JP2011008965A - Manufacturing method for positive electrode of lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology concerning to a manufacturing method for a positive electrode of a lithium ion secondary battery and a lithium ion secondary battery, which can restrain increase of internal resistance at a neglected condition after shipping.SOLUTION: In the manufacturing method for the positive electrode of the lithium ion secondary battery having a paste preparation process 10 of preparing positive electrode active material paste formed by mixing electrode materials of the positive electrode, the paste preparation process 10 includes a drying process 13a of removing moisture remained in a pore made of cellulosic polymer by drying cellulosic polymer at a powder state, a dissolving process 13b of creating a thickener by dissolving the cellulosic polymer dried in the drying process 13a into water, and a process 13c of mixing the thickener created in the dissolving process 13b and the electrode material.

Description

  The present invention relates to a method for manufacturing a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery technology capable of suppressing an increase in internal resistance in a state of being left for a long period after shipment.

  In recent years, in the field of automobiles, the development of electric vehicles and hybrid vehicles has been promoted while environmental issues and resource issues have been screamed. As a power source for these electric vehicles and hybrid vehicles, high operating voltage and high energy density have been developed. The lithium ion secondary battery which has has attracted much attention, and in particular, the demand for 4V class large lithium ion secondary batteries is widespread.

The positive electrode for a lithium ion secondary battery, as the operating voltage of 4V class is obtained, LiCoO _2, LiNiO ₂ of layered rock salt structure, LiMn ₂ O ₄ of spinel structure, and a part of them to other elements A positive electrode active material made of a substituted lithium transition metal composite oxide (lithium-containing composite oxide) or the like is often used. Among these composite oxides, a lithium ion secondary battery using a LiCoO ₂ -based lithium-containing composite oxide as a positive electrode active material is presently used because of its high operating voltage and high energy density. Occupies the mainstream.

  Then, a positive electrode active material prepared in a paste form is prepared by stirring and mixing an electrode material having such a positive electrode active material, a binder, a thickener, and a conductive material added as necessary. A positive electrode is formed by generating a material paste, applying the positive electrode active material paste to a sheet-like current collector made of an aluminum foil, drying, pressing, and cutting into a sheet.

By the way, it is known that a lithium ion secondary battery that has already been completed and shipped, when it is left for a long time after charging, gradually increases its internal resistance and deteriorates battery performance.
That is, FIG. 4 shows the degree of increase in internal resistance with respect to the standing time after charging in a conventional lithium ion secondary battery according to the state of charge (SOC: State Of Charge) (the state of charge in this figure). The relationship between A%, B%, and C% is A%>B%> C%.) As shown in this figure, the lithium ion secondary battery is charged. It is known that the internal resistance of the lithium ion secondary battery gradually increases as the standing time increases, although there is a difference depending on the remaining capacity of electricity, that is, the state of charge (SOC) of the lithium ion secondary battery. ing.
This phenomenon is thought to be due to the following factors.

In order to achieve a 4V class operating voltage, the electrolyte must be a non-aqueous electrolyte. Moreover, LiPF ₆ which is a halogen compound is often used as the electrolyte in the non-aqueous electrolyte. However, if a lithium ion secondary battery that has already been completed and shipped is left to stand for a long time after charging, some moisture is inevitably mixed in the electrolyte solution that should be non-aqueous, or moisture is contained in other electrode materials. For example, the reaction shown in the following formula (1) occurs to generate hydrogen fluoride HF.

LiPF ₆ + H ₂ O → 2HF + LiF + POF ₃ (1)

  Hydrofluoric acid, which is an aqueous solution of generated hydrogen fluoride, has a problem of deteriorating material constituting the battery and further degrading battery performance. That is, as a result of the deterioration of the constituent material, the internal resistance is deteriorated (increased).

For this reason, when manufacturing a 4V-class large-sized lithium ion secondary battery, it has been devised to remove moisture inside the battery as much as possible. However, it is still difficult to completely remove moisture from the inside of the battery, resulting in deterioration of battery performance (increase in internal resistance) considered to be caused by residual moisture.
Although the deterioration of the battery performance related to such a lithium ion battery is insignificant to the extent that it does not become a problem in daily use, it is required to maintain the performance over a long period of more than 10 years. In some applications, the size may not be negligible.

