JP5640996B2 - Battery electrode manufacturing method and battery electrode - Google Patents

Description

  The present invention relates to a method for manufacturing a battery electrode and a battery electrode. More specifically, the present invention relates to a battery electrode manufacturing method for forming an electrode by powder molding and a battery electrode.

  Conventionally, in order to produce an electrode for a non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery), a powdered electrode material granulated on a current collector foil is supplied, and an electrode mixture is prepared by a roll press. A method of forming a layer is known (see, for example, Patent Document 1).

  Patent Document 1 describes a pressure molding method in which composite particles (granulated particles) are powder-molded into a sheet as a method for producing an electrode used in a lithium ion secondary battery or the like. The pressure forming method is a method of forming an electrode layer (electrode mixture layer) by applying pressure to the composite particles to perform densification by rearrangement and deformation of the electrode layer forming material. As an example of pressure molding by the pressure molding method, for example, there is a roll pressure molding method in which composite particles are supplied to a roll-type pressure molding device by a supply device such as a screw feeder to mold an electrode layer.

JP 2009-212113 A

  However, as described in Patent Document 1, when the electrode mixture layer is formed on the current collector foil by powder forming by so-called roll press, it is high at the time of pressing in order to ensure the peel strength of the electrode mixture layer. Although pressure is required, the density of the electrode mixture layer (electrode density) increases as a contradiction. When the density of the electrode mixture layer is too high, the electrolyte performance and the solution resistance are increased, so that the battery performance is deteriorated. That is, when the electrode mixture layer is formed so as to have a desired density with emphasis on battery performance, there is a problem that the peel strength of the electrode mixture layer is lowered. For this reason, there is a demand for a battery electrode that prevents excessive densification of the electrode mixture layer and improves the peel strength of the electrode mixture layer even when high-pressure pressing is performed.

  When a negative electrode (negative electrode sheet) used in a lithium ion secondary battery is manufactured, when graphite is used as the negative electrode active material, an electrode structure in which the graphite is ideally magnetically oriented as shown in FIG. It is known that the battery performance is improved by doing so.

  However, when a negative electrode (negative electrode sheet) is produced by powder molding (dry process) using granulated particles (graphite) as in Patent Document 1, a plurality of graphite particles are randomly oriented as shown in FIG. Since the electrode structure is composed of a group of granulated particles, the orientation of graphite is difficult to occur. That is, because the graphite is fixed in a state of being randomly oriented as granulated particles (secondary particles) together with other electrode mixture components in the granulation step, a magnetic field is then applied to the graphite in the granulated particles. Even if is applied, orientation does not occur. That is, when graphite is used as primary particles constituting the granulated particles, it is difficult to improve battery performance by orienting the graphite of the primary particles in a magnetic field.

  Then, this invention is made | formed in view of the said subject, and it aims at providing the manufacturing method and battery electrode of a battery electrode which the peeling strength of the electrode mixture layer and the battery performance improved.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
In the method for producing an electrode for a battery for forming an electrode by supplying an electrode mixture powder obtained by granulating an electrode mixture onto a current collector foil and pressing it,
Including graphite in the electrode mixture;
It is a manufacturing method of the battery electrode which obtains the electrode mixture powder by drying and granulating the electrode mixture containing the graphite while applying a magnetic field.

In claim 2,
After supplying the electrode mixture powder onto the current collector foil, the electrode mixture powder is applied to the current collector foil by further applying a magnetic field to the current collector foil before performing the pressing. This is a battery electrode manufacturing method in which the orientation is controlled substantially vertically.

In claim 3,
It is a battery electrode manufactured by the manufacturing method of the battery electrode of Claim 1 or Claim 2.

  The present invention has the following effects.

  In claim 1, by granulating while applying a magnetic field, the orientation of graphite in the particles constituting the electrode mixture powder is aligned (the voids in the particles constituting the electrode mixture powder are reduced), Pressure is preferentially applied to the graphite oriented at the time of pressing, and the electrode mixture is not easily crushed, and the electrode mixture layer can be kept at a low density. That is, a desired electrode density can be maintained even when high-pressure pressing is performed, and the peel strength is also improved.

