminal 60 of the wound electrode body 50 formed in the flat shape are electrically connected. Similarly, the negative electrode terminal 70 is joined to the negative electrode side protruding portion, and the negative electrode sheet 74 and the negative electrode terminal 70 are electrically connected. The positive and negative electrode terminals 60 and 70 and the positive and negative electrode current collectors 62 and 72 can be joined, for example, by ultrasonic welding, resistance welding, or the like.

As said electrolyte, the thing similar to the non-aqueous electrolyte conventionally used for a lithium ion secondary battery can be used without limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent (organic solvent). As the non-aqueous solvent, for example, one or more selected from ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like can be used. Moreover, as said support salt (support electrolyte), lithium salts, such as LiPF ₆ , can be used, for example. Further, difluorophosphate (LiPO ₂ F ₂ ) or lithium bisoxalate borate (LiBOB) may be dissolved in the non-aqueous electrolyte.
Moreover, as said separator sheet, the porous sheet (microporous resin sheet) which consists of resin can be used preferably, for example. Porous polyolefin resin sheets such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) are preferred.

  In the above-described electrode evaluation method, the interface peel strength A and the film strength B of the electrode to be evaluated were measured at a peel angle of 90 degrees, but the peel angle is as long as the interface peel strength A and the film strength B can be measured. There is no particular limitation. Hereinafter, a method for evaluating an electrode at a peel strength of 180 degrees as a second embodiment will be described with reference to FIGS. 5A to 6C.

  As shown in FIGS. 5A and 6A, the 180-degree peel strength measuring instrument 310 according to the present embodiment roughly includes a mounting table 320 on which an electrode 284 to be evaluated is mounted, and an electrode mixture of the electrode 284. And a tension jig 330 for fixing the layer 290. The tension jig 330 can adjust the tension speed, and is configured to be movable up and down in the vertical direction (the directions of the arrows X1 and X2 in FIGS. 5A and 6A) with respect to the mounting table 320. A double-sided adhesive tape 360 that can be bonded (fixed) to the surface of the electrode mixture layer 290 is attached to the lower end portion of the tension jig 330, and the electrode mixture layer 290 is an electrode on the upper portion of the tension jig 330. A measuring instrument 340 capable of measuring a peeling force when peeling from the current collector 282 is attached. By pulling up the electrode mixture layer 290 in a direction perpendicular to the mounting table 320 (the direction of the arrow X1 in FIGS. 5A and 6A), the electrode mixture layer 290 is separated from the electrode current collector 282 (so as to break. ) A double-sided adhesive tape 370 for fixing the electrode 284 is arranged on the mounting table 320 so that the electrode 284 itself does not move when peeling.

First, the measuring method of the said interface peeling strength A of the evaluation method of the electrode which concerns on 2nd Embodiment is demonstrated.
As shown in FIG. 5A, the electrode 284 to be evaluated is mounted (fixed) on the mounting table 320 via the double-sided adhesive tape 370. Note that the electrode 284 fixed to the mounting table 320 may be cut into an appropriate size as necessary.
As shown in FIG. 5A, a part of the electrode mixture layer 290 formed on the upper side of the electrode mixture layer 290 formed on both surfaces of the long electrode current collector 282 is attached to the tension jig 330. The measurement portion 292 is formed by cutting (cutting) the double-sided pressure-sensitive adhesive tape 360 so as to have a cross-sectional shape (typically circular) and a similar shape (typically the same cross-sectional area). Then, as shown in FIGS. 5A and 5B, the measurement portion 292 of the electrode mixture layer 290 is fixed to the double-sided adhesive tape 360 attached to the tension jig 330. When forming the measurement portion 292, the electrode mixture layer 290 around the measurement portion 292 does not necessarily need to be cut out as described above, and at least an incision is made in the electrode mixture layer around the measurement portion 292. Any state separated from the layer 290 may be used. Then, the measuring portion 292 of the electrode mixture layer 290 is peeled from the electrode current collector 282 at a peeling angle of 180 degrees by raising the tension jig 330 in the vertical direction (the direction of the arrow X1 in FIG. 5A) (see FIG. 5C). ). The peeling force measured by the measuring instrument 340 at this time is the interface peeling strength A at the interface between the electrode mixture layer 290 (measurement portion 292) and the electrode current collector 282, as shown in FIG. 5C. In this way, the interfacial peel strength A is measured.

