JP2017134911A - Method for manufacturing electrode for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce surface defects in an electrode for a battery, which is manufactured by rolling a granulated material.SOLUTION: A method for manufacturing an electrode for a battery comprises the steps of: (S01) preparing a complex including an electrode active material and carbon black by mixing the electrode active material and the carbon black with a resonance mixer; (S02) preparing a granulated material by mixing the complex, a binder and a solvent; and (S03) manufacturing an electrode for a battery, which includes the granulated material. The step (S03) of manufacturing an electrode for a battery includes: rolling the granulated material; and putting the granulated material on the surface of an electrode current collector. In the step (S01) of preparing a complex, the input acceleration of the resonance mixer is 50-100 G, and a mixing time is 90-1,800 seconds.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for manufacturing a battery electrode.

  JP-A-2015-174024 (Patent Document 1) includes three rolls arranged in parallel, and the granulated body can be rolled in the first roll gap and rolled in the second roll gap. A battery electrode manufacturing apparatus configured to transfer the granulated body to a substrate is disclosed.

JP-A-2015-174024

  The granulated body is an aggregate (granular body) of composite particles (hereinafter referred to as “granulated particles”) including an electrode active material, a conductive material, a binder, and the like. Patent Document 1 proposes a method of manufacturing a battery electrode by rolling the granulated body into a sheet shape with a roll gap and further transferring it to a base material (current collector).

  However, since the extensibility of the granulated material is not sufficient, the granulated material may be broken during rolling and transfer, and surface defects such as pinholes and streaks may occur in the manufactured electrode.

  The present inventor obtained an idea that it is effective to improve the solvent retention ability of the granulated particles (hereinafter referred to as “liquid retention”) in order to improve the spreadability of the granulated particles. A means to materialize this idea was examined. As a result, the present inventors have found that the liquid retention of the granulated particles is significantly improved by preparing a composite containing an electrode active material and carbon black before forming the granulated particles. The present invention has been completed.

That is, the battery electrode manufacturing method of the present invention includes a step of preparing a composite containing the electrode active material and the carbon black by mixing the electrode active material and carbon black using a resonance mixer;
Preparing a granulated body by mixing the composite, binder and solvent;
Producing a battery electrode including the granulated body.
The step of producing the battery electrode includes rolling the granulated body and disposing the granulated body on the surface of the electrode current collector.
In the step of preparing the composite, the input acceleration of the resonant mixer is 50 G or more and 100 G or less, and the mixing time is 90 seconds or more and 1800 seconds or less.

  “Carbon black” is carbon fine particles used as a conductive material for electrodes. Carbon black has a plurality of structures such as a bunch of grapes in which spherical primary particles (called “domains”) are connected. This partial structure is referred to as an “aggregate”, and the entire structure including a plurality of aggregates is referred to as a “structure”. The size (spread) of the structure is evaluated by the amount of oil absorption. The “oil absorption amount” is an index value indicating how much oil (organic solvent) can be absorbed and retained in the gap formed by the aggregate.

  In the granulated particles containing carbon black, it is considered that carbon black plays a part of the liquid retention of the granulated particles. That is, carbon black retains the organic solvent in the gaps between the aggregates, thereby imparting liquid retention to the granulated particles. However, according to the conventionally known mixing means, the aggregate aggregates or the structure is destroyed, and the desired liquid retention (oil absorption amount) is not exhibited.

  Therefore, in the manufacturing method of the present invention, an electrode active material and carbon black are mixed in advance using a resonance mixer, and these are combined. Here, the “resonant mixer” is a mixer that vibrates and stirs an object by inducing resonance vibration in the object. According to the inventor's research, by using a resonant mixer, aggregation of aggregates can be crushed in carbon black without destroying the structure.

