JP6329050B2 - Method for producing electrode for lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method for producing an electrode for a lithium ion secondary battery. In this specification, the “secondary battery” refers to a battery that can be repeatedly charged. A “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of charges associated with lithium ions between the positive and negative electrodes.

  For example, in Japanese Patent Application Laid-Open No. 2014-78497, after applying a binder liquid on a current collector, a powder of granulated particles containing active material particles and a binder is deposited thereon, and the deposited layer is heated. However, it is disclosed to manufacture an electrode by applying pressure in the thickness direction.

  Japanese Patent Application Laid-Open No. 2010-277798 discloses an electrode mixture containing an active material and a binder on a current collector made of a metal foil in which a masking tape is previously attached to a region where the current collector is cut. An electrode manufacturing method is disclosed in which the masking tape is cut and peeled after applying, drying and rolling.

JP 2014-78497 A JP 2010-277798 A

By the way, the present inventors applied a binder liquid on a current collector, then supplied a powder of granulated particles containing electrode active material particles and a binder on the current collector, and formed the structure on the current collector. We are investigating the production of an electrode (positive electrode or negative electrode) in which a layer of grain particles (that is, either positive or negative electrode mixture layer) is formed. In this case, for example, the width direction of one of the positive and negative electrode composite layers formed on the current collector made of a long (band-shaped) metal foil or the like (perpendicular to the longitudinal direction of the long current collector). A phenomenon may occur in which the thickness of the electrode mixture layer is undesirably reduced at the end portion (edge portion) of the direction. Such a local thickness reduction (typically, at the edge (edge) of the electrode mixture layer) in the electrode mixture layer is caused by the peeling strength between the current collector and the electrode mixture layer. This is not preferable because it may cause a decrease or a decrease in physical strength of the electrode mixture layer itself.
The present invention has been created to solve such a problem, and suppresses a decrease in thickness at the end portion of the electrode mixture layer formed on the current collector, thereby the current collector and the electrode mixture layer. It is an object of the present invention to provide a method for producing an electrode for a lithium ion secondary battery in which the peel strength between the electrode and the electrode mixture layer itself is improved.

In order to achieve the above object, a method for producing an electrode for a lithium ion secondary battery provided by the present invention includes the following steps:
Preparing a current collector;
A step of preparing an electrode mixture made of a powder of granulated particles containing electrode active material particles and binder A;
Preparing a binder liquid B containing the binder B in a solvent;
Preparing a binder liquid C containing the binder C in a solvent;
The binder liquid B is applied in a predetermined pattern on the current collector, and the lower binder coating portion where the binder liquid B is applied on the current collector and the non-coated portion where the binder liquid B is not applied And forming;
The binder liquid C is applied to a boundary portion between the lower binder coating portion and the non-coated portion, and a binder wall portion made of the binder C is formed along the boundary between the lower binder coating portion and the non-coated portion. And a step of supplying the electrode mixture on the lower binder coat portion and forming an electrode mixture layer on the lower binder coat portion;
Is provided.

  According to the method of manufacturing a lithium ion secondary battery electrode having such a configuration, the lithium ion secondary battery electrode (positive electrode or negative electrode) in which a decrease in thickness at the end (edge) of the electrode mixture layer is suppressed may be used. .) Is obtained. Such an electrode has high peel strength between the electrode mixture layer and the current collector, and further has high strength of the electrode mixture layer itself (typically, strength at the end of the electrode mixture layer). Cheap.

In a preferred embodiment of the method for producing an electrode for a lithium ion secondary battery disclosed herein, the current collector is elongated. Then, in the process of transporting the long current collector in the longitudinal direction, a lower layer binder coating portion and a non-coating portion having a predetermined width are formed in the longitudinal direction of the current collector, and further formed in the longitudinal direction. A binder wall portion is formed in the longitudinal direction at a boundary portion between the lower binder coating portion and the non-coated portion, and then an electrode mixture layer is formed in the longitudinal direction on the lower binder coating portion.
According to the manufacturing method of this aspect, it is possible to efficiently form the lower binder coat portion, the binder wall portion, and the electrode mixture layer in the longitudinal direction of the long current collector.

In another preferable aspect of the method for producing an electrode for a lithium ion secondary battery disclosed herein, the binder liquid B and the binder liquid C include a solid content ratio NV _B of the binder liquid _B and the binder liquid C. The solid fraction NV _C is prepared so as to satisfy NV _C / NV _B > 1.
When the binder liquid C having such a relatively high solid content is used, a binder wall portion made of the binder C having a suitable height can be formed. For this reason, according to the manufacturing method of this aspect, the reduction | decrease in the thickness of the edge part (edge part) of an electrode compound-material layer is suppressed more. In addition, an electrode mixture layer having a uniform thickness can be formed throughout, and the strength of the end portion of the electrode mixture layer can be further improved.