  Therefore, the present inventor has paid attention to the presence of carboxymethyl cellulose (CMC) contained in the positive electrode active material paste as one factor that causes moisture to be mixed into the battery with respect to an increase in the internal resistance of the lithium ion secondary battery.

  That is, FIG. 5 shows the degree of increase in internal resistance with respect to the standing time after charging in a conventional lithium ion secondary battery according to CMC content (aWt%, bWt%, cWt indicating the content of CMC in this figure). % Is a relationship diagram of aWt%> bWt%> cWt%.) As shown in this figure, a lithium ion secondary having an organic solvent to which CMC is not added as a positive electrode. When the increase in internal resistance with respect to the standing time of lithium ion secondary batteries including batteries, each of which has a different CMC content contained in the positive electrode active material paste, was examined, the higher the CMC content, the higher the internal resistance. It turns out that the degree becomes large.

  For this reason, the present inventor pays attention to the moisture remaining in the pores of the CMC as one of the factors causing the increase in the internal resistance of the lithium ion secondary battery, and effectively reduces the moisture as much as possible. Therefore, trial and error were repeated in order to minimize the deterioration of lithium ion secondary battery performance (increase in internal resistance).

  On the other hand, in the method for producing a positive electrode for a lithium ion secondary battery, various techniques can be used for drying the CMC contained in the positive electrode active material paste, as shown in "Patent Document 1" to "Patent Document 3". It is shown.

JP 2006-236886 A JP 2007-234277 A International Publication No. 2006/061940

In the above-mentioned “Patent Document 1”, it is obtained after obtaining a lithium-containing composite oxide in a powder state in order to obtain a lithium-ion-containing composite oxide coated with a fired product of CMC in the manufacturing process of the positive electrode active material. Further, a technique is disclosed in which 0.1% of CMC in a powder state is added to 100 parts by mass of the oxide, dry mixing is performed, and then the obtained powder is fired at 250 ° C.
However, even if the powder containing other components (lithium-containing composite oxide) is dried at 250 ° C., not all of the added heat can be added to the powdered CMC, and the powder is contained in the pores of the CMC. It is difficult to effectively remove residual moisture.

In the above-mentioned “Patent Document 2”, in the manufacturing process of the positive electrode active material, 50 parts by weight of CMC aqueous solution is added to 100 parts by weight of lithium ion-containing composite oxide in a powder state, and a double-arm kneader is used. A technique is disclosed in which a mixture obtained by stirring and drying into a paste is dried by a hot air drier, and secondary particle powder of a positive electrode active material is obtained by a grinding pulverizer.
However, even if the mixture already in paste form is dried, even if the solvent (pure water) contained in the CMC aqueous solution can be completely vaporized and removed, the moisture remaining in the pores of the CMC It is difficult to remove effectively.

In the above-mentioned “Patent Document 3”, although it relates to a process for producing a negative electrode active material, a negative electrode active material, a binder, and a thickener made of CMC are added to form a negative electrode mixture paste (negative electrode). An active material paste) is prepared, the negative electrode mixture paste is applied to a metal foil of a current collector, dried, rolled, and then heat-treated within a range of 140 ° C. to 150 ° C. is disclosed. In addition, it is described that a thickener made of CMC can also be used for the positive electrode active material paste.
However, similarly to the above-mentioned “Patent Document 2”, even if the mixture already in a paste form is dried, the solvent (pure water) contained in the CMC aqueous solution can be completely vaporized and removed. It is difficult to effectively remove water remaining in the pores of CMC.

  In view of such a point, the present invention relates to a method for manufacturing a positive electrode for a lithium ion secondary battery capable of suppressing an increase in internal resistance in a state of being left for a long time after shipment, and a lithium ion secondary battery. The issue is to provide technology.

  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, it is a manufacturing method of the positive electrode for lithium ion secondary batteries which has the paste preparation process which prepares the positive electrode active material paste comprised by mixing the electrode material of a positive electrode, Comprising: The said paste preparation process includes Drying the cellulosic polymer in a powder state to remove water remaining in the pores of the cellulosic polymer, and dissolving the cellulosic polymer dried in the drying step in water And a step of mixing the thickening material generated in the melting step and the electrode material.