  FIG. 1 is a first conceptual diagram showing a composite containing an electrode active material and carbon black. The composite 10A is formed when the electrode active material 1 and the carbon black 2A are combined using a resonant mixer. In the composite 10 </ b> A, the carbon black 2 </ b> A is uniformly attached to the surface of the electrode active material 1. In the carbon black 2A, aggregates do not aggregate and many voids are formed between the aggregates. That is, the carbon black 2A maintains the structure. Thus, it is considered that the solvent 3 can be held in the gap. Further, it is considered that a good electron conduction path is formed on the surface of the electrode active material by having a large contact area between the electrode active material 1 and the carbon black 2A and maintaining the structure. Thereby, reduction of battery resistance can be expected.

  FIG. 2 is a second conceptual diagram showing a composite containing an electrode active material and carbon black. The composite 10B is formed when the electrode active material 1 and the carbon black 2B are simply stirred and mixed by, for example, a mixer using stirring blades. In the composite 10B, the structure of the carbon black 2B can be maintained, but aggregates included in the structure are aggregated. Therefore, it is considered that the solvent cannot be retained in the complex 10B unlike the complex 10A described above. Further, it is considered that a continuous electron conduction path cannot be formed because the amount of carbon black 2B present on the surface of the electrode active material 1 is small.

  FIG. 3 is a third conceptual diagram showing a composite containing an electrode active material and carbon black. The composite 10C is formed when the electrode active material 1 and the carbon black 2C are combined by a so-called mechanochemical method. The “mechanochemical method” is a method in which particles are combined with each other by mechanical energy such as impact, friction, and compression generated during the pulverization process of solid particles. In the composite 10 </ b> C, the carbon black 2 </ b> C is uniformly attached to the surface of the electrode active material 1. Therefore, it is considered that an electron conduction path is easily formed. However, it is considered that the solvent cannot be retained because the structure of the carbon black 2C is destroyed.

  As described above, a granulated body made of granulated particles having high liquid retention can be formed by adding a binder and a solvent to the composite 10A composited by the resonance mixer and granulating.

  Granulated particles having high liquid retention properties tend to be excellent in spreadability. It is considered that the solvent held in the granulated particles promotes slipping between the particles contained in the granulated particles and the granulated particles become soft. By rolling a granulated body containing granulated particles rich in spreadability, it is possible to produce a battery electrode while suppressing the occurrence of surface defects (such as streaks and pinholes).

  However, when the resonant mixer is used, the input acceleration is set to 50 G to 100 G, and the mixing time is set to 90 seconds to 1800 seconds. This is because, when either one of the input acceleration and the mixing time is out of these ranges, the effect of improving the liquid retention property may be reduced. Here, the “input acceleration” indicates the acceleration of vibration input to the object (electrode active material and carbon black).

  According to the above, surface defects can be reduced in the battery electrode produced by rolling the granulated body.

It is a 1st conceptual diagram which shows the composite_body | complex which concerns on embodiment of this invention. It is a 2nd conceptual diagram which shows the composite_body | complex which concerns on a reference form. It is a 3rd conceptual diagram which shows the composite_body | complex which concerns on a reference form. It is a flowchart which shows the outline of the manufacturing method of the battery electrode which concerns on embodiment of this invention. It is the schematic which shows an example of an electrode manufacturing step. It is a figure which shows the oil absorption amount of the composite_body | complex which concerns on an Example and a comparative example. It is a figure which shows the number of surface defects of the battery electrode which concerns on an Example and a comparative example. It is a figure which shows the relationship between the compounding quantity of carbon black, and the internal resistance of a battery.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described. However, this embodiment is not limited to the following description. In the following description, the battery electrode may be abbreviated as “electrode”. In the following description, an example of application to the positive electrode is mainly shown, but the present embodiment can also be applied to the negative electrode. Furthermore, in the following description, application examples mainly to electrodes for lithium ion batteries are shown, but it is also possible to manufacture battery electrodes other than lithium ion batteries according to this embodiment.

<Method for producing battery electrode>
FIG. 4 is a flowchart showing an outline of the electrode manufacturing method of the present embodiment. The manufacturing method of this embodiment includes a composite preparation step (S01), a granule preparation step (S02), and an electrode manufacturing step (S03). Hereinafter, each step will be described.

<< Composite Preparation Step (S01) >>
In the composite preparation step, a composite containing the electrode active material and the carbon black is prepared by mixing the electrode active material and the carbon black using a resonance mixer.