Next, a method for measuring the film strength B of the electrode evaluation method according to the second embodiment will be described.
As shown in FIG. 6A, as in the case of measuring the interfacial peel strength A, the electrode 284 to be evaluated is mounted (fixed) on the mounting table 320 via the double-sided adhesive tape 370. Next, as shown in FIGS. 6A and 6B, the central portion excluding the edge portion of the electrode mixture layer 290 is fixed to the double-sided pressure-sensitive adhesive tape 360 attached to the tension jig 330. Then, by raising the tension jig 330 in the vertical direction (the direction of the arrow X1 in FIG. 6A), a part of the electrode mixture layer 290 is broken from the surrounding electrode mixture layer 290 at a peeling angle of 180 degrees. And peeled off from the electrode current collector 282 (see FIG. 6C). As shown in FIG. 6C, the peeling force measured by the measuring instrument 340 at this time is the interface peeling strength at the interface between the electrode mixture layer 290 and the electrode current collector 282 and the breaking strength of the electrode mixture layer 290 (that is, The film strength B includes the strength in the thickness direction of the electrode mixture layer 290. In this way, the film strength B is measured.
According to the electrode evaluation method of the present embodiment, it is possible to measure the interfacial peel strength A and the film strength B in a shorter time than when measuring at a peel angle of 90 degrees. The degree of segregation of the binder inside can be estimated.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[Preparation of negative electrode sheet]
<Example 1>
Weigh so that the mass ratio of natural graphite as the negative electrode active material, SBR as the binder, and CMC as the thickener is 98: 1: 1, and these materials are dispersed in water to form a paste. A composition was prepared. After applying such a composition on a negative electrode current collector (copper foil) having a thickness of 10 μm so as to be 10 mg / cm ³ (based on solid content) per side using a die coater, the composition was dried at a temperature of 60 ° C. The negative electrode sheet according to Example 1 having a negative electrode mixture layer on the negative electrode current collector was prepared by drying at a drying time of 25 seconds (conveyance speed 0.2 m / s).
<Example 2>
Weigh so that the mass ratio of natural graphite as the negative electrode active material, SBR as the binder, and CMC as the thickener is 98: 1: 1, and these materials are dispersed in water to form a paste. A composition was prepared. After applying such a composition on a negative electrode current collector (copper foil) having a thickness of 10 μm so as to be 10 mg / cm ³ (based on solid content) per side using a die coater, the composition was dried at a temperature of 160 ° C. The negative electrode sheet according to Example 2 having a negative electrode mixture layer on the negative electrode current collector was prepared by drying at a drying time of 10 seconds (conveyance speed 0.2 m / s).

[Electrode evaluation test]
For the prepared negative electrode sheets according to Example 1 and Example 2, the interfacial peel strength A and the film strength B were measured according to the electrode evaluation method of the first embodiment described above, and the strength ratio A / B was determined from these. Asked. The measurement results are shown in Table 1. Moreover, it was confirmed whether or not peeling occurred between the negative electrode mixture layer and the negative electrode current collector.
Moreover, the binder contained in the negative electrode sheets according to Examples 1 and 2 prepared above was dyed with bromine, and the degree of segregation of the binder in the negative electrode mixture layer was confirmed. That is, in the cross-sectional SEM (scanning electron microscope) image of each negative electrode mixture layer after dyeing with bromine, each negative electrode mixture layer is divided into two in the thickness direction (typically, one-dot chain lines in FIGS. 7 and 8). And the number N1 of binders in the lower layer portion adjacent to the negative electrode current collector when divided into two in the thickness direction, and farther away from the negative electrode current collector when divided in the thickness direction. The number N2 of binders in the upper layer portion was measured to determine the binder ratio (segregation index) N1 / N2. The measurement results are shown in Table 1. 7 and 8 are cross-sectional SEM images showing the state of the negative electrode mixture layer after bromine staining.

