JP4016630B2 - Method for manufacturing lithium ion battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery manufacturing method.
[0002]
[Prior art]
Until now, many kinds of chemical batteries such as dry batteries, alkaline batteries, lead storage batteries, nickel cadmium batteries, nickel metal hydride batteries, lithium primary batteries, lithium secondary batteries have been put into practical use. Of these, most of lead acid batteries, nickel cadmium batteries, nickel metal hydride batteries, lithium primary batteries, and lithium secondary batteries are constructed by laminating or winding a positive electrode and a negative electrode. A separator for holding the liquid is provided.
[0003]
Conventional separators include non-woven fabrics, glass mats, porous films, etc., to suit the battery system and battery structure, and are assembled together with the positive and negative electrodes during electrode lamination and winding, respectively. It is configured.
[0004]
Further, as such a porous separator, there is also known one in which spherical resin particles are bonded together and a gap for holding an electrolyte solution is provided between the spherical particles (Japanese Patent Laid-Open No. 1-167948).
[0005]
Also, in lithium-ion batteries, the separator and electrode are not separate, but the assembly of the electrode group is improved by forming a porous resin layer integrally on at least one side of the electrode to form a separator. This is also known (Japanese Patent Laid-Open No. 11-345606).
[0006]
In a polymer lithium ion battery, as a method for producing a similar porous resin layer in an electrode, a material obtained by dissolving polyvinylidene fluoride (PVDF) resin in N-methylpyrrolidone (NMP) is used as a binder. Further, a technique for forming a porous phase of PVDF by adding another solvent insoluble in PVDF after coating, for example, water to extract NMP is also reported.
[0007]
[Problems to be solved by the invention]
The method of providing a porous resin layer integrally on the electrode to form a separator is that the separator is already integrated on the electrode, so the electrode group is assembled in a two-part configuration of the positive electrode and the negative electrode. Compared with what is assembled by the three-part structure of a positive electrode, a negative electrode, and a separator, assemblability improves in each step.
[0008]
However, from the viewpoint of battery performance and quality, the physical properties, shape, and structure of the resin layer are important factors, and a manufacturing method for forming the resin layer that can control these factors is required. The present invention has been made in view of the above-described circumstances, and is a method of integrating a porous resin layer on an electrode, and provides a manufacturing method advantageous for controlling the physical properties, shape, and structure of the porous resin layer. The purpose is to do.
[0009]
[Means for Solving the Problems]
A lithium ion battery according to the present invention is a lithium ion battery having a porous resin layer composed of butyl isocyanate fine particles between a positive electrode, a negative electrode, and both positive and negative electrodes, and is integrated with an electrode on at least one of the positive and negative electrodes The porous resin layer is provided.
[0010]
The present invention is a manufacturing method of the lithium-ion battery, after forming a mixture comprising a diazo organic compound fine particles to decompose by heating with butyl isocyanate to be porous resin layer on at least one of the electrodes of the positive and negative electrodes, A porous resin layer integrated with an electrode is provided by decomposing a diazo organic compound in butyl isocyanate by predetermined heating.
[0012]
Specifically, using a suspension liquid of butyl isocyanate are dispersed diazo organic compound fine particles to the resin solution dissolved in a solvent, which was coated on the electrode, is more foamed pressure heat porous and dried This is a production method for obtaining a resin layer.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the battery according to the production method of the present invention, the porous resin layer is formed in an integrated form on the electrode, and this resin layer is used as a separator. The resin layer may be formed on any of the positive and negative electrodes, as long as the original function as a separator, ie, the prevention of contact between the positive electrode and the negative electrode and the retention function of the electrolyte, is secured. You may form in.