In another preferred embodiment of the method for producing an electrode for a lithium ion secondary battery disclosed herein, the electrode mixture is formed at a height not exceeding the height of the binder wall in the electrode mixture layer forming step. It supplies on the said lower layer binder coat part.
According to this aspect, it is possible to more reliably suppress a decrease in thickness at the end portion of the electrode mixture layer formed on the current collector.

  In this specification, in order to distinguish formally the binder contained in the granulated particles (electrode mixture), the binder contained in the binder liquid B, and the binder contained in the binder liquid C, the binder A and the binder are respectively distinguished. B and Binder C are called. Here, the binder contained in the granulated particles, the binder liquid B, and the binder liquid C may all be the same material and / or composition, or only one of them may be a different material and / or composition. However, the materials and / or compositions may be different from each other.

It is a schematic diagram which shows the manufacturing apparatus 1 which embodies the manufacturing method of the electrode for lithium ion secondary batteries disclosed here. It is a schematic diagram which shows the granulated particle 8a. It is a schematic diagram of the cross section of the electrode for lithium ion secondary batteries manufactured by the manufacturing method disclosed here.

  Hereinafter, a preferred embodiment of a method for producing an electrode for a lithium ion secondary battery disclosed herein will be described. The embodiments described herein are not particularly intended to limit the present invention. Each drawing is schematically drawn. For example, the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Moreover, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description is abbreviate | omitted or simplified suitably.

"manufacturing device"
FIG. 1 is a schematic diagram showing a manufacturing apparatus 1 that embodies a method for manufacturing an electrode for a lithium ion secondary battery disclosed herein. Here, the manufacturing apparatus 1 includes a transport device 12 as shown in FIG. The conveyance device 12 is a device that conveys a long sheet-shaped current collector 20 (for example, a positive electrode current collector sheet made of a long aluminum foil) at a predetermined speed. The transport device 12 winds the unwinding unit 12A that supplies the current collector 20, a plurality of transport rolls 12B for maintaining the tension of the current collector 20, and the current collector 20 that has been subjected to predetermined processing. 12C and a drive unit 12D are provided.
In this embodiment, the long current collector 20 is subjected to a predetermined process, which will be described later, in the process of being conveyed in the longitudinal direction by the conveying device 12 to complete the lithium ion secondary battery electrode according to the present invention. Is done. According to the manufacturing method of this aspect, the electrode for lithium ion secondary batteries can be manufactured efficiently.
Specifically, the long current collector 20 is unwound from the unwinding unit 12A by the transporting roll 12B rotated by power transmission from the driving unit 12D, and is then transported to the binder liquid B supply device 13, where A binder liquid B (indicated by reference numeral 4) is applied on the current collector 20. The current collector 20 to which the binder liquid B has been applied is then conveyed to the binder liquid C supply device 14 where the binder liquid C (indicated by reference numeral 6) is applied, and then conveyed to the drying device 15. Next, the current collector 20 is conveyed to the powder supply device 16 where the powder (electrode mixture) 8 of the granulated particles 8a (see FIG. 2) is supplied. The current collector 20 supplied with the powder 8 is formed by passing through the squeegee member 17, and further pressed by passing between the pair of rolling rolls 18 and 19, and finally wound at the winding portion 12C. Taken.

<< Method for producing electrode for lithium ion secondary battery >>
The method for manufacturing an electrode for a lithium ion secondary battery according to the present embodiment roughly includes the following steps 1 to 7.
1. Step of preparing a current collector 2. Step of preparing an electrode mixture made of granulated powder containing electrode active material particles and binder A 3. preparing a binder liquid B containing the binder B in a solvent; 4. preparing a binder liquid C containing the binder C in a solvent; The binder liquid B is applied in a predetermined pattern on the current collector, and the lower binder coating portion where the binder liquid B is applied on the current collector and the non-coated portion where the binder liquid B is not applied 5. forming The binder liquid C is applied to the boundary portion between the lower binder coating portion and the non-coated portion, and a binder wall portion made of the binder C is formed along the boundary between the lower binder coating portion and the non-coated portion. Step 7 Step of supplying the electrode mixture on the lower binder coat portion and forming an electrode mixture layer on the lower binder coat portion Hereinafter, each step will be described more specifically.

