JP2018041616A - Coating device of electrode paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating device of an electrode paste capable of setting the coating gap to an appropriate value, even when a high viscosity electrode paste is used, while reducing occurrence of manufacturing loss in a preparation stage.SOLUTION: A coating device 1 includes: a coating die 30 discharging an electrode paste; a circulation passage 20 for circulating the electrode paste; a pressure measurement unit 40 for measuring the pressure of the electrode paste in the circulation passage 20; and an interval setting unit 50 for setting a coating gap d on the basis of the measured pressure of the electrode paste. A diameter φ of a pipe 22 in the circulation passage 20 to which the pressure measurement unit 40 is attached is set for a median value μ of the measured value of viscosity of the electrode paste, so as to satisfy the following formula (1): (μ/2000)+5≤φ≤(μ/1000)+10 ... (1), in the formula (1), unit of μ is mPa s, and the unit of φ is mm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrode paste coating apparatus that coats an electrode current collector, which is a precursor of an electrode active material layer, onto an electrode current collector.

In recent years, secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries are preferably used as so-called portable power sources such as personal computers and portable terminals and power sources for driving vehicles. In particular, a lithium-ion secondary battery that is lightweight and obtains a high energy density is a high-output power source (for example, a power source that drives a motor connected to a driving wheel of the vehicle) used in a vehicle such as an electric vehicle or a hybrid vehicle. ) Is becoming increasingly important.
For the electrodes of these secondary batteries, for example, an electrode paste prepared by dispersing an active material in a suitable solvent (for example, water) and kneading is prepared, and the electrode paste is applied to a foil-shaped electrode current collector and dried. It is manufactured by doing.

  When coating such an electrode paste on an electrode current collector, for example, a coating method described in Patent Document 1 is used. This coating method detects the pressure and flow rate of the coating liquid in the circulation circuit that circulates the coating liquid between the coating die and the tank of the coating liquid (electrode paste). Based on this, the viscosity of the coating solution is estimated. Then, based on the correlation between the estimated viscosity and the coating width of the coating die, the initial value of the coating gap, which is the distance between the discharge port of the coating die and the substrate (electrode current collector), is determined. . As a result, at the start of coating the electrode paste, the coating width can be stabilized to the target value at an early stage, and discarded products in the preparation stage can be reduced.

JP 2012-254401 A

  By the way, in recent years, an electrode paste having a high solid content and a high viscosity (viscosity: 8000 to 15000 mPa · s) in which the amount of the solvent is smaller than that in the past in order to shorten the drying time of the electrode paste and improve the electrode production rate. Is used.

However, when such an electrode paste having a high solid content and a high viscosity is used, the measurement result of the pressure (pipe pressure loss) in the circulation path may vary greatly, and it may be difficult to accurately estimate the viscosity of the electrode paste. In such a case, the initial value of the coating gap cannot be set to an appropriate value, and the coating width after the start of coating becomes unstable, or streaks due to air entrainment occur in the electrode paste after coating. As a result, manufacturing loss in the preparation stage may increase.
Furthermore, in recent years, there is a tendency that the coating speed is set to be high in order to improve the production speed, and this is also a cause of an increase in manufacturing loss that occurs after the start of coating until the coating width becomes stable. It has become.

  The present invention has been made in view of such a point, and its main purpose is to set the initial value of the coating gap to an appropriate value even when a high-viscosity electrode paste is used. It is possible to provide an electrode paste coating apparatus that can reduce the production loss in the preparation stage.

  In order to achieve the above object, the present invention provides an electrode paste coating apparatus having the following configuration.

An electrode paste coating apparatus disclosed herein includes a storage tank that stores an electrode paste containing an electrode active material, and a coating die that discharges the electrode paste supplied from the storage tank toward the surface of the electrode current collector. A circulation path for circulating the electrode paste before being supplied to the coating die, a pressure measurement unit for measuring the pressure of the electrode paste in the circulation path, and a pressure of the electrode paste in the circulation path measured by the pressure measurement unit And an interval setting unit for setting an interval between the coating die and the electrode current collector at the start of coating the electrode paste.
In the electrode paste coating apparatus disclosed herein, the diameter φ of the circulation path pipe to which the pressure measuring unit is attached is expressed by the following equation (1) with respect to the median μ of the actual measurement value of the viscosity of the electrode paste. ) Is set to satisfy.
(Μ / 2000) + 5 ≦ φ ≦ (μ / 1000) +10 (1)
In the above formula 1, the unit of μ is mPa · s, and the unit of φ is mm.