[0015]
The thickness of the porous resin layer may be any as long as it ensures the original function as a separator, at least between positive and negative electrodes, preventing contact between the positive electrode and the negative electrode and retaining the electrolyte. When the battery system is a lithium battery system such as a lithium ion battery or a lithium primary battery, the thickness of the resin layer functioning as a separator is suitably around 10 μm to 60 μm, and the battery system is a nickel cadmium battery, a nickel hydrogen battery, or the like In the case of the alkaline storage battery system, the thickness is suitably around 0.1 mm to 0.8 mm, and in the case where the battery system is a lead storage battery, the thickness is suitably around 0.5 mm to 1.2 mm. However, it is not limited to this.
[0016]
The thickness of the resin layer depends on the thickness of the coating film when the resin layer is formed on the electrode by coating or the like, and can be easily adjusted by the viscosity of the coating solution and the coating method employed.
[0017]
The porosity of the porous resin may be any as long as it can hold an electrolytic solution sufficient to cause the target electrode reaction to be sufficiently performed and can obtain the target electrode reaction rate in any battery system. However, the hole shape, hole size, and number of holes have a range to be adapted depending on the battery system. If the production method of the present invention is used, the purpose is to control the type of foaming agent, the particle size of the foaming agent fine particles, the concentration of the foaming agent fine particles, the viscosity of the coating film during foaming, the temperature rise in the foaming process, the temperature drop rate, A porous resin layer having a pore shape, a pore size, and a number of pores can be easily obtained. For example, if you want to make many small pores, increase the particle size of the foam fine particles, increase the resin concentration, increase the foam material concentration, and foaming will occur at the same time, so that the drying proceeds quickly. You can devise the speed.
[0018]
Moreover, as a method for forming a coating film of the resin layer on the electrode, a coating method such as a doctor blade, a die head coater, or spraying can be used. In the case of a lithium battery system in which the resin layer is designed to be relatively thin, accuracy is required, and therefore it is preferable to use a doctor blade or a die head coater. Here, since the required accuracy is slightly relaxed in the alkaline storage battery system, a spray spraying method can also be adopted. Furthermore, a lead storage battery having a thick resin layer can employ a dip method in which an electrode is immersed in a resin solution and pulled up. However, it is not limited to this.
[0019]
As the resin constituting the porous resin layer, it is assumed that a resin that does not dissolve in the electrolyte solution is selected in the lithium battery system, and butyl isocyanate, which is a urea resin , can be selected .
[0020]
As the foaming agent, those organic materials systems such as di-azo compounds are useful.
[0021]
【Example】
Examples of the present invention will be described below.
[0022]
The case where the manufacturing method of the present invention is applied to a lithium ion battery will be described.
[0023]
FIG. 1 is a cross-sectional view of a cylindrical battery used in this example, and FIG. 1B is an enlarged view of the electrode plate group portion of the cylindrical battery cross-sectional view (a). As shown in FIG. 1 (b), the electrode group consists of a positive electrode active material layer 1 in which a conductive material carbon powder and a binder PVDF are mixed with an active material LiCoO ₂ powder. ) A positive electrode provided on both surfaces of the foil 2, and a negative electrode provided with negative electrode active material layers 3 mixed with active material graphite powder and binder PVDF on both surfaces of the negative electrode current collector copper (Cu) foil 4. A porous resin layer 5 that functions as a separator provided on the negative electrode by the production method of the present invention is provided between the positive and negative electrodes.
[0024]
As shown in FIG. 1 (a), after the wound electrode plate group is loaded into the battery case 10, the positive electrode lead 7 and the negative electrode lead 8 taken out from the electrode plate group are connected to the sealing plate 9 and the battery, respectively. The case 10 is resistance welded to the lower part of the case 10, and an organic electrolyte _{6 in} which 1 mol / liter of LiPF ₆ is dissolved is injected into a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1, and sealed. The battery contents are hermetically sealed by keeping the electrical insulation between the plate 9 and the battery case 10, and the positive case opening edge is bent inward and crimped via a polypropylene gasket 11. It is.
[0025]
Thereafter, the battery performance was evaluated using this battery.