  In Claim 2, since graphite can be oriented substantially perpendicular to the current collector foil, the electrode mixture layer can be kept at a lower density, and the peel strength is further improved.

  In claim 3, by granulating while applying a magnetic field, the orientation of the graphite in the particles constituting the electrode mixture powder is aligned (the voids in the particles constituting the electrode mixture powder are reduced), Pressure is preferentially applied to the graphite oriented at the time of pressing, and the electrode mixture is not easily crushed, and the electrode mixture layer can be kept at a low density. That is, a desired electrode density can be maintained even when high-pressure pressing is performed, and the peel strength is also improved.

The schematic diagram which shows the structure of the manufacturing apparatus of the electrode for batteries which concerns on one Embodiment of this invention. The figure which shows the flow of the manufacturing method of the battery electrode which concerns on one Embodiment of this invention. The image figure of the granulated particle orientated by the magnetic field. The schematic diagram which shows the electrode structure which concerns on one Embodiment of this invention. The image figure which shows the state which the granulated particle which concerns on a present Example orientated. (A) is an image figure which shows the electrode structure of the negative electrode produced with the conventional powder molding method, (b) is an image figure which shows the electrode structure of the negative electrode which concerns on Example 1. FIG. The figure which shows the relationship between a graphite orientation degree (magnetic field orientation degree) and IV resistance (initial resistance). The figure which shows the relationship between graphite orientation degree ((110) / (002) strength ratio) and graphite particle shape. The figure which shows the peeling strength of each negative electrode of an Example and a comparative example. The schematic diagram which shows an ideal electrode structure. The schematic diagram which shows the structure of the electrode produced with the conventional powder molding method.

Next, embodiments of the invention will be described.
First, a battery electrode manufacturing apparatus 1 according to this embodiment will be described with reference to FIG.

[Battery electrode manufacturing equipment]
Battery electrode manufacturing apparatus 1 (hereinafter referred to as electrode manufacturing apparatus 1) collects a powdered electrode mixture (hereinafter referred to as electrode mixture powder 7) obtained by granulating an electrode mixture. It is an apparatus for forming a sheet-like electrode by pressing (compression molding) the current collector foil 6 supplied on the foil 6 and supplied with the electrode mixture powder 7. As shown in FIG. 1, the electrode manufacturing apparatus 1 includes a powder forming apparatus 2, a conveying means 3, a flattening means (flattening blade 4), a magnetic field applying means 5, a heating means (infrared heating means 9), and a hot press means. 10 is mainly composed. For example, in manufacturing a lithium ion secondary battery, the electrode manufacturing apparatus 1 supplies the electrode mixture powder 7 to the surface of a current collector foil (metal foil such as copper) that is an electrode base material, and the electrode mixture is applied to the surface. It is applicable when manufacturing an electrode (electrode sheet) on which the layer 8 is formed.

  The powder molding apparatus 2 is an apparatus that supplies the electrode mixture powder 7 onto the current collector foil 6 and forms the electrode mixture powder 7 on the current collector foil 6 as a deposited layer. The powder molding apparatus 2 includes a supply device (not shown) for supplying the electrode mixture powder 7, and the electrode mixture powder 7 can be deposited on the current collector foil 6 by the supply device.

  The conveying means 3 is means for conveying the current collector foil 6 in order to the powder forming apparatus 2, the flattening blade 4, the magnetic field applying means 5, the heating means 9, and the hot press means 10, and a plurality of conveying means. And driving means for driving the conveying roller. The conveying means 3 can convey the electrode mixture powder 7 supplied from the powder forming apparatus 2 onto the current collector foil 6 to the downstream side by driving the driving means.

  The flattening blade 4 is a blade member that is provided on the downstream side of the powder molding apparatus 2 and that has a sharp tip at the tip. The tip is directed downward and between the tip and the surface of the current collector foil 6. The arrangement is fixed at a predetermined interval. The flattening blade 4 flattens the electrode mixture powder 7 supplied onto the current collector foil 6 by the powder molding apparatus 2 and deposits the electrode mixture powder 7 having the same thickness as the predetermined interval. It is a planarization means for forming.