  In order to obtain measurement results with little variation in the pressure measurement unit when using high-viscosity electrode paste, the diameter of the piping in the circulation path to which the pressure measurement unit is attached is increased to reduce the sensitivity of the pressure measurement unit. There is a way to make it. However, if the diameter of the piping of the circulation path is made too large, the sensitivity of the pressure measuring unit will be too low, and in this case as well, the pressure of the electrode paste cannot be measured accurately.

The electrode paste coating apparatus disclosed herein takes into account the trade-off relationship regarding the sensitivity of the pressure measurement unit described above, and the median value μ of the measured value of the viscosity of the electrode paste and the diameter φ of the piping of the circulation path (1) is defined.
By determining the diameter φ of the circulation path piping based on the formula (1), the influence of variation in the measurement result of the pressure of the electrode paste can be sufficiently reduced, and the coating gap can be appropriately set. In addition, the sensitivity of the pressure measuring unit can be reduced. Accordingly, even when a high-viscosity electrode paste is used, it is possible to set the coating gap at the start of coating to an appropriate value and reduce the production loss at the preparation stage.

It is a figure which shows schematically the structure of the coating apparatus of the electrode paste which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the pressure loss of a circulation path, and the viscosity of an electrode paste, Comprising: The vertical axis | shaft shows the pressure loss (circulation) at the time of a circulation, and the horizontal axis shows the paste viscosity (mPa * s). It is a graph which shows the relationship between an appropriate gap and the viscosity of an electrode paste, Comprising: A vertical axis | shaft shows the appropriate gap (micrometer) and the horizontal axis shows the paste viscosity (mPa * s). It is a graph which shows the relationship between the appropriate gap and the pressure loss of a circulation path, Comprising: A vertical axis | shaft shows the appropriate gap (micrometer) and the horizontal axis has shown the pressure loss at the time of circulation (kPa). It is a figure which shows schematically the structure of the coating apparatus of the electrode paste which concerns on other embodiment of this invention. It is a graph which shows transition of the coating width at the time of using the coating apparatus of Test Example 15.

  Hereinafter, an electrode paste coating apparatus according to the present embodiment will be described with reference to the drawings.

  In the present specification, the “secondary battery” refers to a chargeable / dischargeable battery including a lithium ion secondary battery, a nickel metal hydride battery, and the like. Further, in this specification, the “active material” refers to a substance (compound) involved in power storage on the positive electrode side or the negative electrode side.

  FIG. 1 is a diagram schematically showing an electrode paste coating apparatus according to this embodiment. As shown in FIG. 1, the coating apparatus 1 according to the present embodiment includes a storage tank 10, a coating die 30, a circulation path 20, a pressure measurement unit 40, and an interval setting unit 50.

  An electrode paste containing an electrode active material is stored in the storage tank 10, and the storage tank 10 and the coating die 30 are connected via a supply pipe 21. The coating die 30 is disposed so as to face the electrode current collector S conveyed on the backup roll 80, and a predetermined coating is provided between the coating die 30 and the electrode current collector S. A gap d is provided.

  In addition, the coating apparatus 1 according to this embodiment includes a circulation path 20 including the supply pipe 21 and the return pipe 22 described above. The return pipe 22 has one end connected to the supply pipe 21 upstream of the coating die 30 and the other end connected to the storage tank 10. Although not shown, a connection portion between the supply pipe 21 and the return pipe 22 is provided with a three-way valve, and the three-way valve is configured to switch between discharge and circulation of the electrode paste. .

