JP5439005B2 - Non-aqueous electrolyte storage element electrode manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an electrode constituting a nonaqueous electrolyte storage element and a nonaqueous electrolyte storage element including an electrode manufactured by the method.

  As a power source for a notebook personal computer (notebook PC) or an electric tool, there is a nonaqueous electrolyte storage element. FIG. 1 is a perspective view showing the external appearance of a nonaqueous electrolyte storage element generally called a “lithium ion secondary battery”. FIG. 2 is a cross-sectional view taken along the line aa in FIG. The electricity storage device 1 shown in these figures is a “laminate type”, and a positive electrode material 11 capable of reversibly inserting and extracting lithium ions or anions is applied on a sheet-like current collector 12. The sheet-like positive electrode 10 and the sheet-like negative electrode 20 coated with a negative electrode material 21 capable of occluding and releasing lithium ions on the sheet-like current collector 22 are also provided. The positive electrode 10 and the negative electrode 20 are arranged to face each other with the separator 50 interposed therebetween, thereby forming the power generation element 60a. In this example, the power generation element 60a is further laminated to form the electrode laminate 60.

  Tabs 40 for inputting / outputting electric power are attached to the individual current collectors (12, 22) of the positive electrode 10 and the negative electrode 20. The tabs 40 are connected by ultrasonic welding or the like in a stacked state between the positive electrodes 10 and the negative electrodes 20. And while accommodating the electrode laminated body 60 in the exterior body 30 which consists of a bag-like laminate film, while deriving the tab 40 to the exterior of the bag of the exterior body 30, the electrolysis which contains lithium salt in the exterior body 30 The laminate-type nonaqueous electrolyte storage element 1 is completed by filling the liquid and sealingly sealing the laminate film.

  In addition, a non-aqueous electrolytic storage element called a “lithium ion capacitor” of a type in which lithium ions are occluded in advance in the negative electrode 20, or the one unit of power generation element 60 a is wound into a cylinder or a rectangular cylinder, and the cylinder There is also a power storage element having a structure in which a cylindrical power generation element is inserted into a cylindrical battery can. The present invention is directed to a nonaqueous electrolyte storage element having these sheet-like electrodes.

  The sheet-like electrode, which is the main component of the nonaqueous electrolyte storage element, is manufactured by the following procedure, taking the positive electrode as an example. First, a transition metal / lithium complex oxide (for example, lithium cobaltate), which becomes a positive electrode active material, is powdered, and a binder is added to a mixture of the powdery active material and a conductive material such as carbon black, followed by stirring. Then, a slurry-like electrode material for a positive electrode is produced. Next, the slurry-like electrode material is coated on a sheet-like current collector such as a metal foil. And after drying the applied electrode material, it rolls and completes a sheet-like electrode. In addition, the technique regarding a non-aqueous-electrolyte electrical storage element is described in the following patent documents 1, for example.

JP 2008-59876 A

  In recent years, non-aqueous electrolyte storage elements are used not only as power sources for the above-mentioned notebook PCs, personal computers, power tools, etc., but also as power sources for hybrid vehicles, electric vehicles, etc. Expected. As one solution to the demand for such high output, there is a method of increasing the surface area of the active material by making the particle size of the electrode active material into “nanoparticles” of 1 μm or less.

  By the way, as shown in FIG. 3A, the nanoparticles easily aggregate even if the individual particles (primary particles) 100 are fine. In the electrode active material, the primary particles 100 are in a group. Next particles 101 are formed. On the other hand, as shown in FIG. 2B, the conductive material has a structure 201 in which primary particles 200 are aggregated in a chain shape, and each conductive material 200 is connected in contact with each other, so that the path of electrons ( A conductive path (arrow in the figure) is formed, and electrons can move between the sheet-like current collector and the electrode material applied thereon.

  Here, considering the positive electrode material using the nanoparticulated positive electrode active material, as shown in FIG. 3C, the chain-shaped conductive material 201 is formed on the secondary particles 101 of the positive electrode active material. Will be arranged along. In such an arrangement, the primary particles 100b that are not in contact with the conductive material 201 exist far away from the chain-shaped conductive material 201 serving as a conductive path. For this reason, electrons move along a long path, and the resistance value increases. That is, when a large current is passed, the loss increases and it becomes difficult to increase the output.