<< Process for preparing current collector >>
In step 1, a current collector 20 is prepared. The current collector 20 prepared here is a member from which electricity is extracted at the electrode. For example, the current collector 20 used in the lithium ion secondary battery is made of a material that is excellent in electronic conductivity and stably exists inside the battery. In addition, weight reduction, required mechanical strength and ease of processing are required. For example, an aluminum foil is preferably used as the current collector 20 for the positive electrode of a lithium ion secondary battery. Further, a copper foil is preferably used as the current collector 20 for the negative electrode. As shown in FIG. 1, the current collector 20 may be a long (band-shaped) material. For example, the current collector 20 is a strip-shaped metal foil (specifically, an aluminum foil having a thickness of 10 to 20 μm (typically 15 ± 1 μm), or a thickness of 5 to 20 μm (typically 10 ± 2 μm). ) Copper foil) is preferably used. Such a long current collector 20 is prepared in a state of being wound around a winding core.
The current collector 20 is not limited to a metal foil. For example, depending on the application of the manufactured electrode, the current collector 20 may be a resin film having conductivity. Here, “preparing” may be, for example, obtaining a desired current collector 20 from a material manufacturer as appropriate.

<Process for preparing granulated powder>
In step 2, a granulated particle 8a powder (electrode mixture) 8 is prepared. FIG. 2 is a schematic diagram showing the granulated particles 8a. The granulated particles 8a prepared here preferably include at least electrode active material particles 9 and a binder A (indicated by reference numeral 10). The powder 8 of the granulated particles 8a can be obtained, for example, by granulating a mixture (suspension) obtained by mixing the electrode active material particles 9 and the binder A10 with a solvent by a spray drying method. In the spray dry manufacturing method, the mixture is sprayed in a dry atmosphere. At this time, the particles contained in the sprayed droplets are roughly granulated as one lump. For this reason, the solid content amount (solid content ratio) contained in the granulated particles 8a and the size and mass of the granulated particles 8a can be adjusted by adjusting the size of the droplets. The sprayed droplets preferably include at least the electrode active material particles 9 and the binder A10. The droplets to be sprayed may contain materials other than the electrode active material particles 9 and the binder A10, and may contain, for example, a conductive material. The granulated particles 8a prepared here may have, for example, an average particle size of about 60 μm to 100 μm.
In the present specification, unless otherwise specified, the “average particle size” means a particle size at an integrated value of 50% in a particle size distribution measured based on a particle size distribution measuring apparatus based on a laser scattering / diffraction method, that is, 50%. It shall mean the volume average particle diameter.

<Electrode active material particles>
The manufacturing method of the electrode for lithium ion secondary batteries disclosed here is applicable to any of various electrodes, that is, a positive electrode and a negative electrode. The electrode active material particles 9 contained in the granulated particles 8a differ depending on the electrodes to be produced. For example, when manufacturing a positive electrode of a lithium ion secondary battery, active material particles used for the positive electrode are used as the electrode active material particles 9. Moreover, when manufacturing the negative electrode of a lithium ion secondary battery, the active material particle used for this negative electrode as the electrode active material particle 9 is used.

<Examples of active material particles used for the positive electrode of a lithium ion secondary battery>
As a suitable example of the electrode active material particle 9 used for the positive electrode of a lithium ion secondary battery, lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), lithium manganese oxide (for example, LiMn ₂ O _4). ), An oxide (lithium transition metal oxide) containing lithium and a transition metal element as constituent metal elements such as lithium nickel cobalt manganese oxide (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), Examples thereof include phosphates containing lithium and a transition metal element as constituent metal elements such as lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ). These are used in the form of particles and are appropriately referred to as positive electrode active material particles. One or two or more positive electrode active material particles may be used. Since these positive electrode active material particles have low conductivity, the positive electrode mixture layer containing the positive electrode active material particles preferably contains a conductive material in order to increase conductivity. In this case, the conductive material may be included in droplets sprayed by spray drying.

<Examples of active material particles used for the negative electrode of a lithium ion secondary battery>
Preferable examples of the active material particles used for the negative electrode of the lithium ion secondary battery include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal oxides, and lithium transition metal nitrides. These are used in the form of particles and are appropriately referred to as negative electrode active material particles. One kind or two or more kinds of negative electrode active material particles may be used. The negative electrode mixture layer containing the negative electrode active material particles may contain a conductive material in order to increase conductivity. In this case, the conductive material is included in the droplets sprayed by spray drying. Good.

<Conductive material (conductive auxiliary agent)>
Examples of the conductive material include carbon materials such as carbon powder and carbon fiber. One kind selected from such conductive materials may be used alone, or two or more kinds may be used in combination. As the carbon powder, various carbon blacks (for example, acetylene black, oil furnace black, graphitized carbon black, carbon black, ketjen black), graphite powder, and the like can be used. Such a conductive material is suitably added, for example, when the electrode active material particles 9 having poor conductivity are used for the purpose of forming a conductive path between the electrode active material particles 9 and the current collector 20.