[0026]
The subject of the present invention is a method for producing a porous resin layer as described above. In this example, PVDF is used as a porous resin component, and calcium carbonate (CaCO ₃ ) is combined as a foaming material ( Reference Example 1). An example (Example 1 ) in which a butyl isocyanate resin is used as the porous resin component and a diazo organic compound is combined as the foaming material will be described.
[0027]
( Reference Example 1)
In Reference Example 1, a negative electrode active material layer in which graphite powder of an active material and PVDF of a binder are mixed is used as a substrate for forming a porous resin layer on a negative electrode sheet provided on both surfaces of a Cu foil of a negative electrode current collector. Using.
[0028]
First, 200 g of a solution in which 12% by mass of PVDF as a porous resin component is dissolved in NMP is prepared, and 10 g of CaCO ₃ fine powder (particle size: 1 μm to 5 μm) as a foaming material is added thereto and kneaded sufficiently. The surface of the negative electrode was uniformly applied using a die head coater so that the coating thickness was 30 μm.
[0029]
Next, this electrode plate is put into a dryer heated to 160 ° C., and CaCO ₃ is decomposed (CO ₂ generation) by heating to promote foaming in the coating film, and NMP is evaporated to dry the coating film. A porous resin layer comprising: The thickness of the porous resin layer after drying was about 25 μm, and it was found that the porosity was about 30% from the relationship between the coating film mass and the volume. With this formulation, an electrode having a porous resin layer provided on both sides of the negative electrode was produced, and a positive electrode using LiCoO ₂ as an active material was wound to produce a cylindrical battery (battery A) having the above-described configuration.
[0030]
(Example 1 )
Also in Example 1 , a negative electrode active material layer obtained by mixing active material graphite powder and binder PVDF was used as a substrate for forming a porous resin layer on a negative electrode sheet provided on both sides of a Cu foil of a current collector. It was.
[0031]
First, 200 g of a solution in which 50% by mass of a butyl isocyanate resin as a porous resin component was dissolved in toluene was prepared, and 5 g of a diazo organic compound (particle size: 0.2 μm to 2.0 μm) as a foaming material was added thereto. Was sufficiently kneaded and then uniformly applied to the surface of the negative electrode using a die head coater so that the coating thickness was 30 μm.
[0032]
Next, this electrode plate is placed in a dryer heated to 130 ° C., and the diazo organic compound is decomposed (N ₂ generation) by heating to promote foaming in the coating film, and toluene is evaporated to dry the coating film. Then, a porous resin layer made of butyl isocyanate was prepared. The thickness of the porous resin layer after drying was about 20 μm, and the porosity was about 50%. With this formulation, an electrode provided with a porous resin layer on both sides of the negative electrode was prepared, and a positive electrode using LiCoO ₂ as an active material was wound to prepare a cylindrical battery (battery B) having the above-described configuration.
[0033]
In order to confirm the form of the porous resin layer produced in Reference Example 1 and Example 1 , the negative electrode provided with the porous resin layer was cut and the cross section was observed with a microscope. As a result, as shown in the schematic diagram of FIG. 2, it was found that a coating film in which three-dimensional continuous holes were uniformly distributed over the entire resin layer was obtained.
[0034]
(Comparative example)
For comparison with the battery according to the present invention having a structure in which the porous resin layer produced by the above-described formulation of the present invention is integrated with an electrode, a separate separator made of a polypropylene porous resin film is used as a positive and negative electrode. A battery (battery C) having a conventional structure wound between them was produced. This separator is a commercially available porous resin film having a thickness of 25 μm and a porosity of 33%.
[0035]
Here, it was also clarified that the battery according to the manufacturing method of the present invention has a significant advantage in the assembly property of the electrode group, as compared with the battery having a conventional configuration in which the separator is separated.
[0036]
Next, tests on the performance of the batteries according to the above-described Examples , Reference Examples, and Comparative Examples were performed.