And the pressure measurement part 40 which measures the pressure of the electrode paste in circulation is provided in piping (return piping 22 in FIG. 1) of the above-mentioned circulation path 20. The pressure measurement unit 40 according to the present embodiment includes a pair of pressure gauges 41 and 42 and measures the pipe pressure loss of the return pipe 22 based on the difference between the measurement results of the pair of pressure gauges 41 and 42.
Each of the pair of pressure gauges 41 and 42 is connected to the interval setting unit 50. The interval setting unit 50 is provided with a viscosity estimating unit 52 that estimates the viscosity of the electrode paste based on the measurement results of the pressure gauges 41 and 42.
For example, in the viscosity estimation unit 52, the relationship between the pipe pressure loss (circulation pressure loss: kPa) of the return pipe 22 during circulation of the electrode paste and the viscosity of the electrode paste (paste viscosity: mPa · s) as shown in FIG. Is stored in advance, and the viscosity of the electrode paste is estimated from the measurement result of the piping pressure loss based on this data. FIG. 2 shows an example in which the return pipe 22 has a diameter φ of 15 mm and the electrode paste flow rate is 950 g / min.

And the space | interval setting part 50 sets the initial value of the coating gap d based on the viscosity of the electrode paste which the viscosity estimation part 52 estimated.
For example, data indicating the relationship between the viscosity of the electrode paste (paste viscosity: mPa · s) and the appropriate value of the coating gap d (appropriate gap: μm) as shown in FIG. Based on this data, the appropriate value of the coating gap d is calculated from the viscosity of the electrode paste. Then, the distance between the coating die 30 and the backup roll 80 is adjusted so that the calculated appropriate value is obtained, and an initial value of the coating gap d at the start of coating is set.
In FIG. 3, the relationship between the paste viscosity (x) and the appropriate gap (y) is expressed by the following linear function equation (2). The correlation coefficient R ² of the equation (2) is 0.9825. is there. The equation (2) is an example of a relational expression set in the interval setting unit 50, and the coefficient of the expression changes according to the target value of the coating width and the coating die 30.
y = −0.0005x + 74.911 (2)

  And in the coating apparatus 1 which concerns on this embodiment, even if it is a case where a high-viscosity electrode paste is used, in order to estimate the viscosity of an accurate electrode paste, piping of the above-mentioned circulation path 20 is possible. The diameter is set according to the measured value of the viscosity of the electrode paste.

Specifically, in the coating apparatus according to the present embodiment, the diameter φ [mm] of the return pipe 22 to which the pressure gauges 41 and 42 are attached is the median value μ [mPa · s] of the actually measured value of the viscosity of the electrode paste. ] Is set so as to satisfy the following formula (1).
(Μ / 2000) + 5 ≦ φ ≦ (μ / 1000) +10 (1)
The median value μ of the measured value of the viscosity of the electrode paste in the above formula (1) is, for example, the upper limit of the measured value of the viscosity of the electrode paste measured under the condition of a shear rate of 2.51 s ⁻¹ using a general rheometer. It is calculated based on the value and the lower limit value. It is not always necessary to use the value between the upper limit value and the lower limit value as it is as the median value μ, but within a predetermined range (± 100 mPa · s, preferably ± 50 mPa · s).

  As described above, in order to reduce the variation in the measurement result of the pipe pressure loss and reduce the influence of using the high-viscosity electrode paste, the diameter φ of the return pipe 22 to which the pressure measuring unit 40 is attached is increased. Then, there is a method of reducing the sensitivity of the pressure measuring unit 40. However, if the diameter φ of the return pipe 22 is excessively increased, the sensitivity of the pressure measuring unit 40 is excessively lowered, and in this case as well, it is difficult to set the coating gap d to an appropriate value.

  The above equation (1) is a return pipe that reduces the sensitivity of the pressure measuring unit 40 to such an extent that the influence of variations in the measurement result of the pipe pressure loss can be sufficiently reduced and the coating gap d can be appropriately set. The range of the diameter φ of 22 is defined. Since this equation is set based on the median value μ of the measured value of the viscosity of the electrode paste, the coating gap d at the start of coating is an appropriate value even when a high-viscosity electrode paste is used. Therefore, it is possible to reduce the production loss in the preparation stage.