<Binder A>
Next, the binder A10 included in the granulated particles 8a in the step of preparing the granulated particles 8a will be described. Here, the granulated particles 8a are preferably granulated by a spray drying method. Therefore, a polymer that can be dissolved or dispersed in a solvent is used for the binder A10 included in the granulated particles 8a. Examples of the polymer that can be dissolved or dispersed in the aqueous solvent include rubbers (styrene butadiene copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), etc.), vinyl acetate copolymer, acrylate polymer, and the like. Can be mentioned. Examples of the polymer that can be dissolved or dispersed in the non-aqueous solvent include polyvinylidene fluoride (PVDF). Further, as the binder A10 included in the granulated particles 8a, a cellulose polymer, a fluorine resin (for example, polytetrafluoroethylene (PTFE)) or the like may be used. In addition, although binder A10 included in the granulated particle 8a is illustrated here, the binder A10 included in the granulated particle 8a is not limited to that illustrated here.

<< Process for Preparing Binder Liquid B >>
In step 3, a binder liquid B4 is prepared. The binder liquid B4 prepared here is a mixed liquid (composition) in which the binder B is mixed with a solvent. As the solvent for the binder liquid B4, a so-called aqueous solvent is preferably used from the viewpoint of reducing the environmental load. In this case, water or a mixed solvent mainly composed of water is used. The solvent of the binder liquid B4 is not limited to a so-called aqueous solvent, and may be a so-called organic solvent system. Examples of the organic solvent type include N-methylpyrrolidone (NMP).

  Moreover, as the binder B contained in binder liquid B4, what can be disperse | distributed to a solvent is preferable. When an aqueous solvent is used as the solvent, as the binder B, for example, styrene butadiene rubber (SBR), polyacrylic acid (PAA), or the like can be preferably used. When an organic solvent-based solvent is used, for example, polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), or the like can be preferably used as the binder B. As a suitable example of binder liquid B4, what uses an acrylic resin (for example, polymethacrylic ester resin) as binder B in the positive electrode of a lithium ion secondary battery, for example is mentioned as binder B, for example. Moreover, as a negative electrode of a lithium ion secondary battery, what uses water as a solvent and uses SBR as binder B is mentioned.

The solid fraction (hereinafter also referred to as “NV _B ”) of the binder liquid B4 is not particularly limited, but the solid fraction NV _B is from the viewpoint of improving the peel strength between the current collector 20 and the electrode mixture layer. The amount is usually 5% by weight or more, preferably 10% by weight or more, more preferably 15% by weight or more, and further preferably 20% by weight or more. The solid content NV _B is usually 50% by weight or less, preferably 40% by weight or less, more preferably 35% by weight or less, from the viewpoint of the coating property of the binder liquid B4. is there.

<< Process for Preparing Binder Liquid C >>
In step 4, a binder liquid C6 is prepared. The binder liquid C6 prepared here is a mixed liquid (composition) in which the binder C is mixed with a solvent. As the solvent of the binder liquid C6, an aqueous solvent (water or a mixed solvent mainly composed of water) is preferably used for the same reason as the binder liquid B4 described above. Further, the solvent of the binder liquid C6 is not limited to a so-called aqueous solvent, and may be a so-called organic solvent system. Examples of the organic solvent type include N-methylpyrrolidone (NMP).

  Moreover, as the binder C contained in the binder liquid C6, what can be disperse | distributed to a solvent is preferable. When an aqueous solvent is used as the solvent, as the binder C, for example, styrene butadiene rubber (SBR), polyacrylic acid (PAA), or the like can be preferably used. When an organic solvent-based solvent is used as the solvent, for example, polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), or the like can be preferably used as the binder C. As a suitable example of the binder liquid C6, for example, in a positive electrode of a lithium ion secondary battery, water mixed with an acrylic resin (for example, polymethacrylic ester resin) as a binder is used. Moreover, the negative electrode of a lithium ion secondary battery includes a mixture of water as a solvent and SBR as a binder.

  The types of the solvent contained in the binder liquid B4 and the solvent contained in the binder liquid C6 may be the same or different from each other. Further, the binder B and the binder C may be the same material or different from each other. From the viewpoint of reducing the types of impurities that can be mixed, or from the viewpoint of simplifying the process of preparing the binder liquid B and the binder liquid C, the types of solvents contained in the binder liquids B and C are preferably the same. For the same reason, it is preferable that the binder B and the binder C are the same material.