  In view of such problems, when forming a slurry-like electrode material, mixing and stirring while shearing the material using a planetary stirring mixer, called a high-speed disper, equipped with a blade that rotates at high speed (disper) In some cases, the electrode material is manufactured. Accordingly, the secondary particles 101 of the positive electrode active material are subdivided into primary particles 100 by a strong shearing force. However, stirring while shearing causes the chain-shaped conductive material 201 to be subdivided as shown in FIG. 3D, and the conductive path between the primary particles 100 of the active material and the current collector is broken. . That is, the conductive path itself is not formed, and as a result, the resistance value of the electrode is increased.

  Accordingly, an object of the present invention is to provide an electrode manufacturing method for achieving high output of a nonaqueous electrolyte storage element.

In order to achieve the above object, the present invention provides a method for producing a sheet-like electrode constituting a nonaqueous electrolyte storage element,
An active material stirring step in which a mixture of an electrode active material and a binder having a primary particle size of 1 μm or less is stirred to form a pasty active material by shearing with a planetary stirring mixer with a disper ;
A conductive material stirring step of forming a paste-like conductive material by stirring a mixture of a conductive material having a primary particle size of 1 μm or less and a binder with a planetary stirring mixer without a disper ;
An electrode material mixing step of stirring the mixture of the paste active material and the paste conductive material to form a paste electrode material;
Applying the paste-like electrode material onto a sheet-like current collector;
It is set as the electrode manufacturing method of the nonaqueous electrolyte storage element characterized by including this.

The electrode manufacturing method is suitable when the electrode is a positive electrode. If the positive electrode active material is LiFePO ₄ , the material is inexpensive and stable supply is expected. Can be expected to provide.

  According to the electrode manufacturing method for a nonaqueous electrolyte storage element of the present invention, high output of the nonaqueous electrolyte storage element can be expected.

It is a figure which shows the external appearance of a non-aqueous electrolyte electrical storage element. It is sectional drawing of the said nonelectrolyte electrical storage element. It is a figure for demonstrating the problem of the conventional nonelectrolyte electrical storage element. It is a figure which shows the manufacturing process of the electrode material used for the nonelectrolyte electrical storage element which concerns on the Example of this invention. It is a figure for demonstrating the effect of this invention.

=== Structure of Nonaqueous Electrolyte Storage Element ===
As an example of the present invention, a nonaqueous electrolyte storage element including an electrode manufactured by the method of the present invention is given. As a specific embodiment thereof, for example, a form similar to that of the conventional nonaqueous electrolyte storage element 1 shown in FIG. 1 can be adopted. However, in the present embodiment, the positive electrode side sheet-like electrode 10 is manufactured by a method different from the conventional method, thereby achieving high output of the non-aqueous electrolyte storage element 1. Hereinafter, a specific configuration of the nonaqueous electrolyte storage element in the present embodiment will be described.

=== About Positive Electrode Active Material ===
In this embodiment, the positive electrode is manufactured by a method different from the conventional method. As the positive electrode active material, lithium nickelate (LiNiO ₂ ), lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ) and the like are well known, but at present, safer than LiNiO ₂ , LiCoO ₂ is often used because it has better capacity characteristics than LiMn ₂ O ₄ .

However, in this example, lithium iron phosphate (LiFePO ₄ ) is used instead of the above-described general positive electrode active material. This LiFePO ₄ does not contain expensive cobalt like LiCoO ₂ , but contains iron that is inexpensive and is expected to be stably supplied. In addition, safety is high. Considering current environmental problems and future depletion of fossil fuels, it is indispensable to stably mass-produce non-aqueous electrolyte storage elements, and the significance of adopting this LiFePO ₄ as a positive electrode active material is therefore also large.

While LiFePO ₄ has the advantages described above, it has a disadvantage that its conductivity is lower than that of other positive electrode active materials. Therefore, the demand for fine particles for LiFePO ₄ is greater than that for other positive electrode active materials. And if the problem regarding microparticulation is solved in this LiFePO ₄ , the solution can be applied to other positive electrode active materials. From this point of view, this LiFePO ₄ was selected as the positive electrode active material of the non-aqueous electrolyte storage element according to the example of the present invention.

=== Production Method of Positive Electrode Active Material ===
First, prior to manufacturing the sheet-like positive electrode, the positive electrode active material itself is manufactured. In this example, a positive electrode active material was produced by the following procedures (A) to (E).