(Electrode active material)
The electrode active material is not particularly limited. Examples of the electrode active material include lithium (Li) -containing metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , and LiFePO ₄ , and mixtures thereof. Can be mentioned. The d50 of the electrode active material (d50 of the secondary particles) is, for example, about 2 to 20 μm. Here, “d50” in the present specification indicates a particle size of 50% cumulative from the fine particle side in the volume-based particle size distribution measured by the laser diffraction / scattering method.

(Carbon black)
Examples of carbon black include acetylene black, thermal black, channel black, furnace black, lamp black, and the like, and mixtures thereof. From the viewpoint of the amount of oil absorption, the carbon black is preferably acetylene black. It is preferable that d50 of carbon black (d50 of primary particles) is smaller than d50 of the electrode active material. The d50 of the primary particles is, for example, about 10 nm to 1 μm.

  The compounding amount of carbon black is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the electrode active material. This is because the effect of reducing the battery resistance is large within this range. From the viewpoint of resistance reduction effect and battery capacity, the blending amount is more preferably 1 part by mass or more and 20 parts by mass or less, and still more preferably 1 part by mass or more and 10 parts by mass or less.

(Resonant mixer)
As the resonance mixer, for example, a product name “LabRAM series” manufactured by Resodyn, etc., and a device having the same function can be used. The input acceleration in the resonant mixer is 50 G or more and 100 G or less, and the mixing time is 90 seconds or more and 1800 seconds or less.

  When the input acceleration is less than 50 G, aggregates may aggregate and desired liquid retention properties may not be obtained. Moreover, since sufficient compounding is performed with an input acceleration of 100 G, it is uneconomical if it exceeds 100 G.

  If the mixing time is less than 90 seconds, the aggregate may aggregate and the desired liquid retention may not be obtained. If the mixing time exceeds 1800 seconds, the structure may be destroyed and the liquid retention may be reduced.

  The composite 10A shown in FIG. 1 can be prepared by performing the composite under conditions where the input acceleration is 50 G or more and 100 G or less and the mixing time is 90 seconds or more and 1800 seconds or less. In the composite 10A, the carbon black 2A is adhered to the surface of the electrode active material 1 and the structure is maintained. Further, since the structure is maintained, a good electron conduction path is formed, and a reduction in battery resistance can be expected.

<< Granulate preparation step (S02) >>
In the granule preparation step, a granule is prepared by mixing the composite (electrode active material and carbon black), binder and solvent.

(Granulating device)
For the preparation of the granulated body, a conventionally known stirring granulator or the like can be used. A granulated body can be prepared by stirring and mixing a composite, a binder, and a solvent using an agitation granulator.

(Binder)
The binder is not particularly limited. Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), carboxymethylcellulose (CMC), and the like, and mixtures thereof.

(solvent)
The solvent is appropriately selected in consideration of the dispersibility and solubility of the binder. The solvent is typically an organic solvent such as N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), dimethylformamide (DMF), and the like. However, in this embodiment, the use of water as a solvent is not excluded. For example, if the carbon black has been subjected to a hydrophilic treatment (for example, an oxidation treatment), it is considered that water can be retained in the gaps between the aggregates.

  The solid content rate in the granule preparation step is, for example, about 65 to 85% by mass (typically about 75% by mass). A solid content rate shows the mass ratio which components other than a solvent occupy in a granule. In this embodiment, since the carbon black structure is maintained in the composite, a solvent is held in the structure, and granulated particles having high liquid retention can be formed. The solid content of the granulated material is, for example, about electrode active material: 69 to 98% by mass, carbon black: 1 to 30% by mass, and binder: about 1 to 10% by mass.

  The shape of the granulated particles constituting the granulated body is not particularly limited. The shape of the granulated particles may be, for example, a block shape or a substantially spherical shape. After the agitation granulation, the granulated particles may be formed by further extrusion granulation or the like. That is, the shape of the granulated particles may be, for example, a cylindrical shape. The granulation conditions are appropriately adjusted according to the size of the intended granulated particles. The d50 of the granulated particles is, for example, about 500 μm to 1 mm.