It is appropriate that the solid content ratio NV _C of the binder liquid C6 is usually 10% by weight or more. The solid content NV _C is preferably 20% by weight or more, more preferably 30% by weight or more, and still more preferably 40% by weight or more. When the solid content ratio NV _C is equal to or higher than the lower limit value described above, the height of the binder wall portion made of the binder C tends to increase. A binder wall portion having a large height is preferable because it can suitably serve as a wall that suppresses the electrode mixture layer from sagging at the end thereof. Further, suppressing When more than the lower limit value above the solid fraction NV _C, handling of the electrode (e.g., the winding operation of the electrode) at the time of the, that undesirably electrode sticks to the other part And workability tends to be improved. The upper limit value of the solid content ratio NV _C is not particularly limited. The solid content NV _C is usually 60% by weight or less, preferably 50% by weight or less, more preferably 45% by weight or less, from the viewpoint of the coating property of the binder liquid C.

The solid fraction NV _C of the binder liquid C6 is preferably equal to or higher than the solid fraction NV _B of the binder liquid B4. In other words, the ratio of the NV _C for _{NV B (NV C / NV B} ) is preferably greater than 1. The (NV _C / NV _B ) is more preferably 1.2 or more, and further preferably 1.5 or more. When the above (NV _C / NV _B ) is not less than the lower limit value described above, a binder wall portion having a suitable height can be formed, and sagging at the end portion of the electrode mixture layer can be suitably suppressed. Although the upper limit of the (NV _C / NV _B ) is not particularly limited, from the viewpoint of the coating property of the binder liquid C, the (NV _C / NV _B ) is usually 5 or less, preferably 2 or less. is there.

<< Process for forming lower binder coat part and non-coating part >>
In step 5, the binder liquid B4 is applied on the current collector 20. The binder liquid B4 may be applied to the current collector 20 in a predetermined pattern, for example. Further, the binder liquid B4 is preferably applied as thin as about 1 to 20 μm, for example, and may be applied by gravure printing or the like. For example, a direct gravure roll coater can be used for the binder liquid B supply device 13 shown in FIG. In the binder liquid B supply device 13, the binder liquid B <b> 4 is transferred to the current collector 20 by direct gravure using a gravure roll engraved with a fine pattern on the surface. The gravure roll may have, for example, a plurality of grooves having a plate depth of about 10 μm to 30 μm (for example, 20 μm), a width along a slanting line inclined with respect to the rotation axis, 50 μm, and a pitch of 200 μm. . Further, the pattern of grooves formed on the gravure roll may be a horizontal stripe pattern or a lattice pattern. The lattice shape may be, for example, a pattern in which oblique lines are combined in a lattice shape. Moreover, the horizontal stripe shape is good to apply | coat binder liquid B4 with the space | interval predetermined along the width direction of the elongate collector 20 and the longitudinal direction. The groove width and pitch of the gravure roll may be variously changed.

  Although not shown in FIG. 1, in the transport device 12, the long current collector 20 is transported with the processing surface (surface on which the electrode mixture layer is formed) coated with the binder liquid B4 facing downward. A gravure roll may be applied to the current collector 20. In this case, the binder liquid B4 may be applied to the current collector 20 with a thickness of about 1 μm to 10 μm, for example.

<Process for forming binder wall>
Step 6 typically includes a step of applying the binder liquid C6 onto the current collector 20, and a step of drying the applied binder liquid C6. In the step of applying the binder liquid C6, the binder liquid C6 includes an area where the binder liquid B4 is applied on the current collector 20 (lower binder coating part) and an area where the binder liquid B4 is not applied (non-coated part). It is applied to the boundary. When the current collector 20 has a long shape, the region to which the binder liquid C6 is applied is the boundary along the longitudinal direction of the long current collector 20. When the binder liquid C6 is applied to the long current collector 20 as described above, the binder liquid C6 is applied with a predetermined width along the boundary.

Here, that the binder liquid C6 is applied to the boundary portion between the lower binder coating portion and the non-coated portion means that part or all of the region (binder wall portion) to which the binder liquid C6 is applied is the lower binder coating. It does not exclude overlapping with the part. Moreover, it does not exclude that a part or all of the region (binder wall portion) to which the binder liquid C6 is applied overlaps with the non-coated portion. Furthermore, it does not exclude the presence of an uncoated portion between the lower layer binder coat portion and the binder wall portion.
That is, in one aspect of the electrode manufacturing method disclosed herein, the lower layer binder coat part and at least a part of the binder wall part may be laminated. In another aspect of the electrode manufacturing method disclosed herein, at least some of the binder wall portions may not be in contact with the lower layer binder coat portion. For example, when there is a non-coated part between the lower binder coating part and the binder wall part, the size in the width direction of the non-coated part improves the peel strength between the electrode mixture layer and the current collector. From this point of view, it is preferably 0.5% or less of the total width of the current collector 20, and more preferably 0.3% or less (for example, 0.1% or less).