As shown in Table 1, although the negative electrode sheet according to Example 2 has a higher interfacial peel strength A than the negative electrode sheet according to Example 1, peeling occurs between the negative electrode current collector and the negative electrode mixture layer. It was confirmed. Further, from the cross-sectional SEM images of FIGS. 7 and 8, the segregation index N1 / N2 (ratio of the binder) is larger in the negative electrode sheet according to Example 1 than in the negative electrode sheet according to Example 2. In the sheet, the binder was well dispersed in the negative electrode mixture layer, but in the negative electrode sheet according to Example 2, it was confirmed that the binder was segregated on the surface side of the negative electrode mixture layer. From these results, even when the interfacial peel strength A is relatively large, if the binder is segregated in the negative electrode mixture layer, peeling occurs between the negative electrode current collector and the negative electrode mixture layer. It was confirmed.
Further, the strength ratio A / B is larger in the negative electrode sheet according to Example 1 than in the negative electrode sheet according to Example 2, and the strength ratio A / B and the segregation index N1 / N2 show the same tendency. It has been confirmed that the electrode evaluation method according to the present invention can be used as an alternative method for dyeing a binder and obtaining a segregation index from a cross-sectional SEM image.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  The electrode evaluation method according to the present invention can estimate the degree of segregation of the binder in the electrode mixture layer, and the electrode judged to be non-defective using the evaluation method is the electrode current collector and the electrode. The peel strength (adhesive strength) between the composite layers is high and the electrode is stable. For this reason, a battery (for example, a lithium ion secondary battery) including the electrode is particularly a motor (typically, an automobile equipped with an electric motor such as an automobile, particularly a hybrid automobile, an electric automobile, or a fuel automobile). It can be suitably used as a power source for an electric motor.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 15 Battery case 20 Opening part 25 Cover body 30 Case main body 40 Safety valve 50 Winding electrode body 60 Positive electrode terminal 62 Positive electrode current collector 64 Positive electrode (positive electrode sheet)
66 Positive electrode mixture layer 70 Negative electrode terminal 72 Negative electrode current collector 74 Negative electrode (negative electrode sheet)
80 Negative electrode composite material layer 82, 82A Electrode current collector 84, 84A Electrode 90, 90A Electrode composite material layer 95 Separator sheet 110 90 degree peel strength measuring instrument 120 Mounting table 130 Tensile jig (clamp)
140 Measuring instrument 150 Code 160 Double-sided adhesive tape 170 Adhesive tape 282 Electrode current collector 284 Electrode 290 Electrode composite layer 292 Measuring part 310 180 degree peel strength measuring instrument 320 Mounting table 330 Tensile jig 340 Measuring instrument 360, 370 Double-sided adhesive tape

Claims (5)

A method for evaluating segregation of the binder in the electrode mixture layer in an electrode in which an electrode mixture layer containing at least an electrode active material and a binder is formed on an electrode current collector,
Measuring the interface peel strength A at the interface between the electrode current collector and the electrode mixture layer by peeling the electrode mixture layer of the electrode to be evaluated from the electrode current collector;
A part of the electrode mixture layer of the electrode to be evaluated is peeled off from the electrode current collector so as to break from the electrode mixture layer around the electrode mixture layer. Measuring film strength B including interfacial peel strength at the interface with the material layer and breaking strength of the electrode mixture layer;
Obtaining the strength ratio A / B between the interfacial peel strength A and the film strength B, and estimating the degree of segregation of the binding material in the electrode composite material layer to be evaluated from the strength ratio A / B ,
A method for evaluating an electrode, comprising:   The method further includes determining that the product is non-defective when the intensity ratio A / B is equal to or greater than a predetermined value, and determining that the product is defective when the intensity ratio A / B is smaller than the predetermined value. The evaluation method according to claim 1, wherein the evaluation method is characterized. The interfacial peel strength A is measured by peeling the electrode mixture layer from the electrode current collector at a peel angle of 90 degrees from the edge of the electrode mixture layer, and
The film strength B is such that a part of the electrode composite layer is broken from the surrounding electrode composite layer at a peel strength of 90 degrees from the central portion excluding the edge of the electrode composite layer. The evaluation method according to claim 1, wherein the measurement is performed by peeling from the current collector. The interfacial peel strength A is obtained by cutting a part of the electrode mixture layer from the other part of the electrode mixture layer in advance and removing a part of the electrode mixture layer at the peeling angle of 180 degrees. Measured by peeling from the body, and
The film strength B is such that a part of the electrode mixture layer is broken from the surrounding electrode mixture layer at a peel strength of 180 degrees from the central portion excluding the edge of the electrode mixture layer. The evaluation method according to claim 1, wherein the measurement is performed by peeling from the current collector.   When measuring the said interface intensity | strength A and the said film | membrane intensity | strength B, the adhesive tape is previously affixed on the surface of the part which the said electrode compound-material layer peels, The any one of Claim 1 to 4 characterized by the above-mentioned. The evaluation method according to item.

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