<< Electrode manufacturing step (S03) >>
In the electrode manufacturing step, a battery electrode including a granulated body is manufactured. The step includes rolling the granulated body (rolling operation) and disposing the granulated body on the surface of the electrode current collector (arranging operation). As described below, one aspect of “arranging” includes “transferring”. The rolling operation and the arranging operation may be executed in this order, may be performed in sequence, or may be performed simultaneously.

(Electrode manufacturing equipment)
FIG. 5 is a schematic diagram illustrating an example of an electrode manufacturing step. The electrode manufacturing apparatus 90 shown in FIG. 5 includes three rolls, that is, an A roll 91, a B roll 92, and a C roll 93. Each roll is rotationally driven by a driving device (not shown). The curved arrows drawn on each roll indicate the rotation direction of each roll.

  The granulated body 20 </ b> A (granular body) is supplied to the gap between the A roll 91 and the B roll 92. A predetermined load is applied to the A roll 91. In the gap between the A roll 91 and the B roll 92, the granulated body 20A is rolled and formed into a sheet-like granulated body 20B.

  The granulated body 20 </ b> B (sheet body) is conveyed by the B roll 92 and supplied to the gap between the B roll 92 and the C roll 93. The electrode current collector 11 is conveyed by the C roll 93 and supplied to the gap between the B roll 92 and the C roll 93. The electrode current collector 11 is a metal foil such as an aluminum (Al) foil.

  In the gap between the B roll 92 and the C roll 93, the granulated body 20 </ b> B is pressed against the electrode current collector 11. Thereby, the granulated body 20B is pressure-bonded to the electrode current collector 11, and the granulated body 20B is disposed on the surface of the electrode current collector 11. That is, the granulated body 20 </ b> B is transferred from the surface of the B roll 92 to the surface of the electrode current collector 11.

  In this embodiment, the liquid retention property of the granulated particle which comprises a granulated body is high. Therefore, the granulated particles are excellent in spreadability. Therefore, when the granulated body 20A (granular body) is rolled and when the granulated body 20B (sheet body) is transferred, problems such as breaking of the granulated particles are suppressed. That is, surface defects such as pinholes and streaks are reduced in the electrode after the granulated body is transferred.

  By disposing the granulated body 20B on the surface of the electrode current collector 11, the granulated body 20B becomes an electrode mixture layer. Thereafter, an operation of evaporating the solvent remaining in the granulated body 20B (electrode mixture layer) may be performed. The evaporation operation of the solvent can be performed by a drying furnace (not shown). Furthermore, the battery electrode can be manufactured by performing compression, cutting, or the like according to the specification of the battery.

  In FIG. 5, the granule 20 </ b> B is arranged on one surface of the electrode current collector 11, but the granule is arranged on both surfaces of the electrode current collector 11 by repeating the same operation. You can also.

  Hereinafter, although this embodiment is described using an example, this embodiment is not limited to the following example.

<Experiment 1: Examination of compounding method>
In Experiment 1, a composite containing an electrode active material and carbon black was prepared using various composite methods, and a battery electrode was manufactured using the composite.

<< Examples 1 to 5 (resonant mixer) >>
The following devices and electrode materials were prepared.

(apparatus)
Resonant mixer: Product name “LabRAM II”, manufactured by Resodyn Agitation granulator: Food processor, manufactured by Yamamoto Electric Electrode manufacturing apparatus: Electrode manufacturing apparatus including three rolls (see FIG. 5).

(Electrode material)
Electrode active material: Li-containing nickel cobalt manganese composite oxide (LNCM)
Carbon black: Acetylene black (AB)
Binder: PVdF
Solvent: NMP
Electrode current collector: Al foil.

Example 1
1. Complex preparation step (S01)
A composite was prepared by mixing an electrode active material (100 parts by mass) and carbon black (1 part by mass) using a resonant mixer. The resonance mixer conditions were input acceleration = 100 G and mixing time = 90 seconds. The complex prepared here corresponds to the complex 10A shown in FIG.