  The size in the width direction where the binder liquid C6 is applied is not particularly limited as long as it is appropriately adjusted according to the desired width of the binder wall. For example, the size in the width direction of the binder liquid C6 applied to the long current collector 20 is usually 5% or less of the total width of the current collector 20, preferably 3% or less, more preferably 1%. It is as follows. If the width to which the binder liquid C6 is applied is equal to or less than the above-described upper limit, it is easy to secure a space for forming the electrode mixture layer, and thus the battery capacity can be improved.

  By drying the binder liquid C6 applied to the current collector 20, a binder wall portion made of the binder C is formed. The drying method of the binder liquid C6 applied to the current collector 20 is not particularly limited, and various known methods can be used. In the example shown in FIG. 1, the current collector 20 to which the binder liquid C6 has been applied is conveyed to the drying device 15. In the drying device 15, wind (typically hot air) is discharged toward the area where the binder liquid C6 is applied. Here, discharging the wind toward the area where the binder liquid C6 is applied refers to sending the wind (airflow) with the application part of the binder liquid C6 in the current collector 20 as a main target. This means that it is possible to hit other parts than the application part. The time for applying air (drying time), the air volume, and the temperature of the air are not particularly limited, and may be set so that the binder liquid C6 applied on the current collector 20 is appropriately dried.

<< Step of forming electrode mixture layer >>
In step 7, the powder 8 of the granulated particles 8a is supplied onto the current collector 20, and an electrode mixture layer is formed.

<Powder supply device>
The powder supply device 16 is a device for supplying the powder (electrode mixture) 8 of the granulated particles 8 a onto the current collector 20. Here, the supply amount of the powder (electrode mixture) 8 is preferably set in relation to the height of the binder wall portion formed in step 6. From the viewpoint of suitably suppressing the decrease in the thickness of the end portion of the electrode mixture layer, the powder (electrode mixture) 8 is preferably supplied at a height that does not exceed the height of the binder wall portion.

  A suitable supply amount of the powder (electrode mixture) 8 will be described with reference to FIG. FIG. 3 is a diagram schematically illustrating an electrode manufactured by the manufacturing method disclosed herein. More specifically, FIG. 3 shows a state after the powder (electrode mixture) 8 is supplied onto the current collector 20 in Step 7. As shown in this figure, on the surface of the current collector 20, the lower layer binder coating portion formed by applying the binder liquid B4 in a predetermined pattern and the non-coating where the binder liquid B4 is not applied The binder wall C22 is formed by applying the binder liquid C6 to the boundary region between the two parts and drying it. And after forming this binder wall part 22, the powder (electrode mixture) 8 is supplied on the lower layer binder coat part, and the electrode mixture layer 24 is formed.

  Here, as shown in FIG. 3, when the powder (electrode mixture) 8 is supplied so that the height of the electrode mixture layer 24 is equal to or less than the height of the binder wall portion 22, The wall portion 22 can preferably serve as a wall for blocking a part of the electrode mixture 8 supplied on the current collector 20 from flowing out from the lower binder coating portion to the non-coating portion side. For this reason, according to the electrode of this aspect, the thickness reduction in the edge part of the electrode compound-material layer 24 can be suppressed more reliably. Here, the height of the binder wall portion 22 in FIG. 3 refers to the distance from the lower surface of the current collector 20 to the upper surface of the binder wall portion 22. Further, the height of the electrode mixture layer 24 in FIG. 3 is a region where the upper surface of the electrode mixture layer 24 is flat from the lower surface of the current collector 20 (that is, the end portion of the electrode mixture layer 24). This is the distance to the upper surface in the region excluding the region where the thickness is reduced.

<Squeegee member>
According to one aspect of the electrode manufacturing method disclosed herein, after supplying the powder 8 of the granulated particles 8 a onto the current collector 20, the powder 8 is formed by the squeegee member 17. In the example shown in FIG. 1, a squeegee member 17 is provided on the downstream side of the powder supply device 16 (downstream side in the conveyance path of the current collector 20). The squeegee member 17 adjusts the thickness of the powder 8 supplied on the current collector 20. For example, there is a gap between the squeegee member 17 and the current collector 20 being conveyed, and the thickness of the powder 8 passing through the gap is adjusted according to the gap. In the embodiment shown in FIG. 1, the squeegee member 17 is a cylindrical roller member. The squeegee member 17 may be a blade-shaped member. Excess powder 8 that cannot pass through the squeegee member 17 is removed from above the current collector 20.

  The size of the gap between the squeegee member 17 and the current collector 20 is set in consideration so that the height of the powder (electrode mixture) 8 does not exceed the height of the binder wall. It is preferable. For example, the gap can be adjusted to about 100 μm to 300 μm (preferably about 150 μm to 250 μm).