  In Claim 2, it is a manufacturing method of the positive electrode for lithium ion secondary batteries shown in Claim 1, Comprising: The drying temperature in the said drying process shall be 265 degreeC or more and 275 degrees C or less.

  In Claim 3, it is a manufacturing method of the positive electrode for lithium ion secondary batteries shown in Claim 1 or Claim 2, Comprising: The said cellulose polymer is carboxymethylcellulose.

  In Claim 4, It is a lithium ion secondary battery provided with the positive electrode comprised using the positive electrode active material paste prepared by mixing the electrode material for positive electrodes, Comprising: The said positive electrode active material paste is a pore inside. Cellulosic polymer from which moisture remaining in is removed by drying is included as a thickener.

  In Claim 5, it is a lithium ion secondary battery shown in Claim 4, Comprising: The drying temperature of the said cellulosic polymer shall be 265 degreeC or more and 275 degrees C or less.

  In Claim 6, it is a lithium ion secondary battery shown in Claim 4 or Claim 5, Comprising: The said cellulose polymer is carboxymethylcellulose.

As effects of the present invention, the following effects can be obtained.
That is, it is possible to provide a method for manufacturing a positive electrode for a lithium ion secondary battery that can suppress an increase in internal resistance in a state of being left for a long time after shipment, and a technique related to the lithium ion secondary battery.

The block diagram which showed the flow of the manufacturing process of the positive electrode for lithium ion secondary batteries based on one Example of this invention. Similarly, the diagram which showed the relationship between drying temperature and the water | moisture content contained in powdery CMC. The block diagram which showed the flow of the manufacturing process of the conventional positive electrode for lithium ion secondary batteries. In the conventional lithium ion secondary battery, the relationship figure which showed the raise degree of internal resistance with respect to leaving time according to the ratio of the charge condition. The related figure which showed the raise degree of the internal resistance with respect to leaving time in the conventional lithium ion secondary battery according to content of CMC.

  Next, embodiments of the invention will be described.

[Lithium ion secondary battery]
First, the whole structure of the lithium ion secondary battery which comprises the positive electrode for lithium ion secondary batteries manufactured by the manufacturing method of this invention is demonstrated.
The lithium ion secondary battery is configured as, for example, a cylindrical battery or a square battery configured by accommodating an electrode body including a sheet-like positive electrode and a negative electrode in a battery case in a wound state.
Specifically, the lithium ion secondary battery comprises an electrode body formed by laminating a positive electrode and a negative electrode formed in a sheet shape with a separator interposed therebetween, and further the electrolysis is performed in a state where the electrode body is wound. It is comprised by accommodating in the battery case filled with the liquid.
The lithium ion secondary battery configured as described above includes an electrode body that includes a positive electrode, a negative electrode, and a separator, and a battery case that holds the electrode body, and the electrolyte solution is non-aqueous. An electrolyte is used.

  The sheet-shaped positive electrode (positive electrode sheet-like electrode) is made by mixing a positive electrode active material capable of inserting and extracting lithium ions with an electrode material such as a conductive material, a binder, and a thickener. The coating step of applying the positive electrode active material paste prepared in the above to the surface of a sheet-like current collector made of aluminum foil or the like, the drying step of drying the current collector coated with the positive electrode active material paste, and the drying step The positive electrode active material paste is manufactured through a pressing process that presses the dried current collector to increase the density of the positive electrode active material.

  As the positive electrode active material, a known positive electrode active material such as a lithium transition metal composite oxide can be used as described above. Lithium transition metal composite oxide is a preferred material for the positive electrode active material because of its low electrical resistance, excellent lithium ion diffusion performance, high charge / discharge efficiency, and good charge / discharge cycle characteristics. is there.

  The conductive material is for ensuring the electrical conductivity of the positive electrode, and a carbon material powder such as graphite or carbon black can be used. The said powdery body may be used independently and may be used in combination of 2 or more type.

The binder plays a role of connecting the particles of the positive electrode active material and the particles of the conductive material, and is not particularly limited, but is not limited to polytetrafluoroethylene (PTEF) or polyvinylidene fluoride (PVDF). Alternatively, a fluorine-containing resin such as fluororubber, a thermoplastic resin such as polypropylene, or the like can be used.
When PTEF is used as a binder, it is preferably used in combination with polyethylene oxide, PVDF, carboxymethyl cellulose (CMC), which will be a thickener described later, or the like.

