JPH11297357A - Method for producing polymer lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably producing a polymer lithium ion secondary battery having good battery performance without causing a great change in the composition of a positive electrode mixture and a negative electrode mixture due to gelation. I do. SOLUTION: A sheet-like positive electrode in which a gel-like positive electrode mixture layer is formed on at least one surface of a current collector, and a gel-like negative electrode mixture layer is formed on at least one surface of a current collector. In the method for producing a polymer lithium ion secondary battery having a sheet-shaped negative electrode and a sheet-shaped polymer electrolyte layer, polyvinylidene fluoride is used as a gelling agent in the positive electrode mixture and the negative electrode mixture, and propylene carbonate is used as an electrolyte component. Is used at the temperature of 90 to 120 ° C. when the positive electrode mixture and the negative electrode mixture are gelled by using an electrolytic solution containing as an electrolyte solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polymer lithium ion secondary battery, and more particularly, to a method for producing a polymer lithium ion secondary battery having good battery performance. The present invention relates to a method for manufacturing a secondary battery.

[0002]

2. Description of the Related Art Conventionally, when an electrolyte is solidified, a battery free from liquid leakage can be obtained. Therefore, the battery has been regarded as the ultimate battery. However, the ion conductivity is several orders of magnitude lower than that of a solution type. Due to such problems, it did not reach the appearance of a versatile battery.

However, in recent years, when a polymer is gelled together with an organic solvent-based electrolyte, a polymer electrolyte having a high ionic conductivity and an improved ionic conductivity of about 10 ⁻³ S / cm can be obtained. By using this as an electrolyte of a battery, a battery having good characteristics has been obtained, and thus polymer batteries have come into the spotlight again.

[0004]

In such a polymer lithium ion secondary battery, gelation at the time of manufacturing a positive electrode or a negative electrode is performed by mixing an active material of the positive electrode, the negative electrode, an electrolytic solution, a gelling agent, and the like. It is performed by applying the paste-like electrode mixture to the current collector and heating it.However, since the heating temperature is in the area where the electrolyte solvent evaporates, the appropriateness of the heating temperature affects the quality of the positive and negative electrode compositions. In some cases, resulting in failure to obtain a battery having good performance.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for stably producing a polymer lithium ion secondary battery having good battery performance.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies using differential thermal / thermal balance analysis and battery tests, and as a result, the positive electrode mixture and the negative electrode mixture have been obtained. When using polyvinylidene fluoride as a gelling agent in the agent, and using an electrolyte containing propylene carbonate as an electrolyte solvent as an electrolyte component, and performing gelation of the positive electrode mixture and the negative electrode mixture at 90 to 120 ° C., The present inventors have found that a polymer lithium ion secondary battery having excellent battery performance can be stably obtained, and have completed the present invention.

That is, LiCoO _{2 as} a positive electrode active material, graphite as a negative electrode active material, acetylene black as a conductive material, etc.
It does not decompose or change in the above temperature range,
Evaporation of propylene carbonate or the like as an electrolyte solvent starts in the above temperature range, and when the temperature is higher than 120 ° C., the degree of the evaporation is further accelerated.

On the other hand, polyvinylidene fluoride as a gelling agent has a gel point around 90 ° C. and a melting point around 150 ° C. Therefore, if the temperature is lower than 90 ° C,
If the gelation is insufficient and the temperature is higher than 120 ° C., the composition of the positive electrode and the negative electrode becomes unstable because the electrolyte solvent evaporates rapidly as described above.

Therefore, according to the present invention, 90-
By performing gelation under a temperature condition of 120 ° C., it is possible to stably obtain a gelled positive electrode mixture and a gelled negative electrode mixture having a uniform composition, and a polymer lithium ion secondary battery having good battery performance A battery can be manufactured stably.

This will be described with reference to FIG. FIG.
Fig. 2 shows the results of differential thermal and thermobalance analysis of a positive electrode mixture containing propylene carbonate and polyvinylidene fluoride. As is clear from FIG. 1, it is found that the heat generation accompanying the gelation of polyvinylidene fluoride occurs at around 85 ° C., and the heat absorption accompanying the melting occurs at around 160 to 170 ° C. Further, the weight loss due to the evaporation of propylene carbonate has already started at about 80 ° C., and ends at about 200 ° C. It is apparent from FIG. 1 that the rate of weight loss of propylene carbonate increases as the temperature increases, and the degree of weight loss increases with the temperature higher than 120 ° C. Therefore, a region where gelation can be performed and evaporation of propylene carbonate can be suppressed as much as possible is 90%.
It is clear from FIG.

In fact, 60 ° C., 90 ° C., 110 ° C., 120
If the gelation occurs at each temperature of 150 ° C. and 150 ° C., the difference in the effect becomes remarkable. That is, if gelation is attempted at 60 ° C., sufficient temperature cannot be obtained because the temperature is insufficient. Gelation at 150 ° C. causes drying of the active material due to evaporation of the electrolyte solvent, and the longer the gelation time, the more the drying is accelerated. Further, gelation at 150 ° C. is fast, and uniform temperature control is difficult. In contrast, 90-1
The gelation at 20 ° C. is controllable, and a uniformly gelled positive electrode mixture and negative electrode mixture can be obtained.