<Rolling roller>
According to one aspect of the electrode manufacturing method disclosed herein, the powder 8 of the granulated particles 8 a formed by the squeegee member 17 is then pressed against the current collector 20. In the example shown in FIG. 1, the current collector 20 formed with the powder 8 passes through rolling rollers 18 and 19. The rolling rollers 18 and 19 are members that sandwich the powder 8 of the granulated particles 8 a and the current collector 20. In this embodiment, the rolling rollers 18 and 19 each have a rotating shaft arranged horizontally, and the outer peripheral surfaces are opposed in the horizontal direction. The current collector 20 is conveyed along the rolling roller 19 on one side. A current collector 20 in which the powder 8 is formed by the squeegee member 17 is supplied to the rolling rollers 18 and 19.

  The distance between the rolling rollers 18 and 19 may be adjusted in consideration of the thickness of the powder 8 deposited on the current collector 20. By passing the rolling rollers 18 and 19, the powder 8 of the granulated particles 8 a is pressed against the current collector 20 with an appropriate strength. As a result, the number of contact points of the binder A10 increases in the powder 8 of the granulated particles 8a, and a required adhesion force is obtained on the granulated particles 8a. Thereby, the layer (electrode mixture layer) 24 of the powder (electrode mixture) 8 of the granulated particles 8 a including the electrode active material particles 9 (see FIG. 2) on the current collector 20 has a substantially constant thickness. Is formed.

  Here, when forming the electrode mixture layer 24 on both surfaces of the current collector 20, after forming the electrode mixture layer 24 on one surface of the current collector 20 by the above method, The electrode mixture layer 24 may be formed on the opposite surface of the current collector 20.

  The electrode manufactured by the manufacturing method disclosed herein has good productivity and stable quality electrodes. For this reason, it is preferably used in applications that require mass productivity and stable performance. As such an application, for example, a power source (drive power source) for a motor mounted on a vehicle can be cited. The type of vehicle is not particularly limited, and examples thereof include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, motorbikes, electric assist bicycles, electric wheelchairs, electric railways, and the like. It is done. Such a lithium ion secondary battery may be used in the form of an assembled battery formed by connecting a plurality of them in series and / or in parallel.

  Examples of the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples. In the following examples, a method for producing a positive electrode of a lithium ion secondary battery will be described. By appropriately changing a current collector, an active material, a conductive material, and the like, the present invention can be applied to a negative electrode of a lithium ion secondary battery. This method can also be applied.

Example 1
As the positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having an average particle diameter of 4.5 μm was used. Acetylene black (AB) was used as the conductive material. As the binder A, an acrylic resin binder having a number average molecular weight Mn of 35 × 10 ⁴ was used. Then, a conductive material and binder A are first added and mixed in a dry particle composite device (Hosokawa Micron Co., Ltd., Nobilta 130), then a positive electrode active material and a small amount of water are added, and a dispersion power of 3 kW is added. Then, the mixture was mixed for about 10 hours, and the resulting mixture was appropriately pulverized and classified to obtain granulated particles having an average particle size of 40 μm or more.

In order to prepare the binder liquids B and C, water was used as a solvent, and acrylic resin binders were used as the binders B and C. At this time, the solid fraction NV _B of the binder liquid B was 30% by weight. On the other hand, a solid fraction NV _C binder solution C was 45 wt%.

  As the positive electrode current collector, a long aluminum foil having a thickness of about 15 μm and a width of 260 mm was used. The binder liquid B prepared above was subjected to pattern coating at a predetermined position of the positive electrode current collector using a direct gravure roll coater. At this time, in one end portion (edge portion) in the width direction of the long current collector, a region that is not coated with a pattern (non-coated portion) along the longitudinal direction of the current collector Was provided. Thereafter, the binder liquid C was applied in the form of a strip having a width of 2 mm in the vicinity of the boundary between the pattern-coated region and the non-coated region. Next, the binder liquid C was sufficiently dried by applying air to the portion of the current collector on which the binder liquid C was applied to form a binder wall. At this time, the height of the binder wall (the distance from the lower surface of the current collector to the upper surface of the binder wall) was about 70 μm.

The prepared granulated particles were accommodated in a powder feeder and supplied at a predetermined supply rate toward the area where the binder liquid B on the current collector was coated. An excessive amount of the granulated particles supplied onto the current collector was scraped by a squeegee with a height sensor provided downstream. The current collector is applied with pressure from above and below by a rolling roll installed further downstream, so that a positive electrode active material layer having a thickness of about 48 μm and a basis weight (per side) of about 13 mg / cm ² is formed on the current collector. (Positive electrode mixture layer) was formed. The positive electrode sheet produced by the above procedure was used as the positive electrode according to Example 1.