The thickener is for imparting viscosity to the positive electrode active material paste, and contains at least a water-soluble polymer, and dissolves in water to give a viscous aqueous solution.
Examples of the water-soluble polymer include polyethylene oxide (PEO), polyvinyl alcohol (PVA), cellulose-based polymer methylcellulose, and a modified form of the methylcellulose. Ethylene oxide (PEO) or a modified form of methyl cellulose, particularly a CMC aqueous solution in which powdered CMC is dissolved in pure water is used.
CMC is particularly preferred as a thickener because it can impart a suitable viscosity and has good dispersibility.

The negative electrode is not particularly limited as long as a negative electrode active material having the characteristics of occluding lithium ions during charging and releasing lithium ions during discharging can be used. Examples of the material having such characteristics include lithium metal, graphite, and carbon materials such as amorphous carbon.
Among them, it is preferable to use a carbon material having a relatively large voltage change with charging / discharging of lithium ions, and it is more preferable to use a carbon material made of natural graphite or artificial graphite having high crystallinity. And the particle | grains of a negative electrode active material are tied together using the binder demonstrated in the positive electrode.

  The separator is for electrically insulating the positive electrode and the negative electrode and holding the non-aqueous electrolyte. Examples of the material constituting the separator include a porous synthetic resin film, particularly a porous film such as a polyolefin-based polymer (polyethylene, polypropylene).

Here, the non-aqueous electrolyte is composed of a non-aqueous solvent and a solute.
As the non-aqueous solvent, carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are preferably used, but are not limited thereto. Further, the non-aqueous solvent can be used alone, but it is preferable to use two or more in combination.
For the solute, a lithium salt such as LiPF ₆ is used.

  A positive electrode and a negative electrode having such a configuration are overlapped or wound via a separator to form an electrode body, and between the positive electrode and the positive electrode terminal connected to the outside from the negative electrode, and the negative electrode terminal, Lithium ion secondary batteries are connected by current collecting lead wires, and the electrode body is inserted and sealed in a battery case while filling a non-aqueous electrolyte between the positive electrode and the negative electrode. Composed.

[Method for producing positive electrode for lithium ion secondary battery]
Next, the manufacturing method of the positive electrode for lithium ion secondary batteries in this invention is demonstrated using FIG. 1 and FIG.
As shown in FIG. 1, the method for manufacturing a positive electrode for a lithium ion secondary battery includes a positive electrode manufacturing process 1 including a paste preparation process 10, a coating process 20, a drying process 30, and a pressing process 40. Embodied (implemented).

The paste preparation step 10 is a step of preparing a positive electrode active material paste by mixing a positive electrode active material and an electrode material such as a thickener.
By applying the positive electrode active material paste prepared in the paste preparation step 10 to the surface of the current collector, a positive electrode in which the positive electrode active material layer is integrally formed can be manufactured.

  The paste preparation process 10 includes a metering process 11, a stirring process 12, a thickener charging process 13, a solvent charging process 14, a dispersing process 15, a binder charging process 16, and a discharging process 17. The positive electrode active material paste is prepared by advancing each of these steps 11, 12,.

  Specifically, first, in the measuring step 11, the required amount of the positive electrode active material, the conductive material, the binder, the thickener, and the like used as the material of the positive electrode active material paste is accurately measured using a measuring machine or the like. Weigh in.

Next, in the stirring step 12, the positive electrode active material, the conductive material, the binder, and the thickening material in a powder state are charged into a dry mixer and sufficiently stirred.
However, the thickener added to the dry mixer in the stirring step 12 is a thickener excluding CMC.
In addition, the binder and the thickener added in the stirring step 12 are mainly in the form of powder, and for the binder, a fluorine-containing resin such as polytetrafluoroethylene (PTEF) is added. For the thickener, polyethylene oxide (PEO) or the like is used.
(Here, the amount of water remaining in the pores of the PEO is smaller than that of CMC, which will be described later, and has little influence on the increase in resistance inside the lithium ion secondary battery. Focusing on the moisture remaining in the pores and reducing the moisture as effectively as possible, the increase in the internal resistance of the lithium ion secondary battery is suppressed as much as possible.)