(A) Iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and lithium carbonate (Li ₂ CO ₃ ) are in a predetermined molar ratio. Mix like so.
(B) The mixture obtained in (A) is mixed while pulverizing for 10 hours with a ball mill using 2-propanol as a solvent.
(C) The mixture pulverized and mixed in (B) is vacuum-dried to remove the solvent to obtain a precursor.
(D) The precursor is placed in an alumina casserole and calcined in an annular firing furnace at 300 ° C. for 5 hours while flowing argon at 0.5 L / min.
(E) The precursor calcined by (D) is calcined at 650 ° C. for 20 hours while flowing argon at 0.5 L / min to synthesize LiFePO ₄ powder (hereinafter, positive electrode active material).

=== Production Method of Positive Electrode ===
The sheet-like positive electrode in this example was adjusted such that the weight ratio of the positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride as a binder (binder) was 90: 5: 5. A positive electrode material is applied to a sheet-like current collector. The present embodiment is characterized in the process of manufacturing this positive electrode material.

  FIG. 4 shows the procedure for preparing the positive electrode material. First, the positive electrode active material and the binder were mixed at a weight ratio of 90: 4.5 (s1 to s3), N methylpyrrolidone as a solvent was added to the mixture, and the mixture was stirred for 30 minutes using a planetary mixer with a disperser. (S4). Thus, about a positive electrode active material, it stirs, shearing with a binder, and produces | generates a slurry-like positive electrode active material (s5).

  On the other hand, the conductive material and the binder are mixed at a weight ratio of 5: 0.5 (s11 to d13), N methylpyrrolidone is added to the mixture, and the mixture is stirred with a planetary mixer (s14). That is, the conductive material is agitated with the binder without shearing to produce a slurry-like conductive material (s15). Then, the slurry-like positive electrode active material and the conductive material are mixed (s6), and mixed with a planetary stirring mixer for 10 minutes to obtain a slurry-like positive electrode material (s7, s8).

  The slurry-like positive electrode material thus prepared is applied onto the aluminum foil 12 which is a positive electrode sheet-like current collector and dried. Then, when the coated surface is rolled by a rolling roller and the tab 40 is attached to the current collector 12, the sheet-like positive electrode 10 is completed (see FIG. 2).

=== Method for Producing Negative Electrode ===
The negative electrode of the nonaqueous electrolyte storage element of this example is manufactured in the same manner as the conventional nonaqueous electrolyte storage element. Specifically, a solvent (N-methylpyrrolidone) was added to a mixture of graphite and a binder (polyvinylidene fluoride) as a negative electrode active material to obtain a slurry-like negative electrode material. The weight ratio of graphite, binder and solvent was 95: 3: 2.
The slurry-like negative electrode material thus prepared is applied onto the copper foil 22 which is a negative electrode sheet-like current collector and dried. Then, when the coated surface is rolled using a rolling roller and the current collecting tab 40 is attached, the sheet-like negative electrode 20 is completed (see FIG. 2).

=== Assembly ===
Next, a process of assembling the non-electrolyte storage element 1 shown in FIGS. 1 and 2 using the sheet-like positive electrode 10 and the sheet-like negative electrode 20 prepared by the above-described procedure will be described. First, the sheet-like positive electrode 10 and the sheet-like negative electrode 20 are arranged to face each other with a separator 50 interposed therebetween to produce one unit laminate 60a, and the electrode laminate 60 obtained by laminating a predetermined number of the laminates 60a in a vacuum. And dried at 105 ° C. for 20 hours.

  And after connecting each tab 40 attached to the sheet-like collector (12, 22) with positive electrodes and negative electrodes, the electrode laminated body 60 is made into thickness 0 in the glow box in argon atmosphere. .Into the bag of the outer package 30 made of 11 mm aluminum laminate film. At this time, the tab 40 is led out of the exterior body 30. And after inject | pouring electrolyte solution in the exterior body 30, a laminate film is thermocompression-bonded and sealed, and the nonelectrolyte electrical storage element 1 finally shown in FIG.1 and FIG.2 is completed. The electrolytic solution was prepared by further adding vinylene carbonate to a solution obtained by dissolving 1 mol / L LiPF6 in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7.

=== Characteristic evaluation ===
The capacity characteristics of the non-aqueous electrolyte storage element (invention product) and the conventional non-aqueous electrolyte storage element (conventional product) in the above examples were compared. The product of the invention and the conventional product differ only in the production method of the positive electrode material, and the production method of the negative electrode and the subsequent assembly procedure are the same as those of the above-described invention product. Here, the following two types of conventional products (conventional product 1 and conventional product 2) having different positive electrode material manufacturing methods were produced and compared with the inventive product.