[0037]
It should be noted that both the battery A and the battery B according to the reference example and the example in which the negative electrode and the separator are integrated, and the battery C according to the comparative example in which the electrode and the separator are separated from each other, have positive and negative electrodes of the same size. The battery used was the same battery size and shape.
[0038]
Each battery was first charged and discharged for 3 cycles at a constant current of 1 / 5C (end-of-charge voltage of 4.1 V, end-of-discharge voltage of 3.0 V), and then the discharge load characteristics were determined by setting the discharge to 1 C and 2 C.
[0039]
The result is shown in FIG. FIG. 3 shows the capacities at the time of 1 / 5C, 1C, and 2C discharges. In the 1 / 5C discharge, all the batteries show almost the same capacity.
[0040]
However, it was found that with high rate discharges of 1C and 2C, the battery A shows equivalent load characteristics and the battery B shows good load characteristics compared to the battery C using a conventional separator.
[0041]
The reason why the battery B is excellent seems to be related to the fact that the porosity of the separator was relatively high (the porosity of the battery B was 50%).
[0042]
In the case of a conventional separator, in general, when the porosity is increased, the strength of the film itself is reduced, and inconveniences such as breakage occur when wound separately, so it is actually difficult to increase the porosity.
[0043]
However, the porous resin layer according to the production method of the present invention integrated with the electrode is held in the electrode even if the porosity is increased, so that there is no problem in strength and the advantage that the porosity can be increased. I found out that In other words, the production method of the present invention is a very convenient technique for increasing the output of a lithium ion battery.
[0044]
Further, as a result of intensive studies, it has been found that if the production method of the present invention is used, the porosity can be further increased and the diameter and the number of holes can be controlled .
[0045]
In this embodiment, a cylindrical lithium ion battery has been described as an example. However, the technology of the present invention can be applied even when the battery shape is a button type battery, a coin type battery, or a square type battery. Further, in this embodiment, the battery structure in which the electrodes are wound is used, but the present invention may be applied to a battery structure in which flat positive and negative electrodes are stacked.
[0046]
Furthermore, in this embodiment, the lithium ion battery has been described as an example. However, the manufacturing method of the present invention can be applied to many of lead storage batteries, nickel cadmium batteries, nickel metal hydride batteries, lithium primary batteries, and other lithium secondary batteries. is there.
[0047]
In any battery system, when the production method of the present invention is used, the battery assembly process can be facilitated, the pore diameter, the number of holes, etc. can be easily achieved compared to the conventional battery using a separate separator. It is possible to improve the performance of the battery because it can control the battery, and further, since the resin layer covers the active material layer of the electrode, it is possible to suppress the falling off of the active material layer, so that the durability can be improved. .
[0048]
【The invention's effect】
According to the present invention, a method for providing a porous resin layer on an electrode can provide a production method advantageous for controlling the physical properties, shape, and structure of the porous resin layer.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a test battery and electrode group in an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a porous resin layer in an embodiment of the present invention. Characteristics [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Positive electrode collector 3 Negative electrode active material layer 4 Negative electrode collector 5 Porous resin layer 6 Electrolytic solution 7 Positive electrode lead 8 Negative electrode lead 9 Sealing plate 10 Battery case 11 Gasket

Claims (2)

A method for producing a lithium ion battery having a porous resin layer made of butyl isocyanate between a positive electrode, a negative electrode, and both positive and negative electrodes, and a mixture of butyl isocyanate and diazo organic compound fine particles on at least one of the positive and negative electrodes after formation, the method for producing a lithium ion battery and providing a porous resin layer integrated by decomposing diazo organic compounds in butyl isocyanate and the electrode by heating. 2. The method for producing a lithium ion battery according to claim 1, wherein a particle diameter of the diazo organic compound fine particles is 0.2 μm to 2.0 μm.

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