JPH01267953A - Manufacture of positive electrode for lithium battery - Google Patents

Abstract

PURPOSE:To provide possibility of coating on a current collector with a certain viscosity without causing dispersion of the viscosity by adjusting the internal temp. of a mixture in accordance with the temp. of pure water, and setting the temp. of the knead black mix between 15 and 19 deg.C. CONSTITUTION:The internal temp. of a mixture is adjusted according to the temp. of pure water, and the temp. of kneaded black mix is set to 15-19 deg.C. Accordingly kneading is made under the condition, that the temp. of the black mix is held at a temp. below the glass transition point of teflon disversion, and can be finished with much time put in prior to gelling of the black mix. When kneading is completed, the viscosity of the black mix is retained in a certain stable condition. Thereafter the temp. rises slowly till the time of coating on the material to current collector, and associate therewith the viscosity of the knead black mix rises, wherein dispersion of the viscosity in coated condition is very small.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a positive electrode for lithium batteries, and in particular to a method for adjusting the viscosity to a predetermined value in a state in which each particle constituting a positive electrode mixture is uniformly mixed and dispersed. The present invention relates to a method that enables the coating to be applied to a current collector material.

(Prior Art) An industrial method for manufacturing a positive electrode mixture for use in spiral-shaped lithium batteries has conventionally been carried out in the following manner.

■After mixing heat-treated manganese dioxide with graphite and acetylene black as conductive agents, pure water is added and kneaded.
In the final step, a binder such as Teflon dispersion is added and kneaded again to prepare a mixed wire mixture in which manganese dioxide and a conductive agent are bound together by the binder.

■Next, this mixed wire mixture is stored inside the coating device, and while the current collector material wound in a roll is fed out, it is passed through the feed guide provided in the coating device, so that it can be adjusted according to the thickness of the slit in the feed guide. Coat the crosstalk mixture on both sides of the current collector material to a certain thickness.

■After the coated mixture is passed through a drying oven to dry and solidify, the mixture is shaped into a uniform thickness by passing through a press roller, and in this state, it is wound up and placed at the stock position. to hold.

■In the secondary processing step, the positive electrode obtained through the above steps is cut into a predetermined size while sequentially unrolling the rolls held in the stock position, exposing a part of the current collector, and attaching the positive electrode lead plate to this part. By welding them together, the positive electrode for a spiral battery is completed.

(Problem to be solved by the invention) The preparation of the kneading mixture in the step (①) above is generally performed at room temperature, but since the indoor temperature changes depending on the season, time of day, sunlight, etc. conductive agent.

The temperature of the binder etc. varied within a range of 25 parts and 5°C depending on the room temperature.

The problem here is that the glass transition point of Teflon dispersion, which is the binder, is 19°C, and for example, if the temperature of the other object of crosstalk is higher than 19°C,
It tends to gel early after mixing begins, and if it is supplied as is to the coating process, the agglomeration state is uneven, resulting in uneven density in each part, resulting in uneven coating, and peeling during press shaping after drying. It is easy to cause problems such as weight variations due to uneven density.

In order to avoid such problems, the kneading time after adding the Teflon dispersion is currently set within 2 to 4 minutes depending on the room temperature in order to quickly finish the kneading time.

However, in this case, there is a drawback that the distribution of each component is uneven, and even if the crosstalk time is shortened in this way,
Variations in viscosity from lot to lot were likely to occur depending on the ambient temperature.

The present invention has been made in view of the above problems, and even if the crosstalk time is made longer than in the past and the elements constituting the mixture are uniformly mixed and dispersed, variations in viscosity do not occur. The object of the present invention is to provide a method for manufacturing a positive electrode for a lithium battery that can be applied to a current collector with a constant viscosity.

(Means for Solving the Problems) In order to achieve the above object, this invention adds and mixes a conductive agent such as graphite or acetylene black to manganese dioxide, then adds pure water and kneads it, and then binds it. A positive electrode for lithium batteries in which a mixed wire mixture is prepared by adding Teflon dispersion as an agent and combining manganese dioxide and a conductive agent with a binder, and then this mixed wire mixture is applied to a current collector material and dried and solidified. In the manufacturing method, the internal temperature of the mixture was adjusted according to the temperature of the pure water so that the temperature of the mixed wire mixture was set at 15 to 19°C.