  The magnetic field applying means 5 is provided on the downstream side of the powder molding apparatus 2 and is arranged so as to pass the current collector foil 6 through the center of the magnetic field applying means 5 and is flattened by the flattening blade 4. A magnetic field (magnetic force) along the thickness direction (perpendicular to the current collector foil 6; vertical direction in FIG. 1) can be applied to the deposited layer of the powder 7 under predetermined magnetic field application conditions.

  The infrared heating means 9 is provided on the downstream side of the magnetic field applying means 5 and is disposed so as to pass through the current collector foil 6 to the center of the infrared heating means 9, and the deposited layer of the electrode mixture powder 7 by infrared (IR) irradiation. It is a heating means for heating.

  The hot press means 10 is a roll-type pressure forming means provided on the downstream side of the infrared heating means 9 and has a plurality of rotatable pressure rollers (in this embodiment, two upper and lower rollers). The hot press means 10 is capable of heating and pressing in the thickness direction by inserting the current collector foil 6 on which the deposited layer of the electrode mixture powder 7 is formed between two upper and lower pressure rollers. Processing is possible. Specifically, the hot press means 10 rotates the pressure rolls in opposite directions while sandwiching the current collector foil 6 on which the deposited layer of the electrode mixture powder 7 is formed between the pressure rolls. However, the thickness and density (electrodes) of the electrode mixture layer 8 on the current collector foil 6 discharged from the downstream side of the hot press means 10 by performing a roll press process under predetermined hot press conditions (heating temperature and press pressure). Density) can be adjusted as appropriate.

Next, the manufacturing method of the battery electrode which concerns on one Embodiment of this invention using the electrode manufacturing apparatus 1 mentioned above is demonstrated.
In addition, although the manufacturing method of the battery electrode demonstrated in this embodiment is not specifically limited, the negative electrode (negative electrode sheet) which a nonaqueous electrolyte secondary battery (for example, lithium ion secondary battery) has is manufactured. Is applicable.

[Method for producing battery electrode]
The manufacturing method of the battery electrode according to the present embodiment supplies the electrode mixture powder 7 obtained by granulating the electrode mixture onto the current collector foil 6 and presses (compression molding) the sheet. As shown in FIG. 2, a paste production step S10, a granulation step S20, a supply step S30, a flattening step S40, a magnetic field application step S50, a heating step S60, and a hot press, as shown in FIG. It mainly has process S70 and is performed in this order. Below, each said process is demonstrated.
The magnetic field application step S50 can be omitted depending on the required performance of the battery electrode to be manufactured.

  The paste manufacturing step S10 is performed at a predetermined mixing ratio and solid content ratio using an electrode mixture component including a negative electrode active material (in this embodiment, graphite), a binder (binder) and the like and a solvent for dispersing the component. This is a step of producing an electrode mixture paste. Paste preparation process S10 is a process for preparing the electrode mixture paste used by granulation process S20.

  The negative electrode active material is not particularly limited as long as it can use an active material having the characteristics of occluding lithium ions during charging and releasing lithium ions during discharging. Examples of the material having such characteristics include lithium metal, carbon materials such as graphite and amorphous carbon, and the like. Among them, it is preferable to use a carbon material having a relatively large voltage change with the charging / discharging of lithium ions. A frequently used material is a powdered carbon material made of graphite or the like. In particular, graphite particles can be preferably used as in this embodiment. And the particle | grains of a negative electrode active material are tied together using the said binder.

  The binder (binder) plays a role of connecting the particles of the negative electrode active material, and includes polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR). Fluorine-containing resins such as fluororubber, and thermoplastic resins such as polypropylene can be used.