[0012]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

Examples for Positive Electrode To 10 g of LiCoO _{2 as a} positive electrode active material, ₂ g of acetylene black as a conductive material, 6 g of an electrolytic solution containing propylene carbonate as an electrolytic solvent and 1.2 g of polyvinylidene fluoride were added and mixed. A paste-like positive electrode mixture was prepared. The electrolytic solution was prepared by mixing LiPF _{6 in} a mixed solvent of propylene carbonate and ethylene carbonate at a volume ratio of 1: 1.
Was dissolved in 1.22 mol / l.

This paste-like positive electrode mixture is applied to one surface of an aluminum foil as a current collector,
It heated at each temperature of 110 degreeC, 120 degreeC, and 150 degreeC for 10 minutes, respectively. The results are shown in Table 1 below. In addition, the battery performance when using them as the positive electrode was investigated,
The results are also shown in Table 1. The battery was composed of the above sheet-shaped positive electrode, 6 g of coke as a negative electrode active material, 0.6 g of acetylene black as a conductive material, and an electrolytic solution 5 containing the same propylene carbonate as that used for the positive electrode as an electrolytic solution solvent.
g and 0.8 g of polyvinylidene fluoride are added and mixed to prepare a paste-like negative electrode mixture, and this paste-like negative electrode mixture is applied to one surface of a copper foil and gelled by heating at 120 ° C. A sheet-like negative electrode obtained by the above, an acrylic monomer mixture composed of tri (ethylene glycol) dimethacrylate, ethylene glycol ethyl carbonate methacrylate and 2-ethoxyacrylate, and benzoyl peroxide and propylene carbonate as polymerization initiators thereof It is a combination of a sheet-like gel electrolyte obtained by heating a mixture of the same electrolyte solution as described above containing as an electrolyte solvent, and polymerizing the monomer and gelling the mixture. For comparison, charge at 20 ° C, CCCV to 4.2V at 0.5C, and CV at 0.5C. Discharged to 2.75 V, it was carried out by comparing the cycle characteristics.

[0015]

[Table 1]

Example of Negative Electrode An electrolytic solution containing 6 g of coke as the negative electrode active material, 0.6 g of acetylene black as a conductive material, and propylene carbonate similar to that used for the positive electrode as an electrolytic solution solvent.
g and 0.8 g of polyvinylidene fluoride were added and mixed to prepare a paste-like negative electrode mixture.

This paste-like negative electrode mixture is applied to one surface of a copper foil as a current collector,
It heated at each temperature of 120 degreeC, 120 degreeC, and 150 degreeC for 10 minutes, respectively. The results are shown in Table 2 below. Further, the battery performance when these were used as the negative electrode was examined, and the results are also shown in Table 2. In the battery, the above sheet-shaped negative electrode, 10 g of LiCoO _{2 as} a positive electrode active material, ₂ g of acetylene black as a conductive material, 6 g of the same electrolytic solution containing propylene carbonate as an electrolytic solvent, and 1.2 g of polyvinylidene fluoride were used. A paste-like positive electrode mixture is prepared by adding and mixing, and the paste-like positive electrode mixture is applied to one surface of an aluminum foil, and heated at 120 ° C. to be gelled to obtain a sheet-like positive electrode mixture. A positive electrode, an acrylic monomer mixture composed of tri (ethylene glycol) dimethacrylate, ethylene glycol ethyl carbonate methacrylate and 2-ethoxy acrylate, and benzoyl peroxide and propylene carbonate, which are polymerization initiators thereof, as described above containing an electrolyte solvent Heating the mixture of electrolytes to polymerize the monomers Together are those formed by combining the obtained sheet-shaped gel electrolyte by gelling, comparison of the cell performance, 2
The battery was charged to 4.2 V by CCCV at 0.5 ° C. at 0 ° C.
This was performed by discharging the battery to CV at 2.75 V at 5 C and comparing the cycle characteristics.

[0018]

[Table 2]

As is evident from the results shown in Tables 1 and 2, when the gelation temperature is too low, gelation cannot be performed sufficiently, so that the adhesion between the electrode and the current collector becomes insufficient. If the electrode is peeled off from the current collector and the battery performance is not obtained, and if the gelling temperature is too high, evaporation of the electrolyte solvent such as propylene carbonate is caused, and drying of the active material and the like occurs. As a result, the conduction of ions became insufficient, and charging and discharging became impossible.

[0020]

As described above, the present invention provides a polymer lithium ion secondary battery having good battery performance by gelling the positive electrode mixture and the negative electrode mixture at 90 to 120 ° C. I was able to.

Further, according to the present invention, since the composition of the positive electrode mixture and the negative electrode mixture does not greatly change due to gelation, a polymer lithium ion secondary battery having good battery performance can be stably manufactured. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of differential thermal analysis and thermobalance analysis of a positive electrode mixture.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Eri Yokoyama 1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Taku Sugiyama 1-88 Ushitora, Ibaraki City, Osaka Prefecture Hitachi Maxell Co., Ltd. (72) Inventor Tetsuo Kawai 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd.

Claims (1)

[Claims] 1. A sheet-like positive electrode in which a gel-like positive electrode mixture layer is formed on at least one surface of a current collector, and a gel-like negative electrode mixture layer is formed on at least one surface of a current collector. In a method for producing a polymer lithium ion secondary battery having a sheet-shaped negative electrode and a sheet-shaped polymer electrolyte layer, polyvinylidene fluoride is used as a gelling agent in the positive electrode mixture and the negative electrode mixture, and propylene is used as an electrolyte component. A method for producing a polymer lithium ion secondary battery, comprising using an electrolytic solution containing carbonate as an electrolytic solution solvent and gelling the positive electrode mixture and the negative electrode mixture at 90 to 120 ° C.