(Comparative Example 1)
A positive electrode according to Comparative Example 1 was produced in the same manner as the positive electrode production method according to Example 1 described above, except that the binder liquid C was not applied onto the current collector.

(Cutting strength)
About the positive electrode which concerns on each example, the intensity | strength of the positive mix layer (positive electrode active material layer) was measured. Here, the strength of the positive electrode mixture layer refers to a so-called cutting strength. Specifically, the cutting force is inserted into the positive electrode mixture layer according to each example to a depth of 10 μm, and the reaction force received by the blade when the blade is moved horizontally along the longitudinal direction of the current collector is measured. did. A value (unit: N / mm) obtained by dividing the obtained reaction force by the width of the cutting blade (here, 500 μm (0.5 mm)) was defined as the cutting strength. The cutting strength of the positive electrode mixture layer was measured at two locations, the central portion in the width direction and the end portion in the width direction of the positive electrode. Specifically, the central portion is a portion that is substantially the center in the width direction of the positive electrode mixture layer. Further, the end portion refers to a boundary between the positive electrode mixture layer and the binder wall portion (if the positive electrode does not include the binder wall portion, a boundary between the positive electrode mixture layer and the non-coated portion). It is the place which entered 0.25 mm inside toward the center part of the width direction. The cutting strength was measured 6 times for each measurement position, and the average value was calculated. The results are shown in Table 1. Table 1 also shows the relative value of the cutting strength at the end when the cutting strength at the center of each example is 100%.

  As is clear from Table 1, it was found that the strength of the end portion of the positive electrode mixture layer according to Example 1 was greatly improved as compared with the strength of the end portion of the positive electrode mixture layer according to Comparative Example 1. Further, the strength of the end portion of the positive electrode mixture layer according to Comparative Example 1 is about 27% lower than the strength of the center portion thereof, whereas the strength of the end portion of the positive electrode mixture layer according to Example 1 is lower than the center portion thereof. It was found that the rate of decrease in strength was about 12%. The above result is considered to be due to the reduction in the thickness of the end portion of the positive electrode mixture layer being suppressed by the formation of the binder wall portion in the electrode (positive electrode) according to Example 1.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

1 Manufacturing equipment 4 Binder liquid B
6 Binder liquid C
8 Powder (electrode mixture)
8a Granulated particles 9 Electrode active material particles 10 Binder A
DESCRIPTION OF SYMBOLS 12 Conveyance apparatus 13 Binder liquid B supply apparatus 14 Binder liquid C supply apparatus 15 Drying apparatus 16 Powder supply apparatus 17 Squeegee members 18 and 19 Rolling roll 20 Current collector 22 Binder wall part 24 Electrode mixture layer

Claims (4)

A method for producing an electrode for a lithium ion secondary battery, comprising the following steps:
Preparing a current collector;
A step of preparing an electrode mixture made of a powder of granulated particles containing electrode active material particles and binder A;
Preparing a binder liquid B composed of the binder B and water ;
Preparing a binder liquid C composed of a binder C and water , wherein the binder B and the binder C are the same binder material ;
The binder liquid B is applied in a predetermined pattern on the current collector, and the lower binder coating portion where the binder liquid B is applied on the current collector and the non-coated portion where the binder liquid B is not applied And forming;
By applying the binder liquid C to the boundary part between the lower layer binder coat part and the non-coated part , and drying the applied binder liquid C, at the boundary between the lower layer binder coat part and the non-coated part. Forming a binder wall portion made of the binder C along the step; and supplying the electrode mixture on the lower binder coat portion and forming an electrode mixture layer on the lower binder coat portion;
A method for producing an electrode for a lithium ion secondary battery. The current collector is elongated,
In the process of transporting the long current collector in the longitudinal direction, the lower binder coating portion and the non-coated portion of a predetermined width are formed in the longitudinal direction of the current collector,
Furthermore, the binder wall portion is formed in the longitudinal direction at the boundary portion between the lower layer binder coat portion and the non-coated portion formed in the longitudinal direction,
Subsequently, the manufacturing method of the electrode for lithium ion secondary batteries described in Claim 1 which forms the said electrode compound-material layer in a longitudinal direction on the said lower layer binder coat part. The binder liquid B and the binder liquid C are prepared so that the solid content ratio NV _B of the binder liquid _B and the solid content ratio NV _C of the binder liquid C satisfy NV _C / NV _B > 1. The manufacturing method of the electrode for lithium ion secondary batteries of Claim 1 or 2. The said electrode compound material layer formation process WHEREIN: The said electrode compound material is supplied on the said lower layer binder coat part by the height which does not exceed the height of the said binder wall part. A method for producing an electrode for a lithium ion secondary battery.

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