  When the electrode material (a positive electrode active material in a powder state, a conductive material, a binder, or a thickener) is sufficiently stirred by the stirring step 12, the thickener is In the charging step 13, a CMC aqueous solution is further added to the electrode material as a thickener, and the thickener and the electrode material are mixed.

  Here, the CMC aqueous solution is an aqueous solution in which carboxymethyl cellulose (CMC), which is a cellulosic polymer, is dissolved in pure water, which is a solvent, and a thickener is added to the stirred electrode material. Step 13 includes a manufacturing process for forming a CMC aqueous solution in advance.

  That is, the thickener charging step 13 includes a drying step 13a, a dissolving step 13b, and a charging step 13c so as to be charged into the stirred electrode material after preparing the CMC aqueous solution. Then, by proceeding with these steps 13a, 13b, and 13c in order, the CMC aqueous solution is prepared and charged into the electrode material, and the thickener and the electrode material are mixed.

  Specifically, first, the CMC in a powder state is dried alone at a drying temperature of 265 ° C. or higher and 275 ° C. or lower for a predetermined time by the drying step 13a, and then, the pure C, which is a solvent, is obtained by the dissolving step 13b. Since the dried CMC is charged and dissolved in water to form a CMC aqueous solution, and then the CMC aqueous solution is charged to the electrode material (the powdered electrode material stirred in the stirring step 12) in the charging step 13c. is there.

In addition, it is based on the following reasons about drying CMC in a powder state independently before putting in pure water.
That is, as a factor of deterioration (increase) in internal resistance due to long-term leaving after charging of a large lithium ion secondary battery that has been completed and shipped, it remains in the pores of CMC that is a thickener. Moisture is considered. In order to remove moisture remaining in the pores of the CMC, it is more effective to forcibly dry the CMC alone in the powder state.

Moreover, the drying temperature at the time of drying CMC in a powder state is within a range of 5 ° C. around 270 ° C., that is, 265 ° C. or more and 275 ° C. or less based on the following reasons.
That is, when the moisture remaining in the pores of the CMC is removed by drying with hot air or the like, it is known that when the drying temperature is set to about 270 ° C., the amount of moisture released is the largest, From such a fact, in consideration of changes in the surrounding environment (air temperature, humidity, etc.), the drying temperature is set to 265 ° C. or more and 275 ° C. or less centering on 270 ° C.

  In order to prove the relationship between the drying temperature and the amount of released moisture in the pores of the CMC, an EGA (Evolved Gas Analysis) -MS method, which is a known evolved gas analysis method, is used. Such an experiment was conducted.

First, as a measuring method, powdery CMC is dissolved in ion-exchanged water (pure water), and an appropriate amount of this aqueous solution is applied onto an aluminum foil. Thereafter, the aqueous solution applied on the aluminum foil was dried by applying hot air set at a heating rate of 10 ° C./min, and the powdered CMC was scraped off 100 μg from the aluminum foil. The detection intensity of water (H ₂ O) contained in the gas generated from this powdery CMC was detected.
Here, the "detection intensity", shown in gaseous generated from heated CMC, number of water molecules (H 2 _O molecules) strike the detector, i.e., the number of water molecules (H 2 _O molecules) The greater the value of “detection intensity”, the greater the amount of water (H ₂ O) contained in the gas.
In addition, as an analyzer for performing measurement, GCMS-QP2010 (trade name) manufactured by SHIMADZU was used.

The experimental results obtained by such a measurement method are shown in FIG.
That is, in FIG. 2, the vertical axis represents the detected intensity of water that evaporates (water removed from the pores of the CMC), and the horizontal axis represents the temperature of the hot air (drying temperature) for drying the CMC (unit [° C.]). When the relationship between the two is represented by a curve, when the drying temperature is about 200 ° C., the detected intensity of water that gradually evaporates increases (the amount of water removed from the pores of the CMC increases). When the drying temperature is about 270 ° C., the water detection intensity (the amount of water removed from the pores of the CMC) becomes the maximum value. Thereafter, the moisture detection strength gradually decreases (the amount of water removed from the pores of the CMC decreases), and when the drying temperature reaches around 300 ° C., the moisture detection strength (from the pores of the CMC). It can be seen that the change in the amount of water removed is substantially reduced.