The blending ratio of the mixed wire mixture is generally as follows.

Manganese dioxide 100 parts (weight, same below) graphite
6 parts Acetylene black 2 parts Pure water 50 parts Teflon dispersion 7.5 parts Total 165.5 parts In industrial production, if parts are replaced with kg, the amount will be suitable for manufacturing each lot.

The reason for limiting the temperature range of the mixed wire mixture to 15 to 19°C is as follows.

If the temperature exceeds 19°C, the glass transition point of the Teflon dispersion is exceeded as described above, and gelation occurs early.

In addition, if the temperature is below 15°C, there will be almost no aggregation, and the resulting mixture will have too much fluidity.
It is undesirable because it makes it difficult to apply a constant thickness, and it also sticks to the feed guide of the coating device and is difficult to remove. Therefore, it is necessary to maintain the above temperature range.

(Function) According to the above method, the temperature of the crosstalk agent is kept at a temperature below the glass transition point of the Teflon dispersion, and the crosstalk is mixed over time before gelation of the mixture occurs. Can be completed.

At the time of completion of crosstalk, the viscosity of the mixture is maintained at a certain stable state.

Thereafter, by the time of application to the current collector material, the temperature rises slowly, and the viscosity of the kneading agent rises accordingly, but the variation in viscosity in the application state is extremely small compared to conventional methods.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

The process order in FIG. 1 shows the above-mentioned steps ① to ②.

First, 100 parts of manganese dioxide (Mn 02 ) was put into container 1, then 6 parts of graphite (C) and 2 parts of acetylene black (conductive agent) were put into container 1, and then 3 parts of pure water
Add 0 parts and mix and stir thoroughly using stirrer 2.

Next, 20 parts of pure water was poured into the container 1, and the stirrer 2 was added.
Stir to mix through.

This pure water serves as a solvent for uniformly dispersing manganese dioxide, graphite, and acetylene black, and also serves as a temperature regulating medium such as a cooling medium. At least the upper limit is 19℃
The temperature is set so that the lower limit is maintained within a range that does not exceed 15°C and the lower limit does not fall below 15°C.

Note that this set temperature varies depending on the amount handled and the surrounding room temperature.For example, if the surrounding room temperature is constant and the temperature of pure water is constant, the temperature change will be small when the amount handled is large, and the temperature change will be small when the amount handled is large. If the amount is small, the temperature change will be large.

The temperature change also differs depending on whether the temperature gradient with respect to room temperature is small or large. For example, the room temperature is 25℃
If it is set within ±5, the pure water temperature is set taking into consideration the maximum temperature gradient of 30° C. and the minimum temperature gradient of 15° C. (in this case, 0).

Therefore, the initial temperature of pure water is set taking into consideration the amount to be handled and the surrounding room temperature.

In any case, when this invention method is implemented for industrial production, the initial temperature of the pure water should be set to a temperature of 16°C or lower so that the inside of the container 1 is maintained at 15 to 19°C. It has been found that the objective can be achieved.

After the above mixing operation, 7.5 parts of Teflon dispersion (emulsion solution of tetrafluoroethylene) is added and thoroughly kneaded. This mixing time may be a time during which each particle is sufficiently mixed and dispersed, during which time the viscosity increases.

Figure 2 shows the relationship between temperature and aggregation rate when Teflon dispersion is dispersed in pure water.
It has been shown that below 19°C, aggregation hardly progresses, and on the contrary, above 19°C, the rate of agglutination increases rapidly.

Therefore, in the range of 15 to 19[deg.] C., the kneading time for the mixed wire mixture can be adjusted to a sufficient time depending on the temperature gradient. .

In the industrial production method, it is possible to take about 6 to 8 minutes within the above temperature range, which is 2 to 4 times the conventional kneading time (2 to 4 minutes).
Each particle can be uniformly dispersed and mixed.