In the granulation step S20, a predetermined drying / magnetic field applying means (for example, a hot air drying furnace provided with a magnetic field applying means in the furnace) is applied to the electrode mixture paste containing graphite prepared in the paste preparation step S10. ) To obtain the electrode mixture powder 7 composed of the granulated particles 20 by drying (granulation) while applying a magnetic field at a predetermined drying temperature and magnetic field application conditions. That is, in the granulation step S20, electrode mixture powder 7 containing magnetically oriented graphite as shown in FIG. 3 can be obtained by granulating the electrode mixture paste in a magnetic field applied state. . Specifically, in the granulating step S20, an electrode mixture paste is prepared using an electrode mixture component such as a negative electrode active material (in this embodiment, graphite), a binder (binder), and a solvent for dispersing the component. Prepared, dried (granulated) to obtain a dried product, pulverized and classified to the dried product, and granulated particles 20 having a predetermined particle diameter, bulk density and other properties It is a process of producing.
In addition, the paste preparation process S10 and granulation process S20 mentioned above become a preparatory process for starting manufacture of the electrode for batteries by the electrode manufacturing apparatus 1. FIG.

  In addition, as the graphite contained in the granulated particles 20 constituting the electrode mixture powder 7 in the granulating step S20, elongated graphite is used. More specifically, the graphite to be used is preferably graphite particles, and the shape of the graphite particles is not a spherical shape but an elongated shape such as an ellipse or a scale. Further, in the case of elliptical graphite and scaly graphite, graphite particles having a large particle size are preferable. Specifically, the particle size in the longitudinal direction of the graphite particles is equal to or less than the film thickness of the electrode mixture layer 8 after pressing. Is preferably used. Details of the graphite particle shape will be described later.

  In the supplying step S30, the electrode mixture powder 7 obtained in the granulating step S20, that is, the granulated particles 20 in which the graphite is constituted as primary particles is supplied onto the current collector foil 6 by the powder molding apparatus 2. In both cases, the electrode mixture powder 7 is formed as a deposited layer on the current collector foil 6.

  In the flattening step S40, the electrode mixture powder 7 supplied onto the current collector foil 6 by the powder molding apparatus 2 is flattened using the flattening blade 4 so that the surface is uniform, and the tip of the flattening blade 4 is obtained. And a deposited layer of the electrode mixture powder 7 having the same thickness as that between the surface of the current collector foil 6 and the surface of the current collector foil 6.

In the magnetic field application step S50, the magnetic layer applying means 5 applies the deposited layer of the electrode mixture powder 7 flattened by the flattening blade 4 to the thickness direction of the deposited layer of the electrode mixture powder 7 (current collecting foil 6). This is a step of applying a magnetic field (magnetic force) along a direction perpendicular to the vertical direction in FIG. Specifically, in the magnetic field application step S50, a magnetic field is further applied to the deposited layer of the electrode mixture powder 7 formed on the current collector foil 6 before the hot pressing step that is a subsequent step of the magnetic field application step S50. This is a step of controlling the orientation of the electrode mixture powder 7 (granulated particles 20 in which graphite is magnetically oriented) substantially perpendicularly to the current collector foil 6 by application. More specifically, as shown in FIG. 4, in the magnetic field application step S50, each of the granulated particles 20 constituting the deposited layer of the electrode mixture powder 7 and in which the graphite is magnetically oriented is subjected to a magnetic field again. This is a step of standing substantially perpendicular to the surface of the current collector foil 6 by applying.
The magnetic field application step S50 can be omitted depending on the required performance of the battery electrode to be manufactured, but the graphite is oriented substantially perpendicular to the current collector foil 6 through the magnetic field application step S50. Therefore, pressure is preferentially applied to the graphite oriented at the time of pressing in the hot press step S70, the electrode mixture is not easily crushed, the electrode mixture layer 8 can be kept at a lower density, and more exfoliated. Strength is improved.

  The heating step S60 is a step of heating the deposited layer of the electrode mixture powder 7 at a predetermined temperature by infrared (IR) irradiation by the infrared heating means 9. In heating process S60, the heat | fever is added to the binder (binder) in the granulated particle 20 which comprises the electrode mixture powder 7, thereby increasing the adhesiveness of the granulated particles 20 and the fluidity of the granulated particles 20. Can be suppressed.