2. Granule preparation step (S02)
Granulation is performed by adding a composite (98 parts by mass) and a binder (2 parts by mass) to a food processor, adding a solvent so that the solid content of the granulation is 75% by mass, and mixing them. The body was prepared.

3. Electrode manufacturing step (S03)
By supplying the granulated body and the electrode current collector to the electrode manufacturing apparatus shown in FIG. 5, rolling the granulated body as described above, and placing the granulated body on the surface of the electrode current collector, the battery An electrode was manufactured.

(Examples 2 to 5)
As shown in Table 1 below, a battery electrode was produced in the same manner as in Example 1 except that the amount of carbon black was changed.

<< Comparative Examples 1-3 (Mechanochemical Method) >>
(Comparative Example 1)
1. Complex preparation step (S01)
“Nobilta” manufactured by Hosokawa Micron Co., Ltd. was prepared as a particle composite device. A composite was prepared by mixing an electrode active material (100 parts by mass) and carbon black (1 part by mass) using a particle compounding apparatus. The composite prepared here corresponds to the composite 10C shown in FIG.

2. Granule preparation step (S02)
Granulation is performed by adding a composite (98 parts by mass) and a binder (2 parts by mass) to a food processor, adding a solvent so that the solid content of the granulation is 75% by mass, and mixing them. The body was prepared.

3. Electrode manufacturing step (S03)
By supplying the granulated body and the electrode current collector to the electrode manufacturing apparatus shown in FIG. 5, rolling the granulated body as described above, and placing the granulated body on the surface of the electrode current collector, the battery An electrode was manufactured.

(Comparative Examples 2 and 3)
As shown in Table 1 below, a battery electrode was produced in the same manner as in Comparative Example 1 except that the blending amount of carbon black was changed.

<< Comparative Examples 4 to 6 (simple mixing) >>
(Comparative Example 4)
1. Complex preparation step (S01)
A composite was prepared by mixing an electrode active material (100 parts by mass) and carbon black (1 part by mass) using a food processor. The complex prepared here corresponds to the complex 10B shown in FIG.

2. Granule preparation step (S02)
Granulation is performed by adding a composite (98 parts by mass) and a binder (2 parts by mass) to a food processor, adding a solvent so that the solid content of the granulation is 75% by mass, and mixing them. The body was prepared.

3. Electrode manufacturing step (S03)
By supplying the granulated body and the electrode current collector to the electrode manufacturing apparatus shown in FIG. 5, rolling the granulated body as described above, and placing the granulated body on the surface of the electrode current collector, the battery An electrode was manufactured.

(Comparative Examples 5 and 6)
As shown in Table 1 below, a battery electrode was produced in the same manner as in Comparative Example 4 except that the amount of carbon black was changed.

<Evaluation>
1. Evaluation of Oil Absorption The oil absorption of the composites according to Example 2 and Comparative Example 5 was measured. The measurement was performed in accordance with “JIS 6217-4: 2008 Carbon black for rubber—Basic characteristics—Part 4: Determination of oil absorption (including compressed sample)”. NMP was used as the oil added to the sample. The results are shown in Table 1 below and FIG. The numerical values shown in Table 1 and FIG. 6 are relative values with the oil absorption amount of Comparative Example 5 as 100. The greater the oil absorption, the better the spreadability of the granulate.

2. Evaluation of electrode quality In the electrodes according to Example 2 and Comparative Example 5, surface defects (pinholes and stripes) included in a predetermined area were counted. Here, “pinhole” indicates a hole-like defect in which the electrode current collector can be visually recognized through the granulated body (electrode mixture layer), and “streak” indicates that the portion where the granulated body is missing Indicates an extended drawback. The results are shown in Table 1 below and FIG. The numerical values shown in Table 1 and FIG. 7 are relative values with the number of surface defects of Comparative Example 5 being 100.

3. Evaluation of electronic conductivity A battery for evaluation (lithium ion battery) was manufactured using each of the electrodes obtained above. The internal resistance of the evaluation battery was measured. The results are shown in FIG. The numerical values shown in FIG. 8 are relative values with the internal resistance of Comparative Example 4 as 100. The smaller the internal resistance, the better the battery performance.