When the mixed wire mixture has a constant viscosity, it is transferred into a coating device 3 formed in a hopper shape.

A T-current collector material 4 wound into a roll is located above the coating device 3 .

This current collector material 4 is made of wire mesh such as stainless steel, expanded metal, or punched metal, and is drawn out through a feed guide 3a opened at the tip of the coating device 3, and is drawn out according to the gap set in the feed guide 3a. The coating thickness of the coating mixture 5 on both sides of the current collector material 4 is set.

The current collector material 4 leaving the coating device 3 immediately passes through a drying oven 6 in succession. By passing through the drying oven 6, the coating mixture 5 coated on both sides (Ii) is dried and solidified and fixed on both sides of the current collector material 4.

Next, the current collector material 4 passes through a rolling roller 7, whereby the thickness of the coating mixture 5 is made uniform. Thereafter, it is wound up by the winding roller 8, stored in a stock position, and subjected to the secondary processing step (2) described above.

Next, when we compared the positive electrode made by implementing the above method and the positive electrode formed by the conventional method, we found that the following figure 3,
The results shown in FIG. 4 were obtained.

Figure 3 shows the thickness distribution after rolling the mixture with a rolling roller, and while the conventional product varied in the range of 0.75 to 1,05 l111, the thickness distribution of the inventive product was 0. 8
It was found that the thickness ranged from 5 to 0.95 m+*, and the thickness was uniform.

Next, Figure 4 similarly shows the tfI amount distribution after rolling, and while the conventional product has a variation of ±15% with respect to the standard weight, the product of the present invention has a normal variation of ±8%. It was found to be distributed and stable.

Furthermore, the number of defective products due to peeling of the mixture and the number of defective weights due to uneven coating per 1000 products were examined, and the results shown in Table 12 and Table 2 below were obtained.

Table 1 (Number of defects due to mixture peeling) *Defect rate decreased from 10% to 4% Table 2 (Number of defects due to weight defects) *Defect rate decreased from 15% to 4% Note that the overall yield of positive electrode mixture is Conventional 75%
It has been confirmed that this can be improved from 94%.

(Effects of the Invention) As described above in detail using the examples, the method for manufacturing a positive electrode in a lithium battery according to the present invention has the following effects.

The mixture is kneaded while the temperature is kept below the glass transition point of the Teflon dispersion, and the mixing can be carried out over time before the kneading agent gels, so that each particle can be sufficiently uniformly mixed and dispersed.

At the time of completion of kneading, the viscosity of the mixed mixture is kept in a certain stable state, and the temperature rises gradually by the time it is applied to the current collector material, and the viscosity of the mixed mixture increases accordingly. In comparison, the variation in viscosity during application is extremely small.

Therefore, the thickness distribution and weight distribution become uniform, and accordingly, the number of peelings and weight defects can be greatly reduced compared to the conventional method, and the yield can be greatly improved, and uniform products can be obtained.

Further, according to the method of the present invention, it is only necessary to control the temperature of the pure water added according to the working environment temperature, so it can be easily carried out.

[Brief explanation of the drawing]

Fig. 1 is a process explanatory diagram for carrying out the method of the present invention;
Figure 3 is a graph showing the relationship between agglomeration rate and temperature, Figure 3 is a graph comparing the thickness distribution of the mixture after rolling between the conventional and the present invention, and Figure 4 is the graph comparing the weight distribution of the mixture between the conventional and the present invention. This is a graph comparing the invention. 3... Coating device 3a... Feed guide 4...
・Current collector material 5...Coating mixture 6...Drying oven
7...Rolling roller Figure 1

Claims (1)

[Claims] (1) Add and mix conductive agents such as graphite and acetylene black to manganese dioxide, then add pure water and knead.
After that, Teflon dispersion is added as a binder to prepare a kneading agent in which manganese dioxide and a conductive agent are combined with the binder, and this kneading agent is then applied to the current collector material and dried and solidified. A method for producing a positive electrode for a lithium battery, wherein the internal temperature of the mixture is adjusted according to the temperature of the pure water so that the temperature of the kneading agent is 15 to 19°C. manufacturing method.