In the heat press step S70, after heating by the infrared heating means 9, a predetermined hot press condition (heating temperature and press) is applied to the current collector foil 6 on which the deposited layer of the electrode mixture powder 7 is deposited on the surface. This is a step of forming an electrode mixture layer 8 that is thinner than the deposited layer of the electrode mixture powder 7 by hot pressing under pressure. In this way, a negative electrode (negative electrode sheet) in which the electrode mixture layer 8 is formed on the current collector foil 6 by powder molding is produced.
Next, while following each process of the manufacturing method of the said battery electrode, the Example which manufactured the negative electrode (negative electrode sheet) as a battery electrode using the electrode manufacturing apparatus 1 mentioned above, and a comparative example are given, and this invention is given. explain.

[Example 1]
(Paste making process S10)
First, a negative electrode active material (in this example, graphite), a binder (binder) made of styrene-butadiene copolymer (SBR), and a binder (binder) made of carboxymethylcellulose (CMC). Various electrode mixture components were mixed at a mixing ratio of 96: 3.3: 0.7, dispersed in a predetermined dispersion medium (N-methyl-2-pyrrolidone (NMP) in this example), and fixed. An electrode mixture paste was prepared so that the fraction was 50%.

(Granulation step S20)
Next, the electrode mixture paste obtained in the paste preparation step S10 is dried at a drying temperature (hot air temperature) of 110 ° C. by means of drying / magnetic field applying means (in this embodiment, a hot air drying furnace provided with a magnetic field applying means in the furnace). Then, drying (granulation) was performed while applying a magnetic field for a predetermined time under a magnetic force of 1.2 T to obtain a dried product (untreated granulated particles) (see FIG. 5). In FIG. 5, it can be confirmed that the plurality of graphite particles are oriented in the same direction (vertical direction in FIG. 5). Then, the granulated particles 20 are produced by crushing and classifying the dried product by a predetermined appropriate means, and a desired average particle size (particle size D50 after granulation in this example D15 = 15 μm). And granulated particles 20 were produced as secondary particles having a particle size distribution.
In addition, as a method of heating (baking), it is not limited to the said hot air drying furnace, The well-known method which can apply the heat to electrode mixture and can produce the granulated particle 20 is applicable. Moreover, as a method for crushing, a known method such as a ball mill can be applied.
The drying temperature (hot air temperature) is preferably lower than the glass transition temperature of the granulated particles 20 and close to the glass transition temperature in view of drying efficiency. In this embodiment, it is preferable to dry in the temperature range of 80 to 130 ° C.

(Supply process S30)
The electrode mixture powder 7 composed of the granulated particles 20 obtained in the granulation step S20 is fed to the supply device of the powder molding apparatus 2, and is conveyed by the conveying means 3 from the supply port of the powder molding apparatus 2. An electrode mixture powder 7 is supplied onto the current collector foil 6.

(Planarization step S40)
Next, the electrode mixture powder 7 supplied onto the current collector foil 6 by the powder molding apparatus 2 is flattened using the flattening blade 4 so that the surface is uniform, and the tip of the flattening blade 4 and the current collector are collected. A deposited layer of the electrode mixture powder 7 having the same thickness as that between the surfaces of the foil 6 was formed.

(Magnetic field application step S50)
Next, with respect to the deposited layer of the electrode mixture powder 7 flattened by the planarizing blade 4, the magnetic field applying means 5 applies the thickness direction of the deposited layer of the electrode mixture powder 7 (with respect to the current collector foil 6). A magnetic field (magnetic force) along the vertical direction (vertical direction in FIG. 1) was applied. As application conditions of the magnetic field (magnetic force), the magnetic field intensity was 0.25 T, and the magnetic field application time was 0.5 sec or more.

(Heating step S60)
Subsequently, the deposited layer of the electrode mixture powder 7 was infrared (IR) heated (heating temperature: 200 ° C.) by the infrared heating means 9.