Therefore, according to FIG. 2, the release of moisture remaining in the pores of the CMC in the powder state starts gradually when the drying temperature reaches around 200 ° C., and when the drying temperature reaches 270 ° C., It can be seen that the amount of release reaches the highest value.
When the drying temperature further rises, the amount of water released gradually attenuates. When the drying temperature reaches about 300 ° C., the amount of water released no longer increases even if the drying temperature is increased further. On the contrary, there is a risk that the CMC will ignite.

  Thus, for the formation of the CMC aqueous solution, the CMC in the powder state is dried in advance with hot air at 265 ° C. or higher and within 275 ° C. (drying step 13a), and then the CMC is put into pure water as a solvent. Since it is dissolved (dissolving step 13b), it becomes possible to effectively remove moisture remaining in the pores of the CMC. And the CMC aqueous solution formed by such each process 13a * 13b is thrown into an electrode material (material of the powder state stirred by the stirring process 12), and these thickeners and an electrode material are mixed ( By the charging step 13c), the lithium ion secondary battery can reduce the moisture remaining in the lithium ion secondary battery as much as possible.

  The pure water (solvent) contained in the CMC aqueous solution is so-called externally added moisture to the CMC, and such moisture can be completely removed by the drying step 30 described later. It remains inside the ion secondary battery and does not increase the internal resistance of the lithium ion secondary battery.

When the CMC aqueous solution is introduced into the powdery material (electrode material) made of the positive electrode active material, the conductive material, the binder, the thickener, etc. in the thickener charging step 13, the solvent is subsequently added. In step 14, ion exchange water is introduced into the electrode material.
Here, the ion exchange water is supplied in order to adjust the viscosity of these electrode materials.

  Thereafter, in the dispersion step 15, the electrode material is conveyed to a kneader, and the kneading operation is started so that the positive electrode active material, the conductive material, and the like constituting the electrode material are sufficiently dispersed in the electrode material. .

  In the binder feeding step 16, the binder made of PTFE is further thrown into the electrode material that is being kneaded, and the positive electrode active material, the conductive material, etc. are sufficiently dispersed in the electrode material. When prepared as an active material paste, the kneader stops.

  Thereafter, in the discharge step 17, the prepared positive electrode active material paste is taken out from the kneader, and the paste preparation step 10 ends.

The positive electrode active material paste taken out from the kneader is carried to the coating process 20.
The coating step 20 is a step of applying a positive electrode active material paste to the surface of the current collector.
In the coating step 20, a positive electrode active material layer is formed on the surface of the current collector by applying the positive electrode active material paste to the surface of the current collector.

Thereafter, the current collector coated with the positive electrode active material paste is carried to the drying step 30.
The drying step 30 is a step of drying the positive electrode active material paste applied to the surface of the current collector.
In the drying step 30, the positive electrode active material paste including particles of the positive electrode active material is integrally formed on the surface of the current collector by drying the positive electrode active material paste.
Further, in the pressing step 40, the positive electrode is configured by pressing the current collector on which the positive electrode active material layer is formed.

  Thus, in the present invention, there is provided a method for producing a positive electrode for a lithium ion secondary battery having a paste preparation step 10 for preparing a positive electrode active material paste configured by mixing a positive electrode material, wherein the paste preparation step 10 is a drying step 13a in which CMC of a cellulose polymer is dried in a powder state to remove moisture remaining in pores of the CMC (cellulosic polymer), and the drying step 13a is performed in the drying step 13a. It is provided with a dissolution step 13b for dissolving CMC (cellulosic polymer) in water to generate a thickening material, and a step 13c for mixing the thickening material generated in the dissolution step 13b and an electrode material. Yes.

  The lithium ion secondary battery according to the present invention is a lithium ion secondary battery including a positive electrode configured using a positive electrode active material paste prepared by mixing a positive electrode material, and the positive electrode active material The paste contains a cellulosic polymer from which moisture remaining in the pores has been removed by drying as a thickener.

  By manufacturing a positive electrode for lithium ion secondary batteries using such a manufacturing method, a positive electrode for lithium ion secondary batteries capable of suppressing an increase in internal resistance even after being left for a long time after shipment is realized. can do.