<Positive electrode material of conventional product 1>
The positive electrode active material (LiFePO ₄ ), the conductive material (acetylene black), and the binder (polyvinylidene fluoride) were weighed so as to have a predetermined weight ratio, and then a solvent (N methylpyrrolidone) was added to the mixture and mixed with a planetary stirring mixer. A positive electrode material of conventional product 1 was prepared by mixing with stirring for a minute. That is, the mixture of all the elements contained in the positive electrode material was stirred without shearing. The weight ratio of the positive electrode active material, the conductive material, and the binder was 90: 5: 5.

<Conventional product 2>
A mixture of a positive electrode active material, a conductive material, a binder, and a solvent was mixed with the conventional product 1 while stirring with a planetary stirring mixer with a disperser for 30 minutes to produce a positive electrode material. That is, all elements included in the positive electrode material were stirred so as to shear.

<Capacitance characteristics>
The non-aqueous electrolyte storage element of the above invention product, the conventional product 1 and the conventional product 2 is subjected to constant current charging at a temperature of 25 ° C. at a charging rate of 0.2 C until the voltage reaches 4.0 V. After that, constant current discharge was performed at various discharge rates until the final voltage became 2.0 V, and the charge / discharge capacity of each power storage element was measured.

The measurement results are shown in Table 1 below.

  In Table 1, the capacity of each power storage element is shown as a relative value when the theoretical capacity obtained from the filling amount of positive and negative active materials is 100. In addition, the relative capacity of the conventional product when the capacity of the invention product is set to 100 when the discharge is performed under the same conditions is shown in parentheses.

  From the results shown in Table 1, the nonaqueous electrolyte storage element according to the invention has a high capacity at all discharge rates, that is, whether it is discharged with a small current or a large current. I was able to. Looking at the relative capacity of the conventional product shown in parentheses in the table with the invention, the effect of increasing the capacity at the time of large current discharge with a high discharge rate is remarkable. That is, it was confirmed that high output was achieved. This is because the slurry-like positive electrode active material and the slurry-like conductive material were individually prepared, and the positive electrode active material was agitated while being sheared. As shown in FIG. The mixed positive electrode active material 100 and the conductive material 201 that maintains the chain shape are mixed so that each primary particle 100 of the positive electrode active material contacts the chain-shaped conductive material 201 that maintains the function as a conductive path. This is thought to be due to the structure.

=== Application to negative electrode ===
In the said Example, the manufacturing method of this invention was applied only to the positive electrode. Needless to say, the present invention extends to a method for producing a negative electrode, and can be applied to a case where a negative electrode material is produced by mixing a nanoparticulated negative electrode active material with a conductive material in a slurry state. In addition, it is conceivable to produce a negative electrode material by slurrying a mixture of nanoparticulate graphite and graphite in which secondary particles are chain-like, as in the case of a conventional negative electrode. It is possible to apply the electrode manufacturing method.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte storage element 10 Positive electrode 11 Positive electrode material 12 Positive electrode side sheet-like current collector 20 Negative electrode 21 Negative electrode material 22 Negative electrode side sheet-like current collector 30 Exterior body 40 Tab 50 Separator 100 Primary particle of positive electrode active material 101 Positive electrode active Secondary particles of material 200 Primary particles of negative electrode active material 201 Secondary particles of negative electrode active material

Claims (3)

A method for producing a sheet-like electrode constituting a nonaqueous electrolyte storage element,
An active material stirring step in which a mixture of an electrode active material and a binder having a primary particle size of 1 μm or less is stirred to form a pasty active material by shearing with a planetary stirring mixer with a disper ;
A conductive material stirring step of forming a paste-like conductive material by stirring a mixture of a conductive material having a primary particle size of 1 μm or less and a binder with a planetary stirring mixer without a disper ;
An electrode material mixing step of stirring the mixture of the paste active material and the paste conductive material to form a paste electrode material;
Applying the paste-like electrode material onto a sheet-like current collector;
The electrode manufacturing method of the nonaqueous electrolyte electrical storage element characterized by including this.   The method for producing an electrode for a non-aqueous electrolyte storage element according to claim 1, wherein the electrode is a positive electrode. The method for manufacturing an electrode of a nonaqueous electrolyte storage element according to claim 2, wherein the positive electrode active material is LiFePO ₄ .

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