(Hot press process S70)
Subsequently, after heating by the infrared heating means 9, the current collector foil 6 on which the deposited layer of the electrode mixture powder 7 is deposited is hot-pressed by the hot press means 10 to deposit the electrode mixture powder 7. A thinner electrode mixture layer 8 was formed. In this manner, a negative electrode (negative electrode sheet) in which the electrode mixture layer 8 composed of the granulated particles 20 was formed on the current collector foil 6 by powder molding was produced.
Then, after adjusting the size of the electrode so that the design capacity of the battery becomes a predetermined value, the negative electrode (negative electrode sheet) described above and a predetermined positive electrode (positive electrode sheet) prepared in advance are made to face each other via a separator. The evaluation battery of Example 1 was produced as a laminated cell type lithium ion secondary battery by forming a body and sealing the laminate together with the electrolyte.
Incidentally, the predetermined positive (positive electrode sheet), which was prepared by a known production method, the positive electrode active material (the present embodiment, lithium nickel composite oxide (LiNiO _2), lithium manganese composite oxide (LiMnO ₂ ), Cobalt lithium composite oxide (LiCoO ₂ ) ternary lithium-containing composite oxide), conductive material made of acetylene black (AB), and binder (binder) made of polyvinylidene fluoride (PVDF) 3 An electrode mixture component is mixed in a predetermined weight ratio and dispersed in a predetermined dispersion medium (N-methyl-2-pyrrolidone (NMP) in this embodiment) to prepare an electrode mixture paste, and an electrode The mixture paste was applied to a current collector foil (aluminum foil) and dried.

[Example 2]
A negative electrode (negative electrode sheet) for comparative evaluation was produced in the same procedure as in Example 1 except that the magnetic field applying step S50 was omitted in the manufacturing process of Example 1 (no magnetic field was applied by the magnetic field applying means 5). did. Moreover, the evaluation battery of Example 2 was produced in the same procedure as Example 1 using the said negative electrode (negative electrode sheet).

[Comparative example]
As shown in Patent Document 1, a negative electrode (negative electrode sheet) was produced by a conventional powder molding method (without magnetic field orientation of graphite) using granulated particles that were not magnetically oriented during granulation. That is, a negative electrode (negative electrode sheet) for comparative evaluation was produced in the same procedure as in Example 1 except that the magnetic field was not applied in the granulating step S20 and the magnetic field applying step S50 in the manufacturing process of Example 1. Moreover, the evaluation battery of the comparative example was produced in the same procedure as Example 1 using the said negative electrode (negative electrode sheet).

[Measurement of IV resistance (initial resistance)]
About each said evaluation battery, the SOC (State of Charge) of each evaluation battery is 60% by carrying out constant current charge with the electric current value equivalent to 60% of initial capacity from the state after discharge at the electric current value of 1 / 5C. Prepared. In SOC 60%, the constant voltage of 1 / 3C, 1C, 3C is flowed for 5 seconds to measure the overvoltage during charging and discharging, and the average value of resistance calculated by dividing those values by the current value is the initial value DC resistance of All the operations described above were performed in an environment of 25 ° C.

<About the effect of the present invention>
In FIG. 6, the electrode structure of each negative electrode in Example 1 and a comparative example (without magnetic field orientation of graphite) is shown. (A) shows the negative electrode produced as a comparative example, (b) is the negative electrode produced in Example 1. Although Example 1 and Comparative Example were hot pressed under the same hot press conditions, Example 1 was able to obtain a lower density electrode mixture layer than Comparative Example. . This is because the orientation of graphite in each granulated particle constituting the electrode mixture powder is uniform (the void in each granulated particle constituting the electrode mixture powder is reduced), so that it is preferential to the oriented graphite during pressing. This is because pressure is applied to the electrode mixture, the electrode mixture is not easily crushed, and the electrode mixture layer 8 can be kept at a low density. In other words, a desired electrode density can be maintained even with high-pressure pressing, and in addition, a high peel strength can be obtained. Furthermore, in Example 1, the peel strength is improved compared to Example 2 (see the results of a peel strength test described later and FIG. 9). This is because Example 1 was oriented substantially perpendicular to the current collector foil 6 by applying a magnetic field to the granulated particles 20 constituting the electrode mixture powder 7 in the magnetic field application step S50 (see FIG. 4). This is because excessive crushing and densification by hot pressing can be further prevented as compared with Example 2 in which the magnetic field application step S50 is omitted. Moreover, since the oriented granulated particles 20 stably maintain the film structure (electrode mixture layer structure), the film structure becomes strong and high peel strength can be obtained. In particular, as in Example 1, the granulated particles 20 oriented substantially perpendicular to the current collector foil 6 ensure a conductive path in the thickness direction of the electrode mixture layer 8, and thus the conductivity of the electrode. Can be improved. For this reason, the resistance reduction effect is also acquired as battery performance.