That is, as shown in FIG. 3, for a conventional positive electrode for a lithium ion secondary battery, a positive electrode manufacturing process comprising a paste preparation process 50, a coating process 60, a drying process 70, and a pressing process 80. The paste preparation step 50 includes a metering step 51, an agitation step 52, a thickener input step 53, a solvent input step 54, a dispersion step 55, a binder input step 56, and a discharge. And step 57.
However, the CMC aqueous solution charged in the thickener charging step 53 is formed by dissolving powdery CMC in which moisture remains in the pores as it is in water (pure water) as a solvent. . Therefore, even if the positive electrode active material paste is dried in the drying step 70, the water remaining in the pores of the CMC cannot be removed.

Therefore, as shown in FIG. 1, in the method for producing a positive electrode for a lithium ion secondary battery according to the present invention, the positive electrode active material, the conductive material, the binder, the thickener, and the thickener addition step 13. The CMC aqueous solution charged into a powdery material (electrode material) made of the above is dried in advance in a powder state before being charged into water (pure water) as a solvent.
Therefore, it is possible to effectively remove moisture remaining in the pores of the CMC, and as a result, moisture remaining in the lithium ion secondary battery can be reduced as much as possible.
Therefore, to realize a positive electrode for a lithium ion secondary battery that eliminates deterioration of battery performance, which is considered to be caused by residual moisture, and can suppress an increase in internal resistance even when left for a long time after shipment. Can do it.

In the present invention, the drying temperature in the drying step 13a is 265 ° C. or higher and 275 ° C. or lower.
That is, the drying temperature of the cellulosic polymer contained in the positive electrode of the lithium ion secondary battery in the present invention is set to 265 ° C. or higher and 275 ° C. or lower.

By manufacturing a positive electrode for a lithium ion secondary battery by such a manufacturing method, moisture remaining in the pores of CMC can be more effectively removed.
That is, as described above, when moisture remaining in the pores of the CMC is removed by drying with hot air or the like, when the drying temperature is set to about 270 ° C., the amount of released moisture is the largest. I know.
Therefore, from such a fact, in consideration of changes in the surrounding environment (temperature, humidity, etc.), the CMC is dried at a drying temperature comprised between 265 ° C. and 275 ° C., mainly 270 ° C. The water remaining in the pores of CMC can be removed more effectively.

Furthermore, in the present invention, the cellulosic polymer is carboxymethyl cellulose (CMC).
That is, the cellulose polymer contained in the positive electrode of the lithium ion secondary battery in the present invention is carboxymethyl cellulose.

  By manufacturing a positive electrode for a lithium ion secondary battery by such a manufacturing method, a lithium ion secondary battery using a CMC aqueous solution that is particularly preferable as a thickener, even in a long-term leaving state after shipment, A positive electrode for a lithium ion secondary battery capable of suppressing an increase in internal resistance can be realized.

10 Paste preparation process 13a Drying process 13b Dissolution process 13c Input process

Claims (6)

A method for producing a positive electrode for a lithium ion secondary battery having a paste preparation step of preparing a positive electrode active material paste configured by mixing electrode materials of a positive electrode,
The paste preparation step includes
A drying step of drying the cellulosic polymer in a powder state to remove moisture remaining in the pores of the cellulosic polymer;
Dissolving the cellulosic polymer dried in the drying step in water to produce a thickener; and
Mixing the thickener and electrode material generated in the dissolving step;
Comprising
The manufacturing method of the positive electrode for lithium ion secondary batteries characterized by the above-mentioned. The drying temperature in the drying step is 265 ° C. or more and 275 ° C. or less.
The manufacturing method of the positive electrode for lithium ion secondary batteries of Claim 1 characterized by the above-mentioned. The cellulosic polymer is carboxymethyl cellulose.
The manufacturing method of the positive electrode for lithium ion secondary batteries of Claim 1 or Claim 2 characterized by the above-mentioned. A lithium ion secondary battery comprising a positive electrode configured using a positive electrode active material paste prepared by mixing a positive electrode material,
The positive electrode active material paste is
Cellulose polymer from which moisture remaining in the pores has been removed by drying is included as a thickener.
The lithium ion secondary battery characterized by the above-mentioned. The drying temperature of the cellulosic polymer is 265 ° C. or more and 275 ° C. or less.
The lithium ion secondary battery according to claim 4. The cellulosic polymer is carboxymethyl cellulose.
The lithium ion secondary battery according to claim 4 or claim 5, wherein:

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