<Discussion>
1. About Oil Absorption and Electrode Quality As shown in FIG. 6, the oil absorption of the composite is improved by 18% in Example 2 as compared with Comparative Example 5. In the composite, since the carbon black structure is maintained, it is considered that the liquid retention is improved.

  As shown in FIG. 7, the number of surface defects was reduced by about 53% in the electrode manufactured using the composite of Example 2 compared to the electrode manufactured using the composite of Comparative Example 5. Yes. Since the composite contained in the granulated particles retains the solvent, it is considered that the spreadability of the granulated particles is improved.

2. FIG. 8 is a diagram showing the relationship between the amount of carbon black blended and the internal resistance of the battery. From FIG. 8, it can be seen that when the electrode active material and carbon black are simply mixed, the internal resistance decreases in accordance with the blending amount of carbon black (Comparative Examples 4 to 6).

  When the electrode active material and carbon black are mixed by mechanochemical method, the internal resistance can be reduced as compared with the case of simple mixing (Comparative Examples 1 to 3). This is probably because carbon black can be uniformly attached to the surface of the electrode active material. However, the resistance reduction effect is saturated at 5 parts by mass. Therefore, about 5 parts by mass is expected to be the limit of compounding by the mechanochemical method.

  In Examples 1 to 5 using the resonant mixer, the internal resistance can be greatly reduced as compared with these comparative examples. It is considered that a good electron conduction path is formed by maintaining the carbon black structure.

  In the resonance mixer, a remarkable resistance reduction effect is recognized even in a region exceeding 5 parts by mass. However, it is considered that the resistance reduction effect is saturated in the region where the blending amount of carbon black exceeds 20 parts by mass. Therefore, the blending amount of carbon black is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 1 part by mass or more and 20 parts by mass or less, and still more preferably with respect to 100 parts by mass of the electrode active material. Is 1 part by mass or more and 10 parts by mass or less.

<Experiment 2: Examination of resonance conditions>
In Experiment 2, the conditions of the resonant mixer were examined in detail.

(Examples 6 and 7 and Comparative Examples 7 to 10)
As shown in Table 1, a battery electrode was produced in the same manner as in Example 2 except that the condition of the resonant mixer in the composite preparation step was changed. Further, in the same manner as in Experiment 1, the oil absorption amount of each composite and the number of surface defects of each electrode were measured. The results are shown in Table 1 above.

  As shown in Table 1, in Examples 6 and 7 in which the input acceleration is 50 G or more and 100 G or less and the mixing time is 90 seconds or more and 1800 seconds or less, an improvement in oil absorption and an improvement in electrode quality are observed. On the other hand, in Comparative Examples 7 to 10 that do not satisfy such conditions, no improvement in oil absorption and improvement in electrode quality is observed. Under the conditions of the comparative example, it is considered that aggregate aggregation or structure destruction occurs.

  Therefore, the input acceleration of the resonant mixer in the composite preparation step should be 50 G or more and 100 G or less, and the mixing time should be 90 seconds or more and 1800 seconds or less.

  The embodiments and examples disclosed herein are illustrative in all aspects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 electrode active material, 2A, 2B, 2C carbon black, 3 solvent, 10A, 10B, 10C composite, 11 electrode current collector, 20A, 20B granulated body, 90 electrode manufacturing apparatus, 91 A roll, 92 B roll, 93 C roll.

Claims (1)

Preparing a composite comprising the electrode active material and the carbon black by mixing the electrode active material and carbon black using a resonant mixer;
Preparing a granulated body by mixing the composite, binder and solvent;
Producing a battery electrode including the granulated body,
The step of manufacturing the battery electrode includes rolling the granulated body, and disposing the granulated body on a surface of an electrode current collector,
In the step of preparing the composite, the input acceleration of the resonant mixer is 50 G or more and 100 G or less, and the mixing time is 90 seconds or more and 1800 seconds or less.

Images