<Relationship between graphite orientation and IV resistance>
The IV resistance was measured for each of the evaluation batteries of Examples 1 and 2 and the comparative example.
FIG. 7 shows the relationship between the degree of graphite orientation (degree of magnetic field orientation) and IV resistance (initial resistance of a lithium secondary battery).
The “applied electrode” in FIG. 7 has the same electrode material composition as in Example 1, but an electrode mixture paste was applied and dried to produce a negative electrode (negative electrode sheet). An evaluation battery was produced in the same procedure. Moreover, the numerical value in the parenthesis described under the comparative example and coating electrode in FIG. 7 is a value of the degree of graphite orientation.

  In FIG. 7, the vertical axis is the (110) / (002) intensity ratio using the peak intensity of the crystal plane (110) and the peak intensity of the crystal plane (002), as measured by powder X-ray diffraction measurement, and the horizontal axis is IV resistance (initial resistance) [Ω]. The higher the (110) / (002) strength ratio (the more it goes in the upward direction in FIG. 7), the higher the orientation (in this embodiment, in the granulating step 20 in the same direction in the granulated particles 20). The graphite is aligned along the magnetic field application step S50 and is aligned along the substantially vertical direction with respect to the current collector foil 6). More specifically, even if the (110) / (002) intensity ratio is about 0.02 or more, it can be said that the film is in a highly oriented state. Further, the present invention is not limited to the above production conditions of the present embodiment, but depends on the electrode material (electrode mixture component) to be used, the size / shape of graphite (aspect ratio, etc.), various production conditions, etc. Thus, the magnetic field strength and the magnetic field application time may be set as appropriate. As is clear from FIG. 7, each IV resistance in the evaluation batteries of Examples 1 and 2 was smaller than each IV resistance in the evaluation battery and the coated electrode of the comparative example. This means that the electrode structure of the negative electrode (negative electrode sheet) produced in Examples 1 and 2 has approached the ideal electrode structure shown in FIG. From the results shown in FIG. 7 as described above, it was confirmed that the IV resistance could be reduced in the lithium ion secondary battery using the negative electrode (negative electrode sheet) manufactured by the manufacturing method of the above embodiment.

<Relationship between peak intensity ratio and graphite particle shape>
FIG. 8 shows the relationship between the degree of graphite orientation ((110) / (002) strength ratio) and the shape of graphite particles. In FIG. 8, the horizontal axis represents the (110) / (002) intensity ratio using the peak intensity of the crystal plane (110) and the peak intensity of the crystal plane (002) as measured by powder X-ray diffraction measurement. It is shown that the orientation is smaller as it goes to the left and the orientation is larger as it goes to the left side of the horizontal axis. As described above, the graphite used in the present invention is preferably graphite particles, and the graphite particles have an elongated shape such as an elliptical shape or a scale shape instead of a spherical shape. Further, in the case of elliptical graphite and scaly graphite, graphite particles having a large particle size are preferable. Specifically, the particle size in the longitudinal direction of the graphite particles is equal to or less than the film thickness of the electrode mixture layer 8 after pressing. Is preferably used. That is, as graphite used in the present invention, spherical graphite (artificial graphite, carbon) shown on the right side of FIG. 8 is not suitable. On the other hand, the aspect ratio of the particle size in the longitudinal direction of the graphite particles and the particle size (or particle thickness) in the short direction perpendicular thereto (longitudinal particle size / short particle size (particle thickness) S)) is a long and narrow particle shape (that is, a particle shape having shape anisotropy) larger than 1, such as spherical graphite (center of FIG. 8), scale-like graphite (left side of FIG. 8), etc. Therefore, it has the orientation which orients so that the longitudinal direction of particle | grains may become in parallel with a magnetic field application direction by application of a magnetic field. Therefore, spherical graphite and scaly graphite having particle shapes having shape anisotropy are suitable as graphite used in the present invention. On the other hand, when viewed in terms of the degree of graphite orientation ((110) / (002) strength ratio), the graphite used in the present invention is in a powder state when subjected to a magnetic field orientation at 0.25 T for 1 sec or more, The peak intensity ratio (110) / (002) of the X-ray analysis at that time is 0
. Graphite having a peak strength ratio (110) / (002) of 0.07 or more is preferable.

<Peel strength test>
The peel strength of each electrode mixture layer of Examples 1 and 2 and Comparative Example was evaluated using a commercially available tensile tester. The evaluation results are shown in FIG.
In addition, about the test piece of Examples 1, 2 and the comparative example used in the peel strength test, it was produced by the method for manufacturing each battery electrode of Examples 1, 2 and Comparative Example shown above, The hot press conditions were adjusted to produce the same predetermined electrode density (the density of the electrode mixture layer).
The negative electrode sheets of Examples 1 and 2 and Comparative Example prepared above were cut into a predetermined shape, and three test pieces were prepared. And this test piece was fixed to the mount frame of the tensile tester. At this time, the current collector foil was fixed to the mount so that the electrode mixture layer was on the upper side in the vertical direction. Then, attach one side of the double-sided tape to the lower end of the tension jig, attach the other side to the electrode mixture layer, and pull the tension jig upward at a predetermined speed to the electrode mixture layer. Was peel strength (tensile strength) [N / m] when peeled from the current collector foil. And the average value of peeling strength of Example 1, 2 and a comparative example was calculated | required using the measured value of the test piece of 3 pieces each of Example 1, 2 and a comparative example. The measurement results are shown in FIG. In FIG. 9, in order to strictly compare the peel strength, the electrode densities of Examples 1 and 2 and the comparative example are made to be the same as described above. As can be seen from FIG. 9, in Examples 1 and 2 in which graphite is magnetically oriented, the peel strength is markedly improved compared to the comparative example. Moreover, when Example 1 and Example 2 are compared, compared with Example 2 which applied the magnetic field only once at the time of granulation process S20, a magnetic field is applied once in the granulation process S20, and also magnetic field application process S50. In this case, it was confirmed that the peel strength was further improved in Example 1 in which the second magnetic field was applied.

  As described above, the present invention provides a battery electrode for forming an electrode by supplying and pressing a powdered electrode mixture obtained by granulating an electrode mixture onto a current collector foil. In the manufacturing method, an electrode mixture powder is obtained by granulating the electrode mixture containing graphite and applying a magnetic field to the electrode mixture containing the graphite. Is formed on the current collector foil, and the electrode is formed by the pressing. As a result, the orientation of graphite in each granulated particle constituting the electrode mixture powder is uniform (the void in each granulated particle constituting the electrode mixture powder is reduced), so it is preferential to the graphite oriented during pressing. Pressure is applied to the electrode mixture, and the electrode mixture is not easily crushed, and the electrode mixture layer can be kept at a low density. That is, a desired electrode density can be maintained even when high-pressure pressing is performed, and the peel strength is also improved.

  The present invention produces granulated particles which are secondary particles having orientation by orienting the magnetic field during granulation, and the current of the current collector foil is obtained by reorienting the powder comprising the granulated particles again before press molding. It is possible to obtain an electrode made of granulated particles oriented substantially perpendicular to the above.

DESCRIPTION OF SYMBOLS 1 Electrode manufacturing apparatus 5 Magnetic field application means 6 Collective foil 7 Electrode mixture powder 8 Electrode mixture layer 10 Hot press means 20 Granulated particle

Claims (3)

In the method for producing an electrode for a battery for forming an electrode by supplying an electrode mixture powder obtained by granulating an electrode mixture onto a current collector foil and pressing it,
Including graphite in the electrode mixture;
A method for producing a battery electrode, wherein the electrode mixture powder is obtained by drying and granulating the electrode mixture containing graphite while applying a magnetic field.   After supplying the electrode mixture powder onto the current collector foil, the electrode mixture powder is applied to the current collector foil by further applying a magnetic field to the current collector foil before performing the pressing. The method for producing a battery electrode according to claim 1, wherein the orientation is controlled substantially vertically.   A battery electrode manufactured by the method for manufacturing a battery electrode according to claim 1.

Images