  In the above-described embodiment, since the pressure measuring unit 40 is attached to the return pipe 22, the diameter φ of the return pipe 22 is set based on the formula (1), but based on the formula (1). The diameter setting pipe is not limited to the return pipe. For example, as shown in FIG. 5, when the pressure measuring unit 40 is attached to the supply pipe 21 side, the diameter of the supply pipe 21 is set so as to satisfy the above formula (1). Even when this electrode paste is used, the coating gap d at the start of coating can be set to an appropriate value.

In the embodiment described above, the viscosity of the electrode paste (paste viscosity: mPa · s) is estimated based on the relational expression shown in FIG. 2, and the appropriate gap is calculated from the paste viscosity based on the relational expression shown in FIG. However, as shown in FIG. 4, the relationship between the piping pressure loss of the circulation path 20 and the appropriate value of the coating gap d is examined in advance, and the appropriate value of the coating gap d is directly determined from the measurement result of the piping pressure loss. It may be calculated.
FIG. 4 is a graph showing the relationship between the piping pressure loss in the circulation path during circulation of the electrode paste and the appropriate value of the coating gap, and is obtained by converting the relational expressions shown in FIGS. 2 and 3. The graph shown in FIG. 4 is data in the case where the median value of the measured viscosity of the electrode paste is 10300 mPa · s, and the pipe pressure loss (x) during circulation and the appropriate value (y) of the coating gap Is expressed by the following linear function equation (3). Further, the correlation coefficient R ² of the equation (3) is 0.989.
y = -0.0333x + 75.934 (3)

[Test example]
Hereinafter, although the test example regarding this invention is demonstrated, this test example is not intending limiting this invention.

  In this test example, as shown in Table 1, a plurality of types of electrode pastes having different viscosities are prepared, the upper limit value and the lower limit value of the actual measured values of the viscosity of each electrode paste are measured, and the electrode paste is based on the measurement results. The median value (MPa · S) of the actually measured value of the viscosity was set. Then, a lower limit (φmin) and an upper limit (φmax) of the diameter of the pipe based on the formula (1) are calculated from the set median value, a test example using a pipe having a diameter within the range of φmin and φmax, and φmin And a test example using piping outside the range of φmax.

In this test example, a positive electrode paste (NV value (solid content ratio): 63.5%) containing a lithium transition metal composite oxide was used as the electrode paste, and the flow rate of the positive electrode paste was 1.5 L / min ( The composite weight per unit area was set to 10.2 mg / cm ² .

And before starting the coating of the positive electrode paste, the pipe pressure loss in the circulation path was measured while circulating the positive electrode paste in the circulation path, and the sensitivity of the pressure gauge was obtained based on the measurement result, and the correlation coefficient R ² was calculated. . The results are shown in Table 1.

  Furthermore, after setting the initial value of the coating gap based on the measurement result of the piping pressure loss, the positive electrode sheet was discharged by discharging the positive electrode paste from the coating die while conveying the electrode current collector at a conveying speed of 60 m / min. Production started. At this time, the length (loss length [mm]) of the waste product generated until the desired coating width was obtained was measured, and the case where the measurement result was 3 μm or less was evaluated as “good”. The results are shown in Table 1.

In addition, the setting of the coating gap based on the measurement result of piping pressure loss was performed based on the linear function shown in the following formula (4).
y = −ax + b (4)
y: Appropriate value of coating gap (μm)
a: Sensitivity of pressure gauge b: Arbitrary constant x: Measurement result of piping pressure loss (kPa)

As shown in Test Examples 1, 5, 8, and 11 in Table 1, when the diameter of the pipe is made smaller than the lower limit (φmin) determined by the above equation (1), the sensitivity of the pressure gauge increases. in loss length is greater correlation coefficient R ² decreases. This is considered to be because the influence of the variation in the measurement result of the pipe pressure loss is increased by reducing the diameter of the pipe and increasing the sensitivity too much (sensitivity: 0.06 or more).
On the other hand, as shown in Test Examples 4, 7, and 13, the loss length was also increased when the diameter of the pipe was made larger than the upper limit value (φmax) defined in Equation (1). This is because the pressure gauge sensitivity is less than 0.02 and the piping pressure loss cannot be measured accurately.

On the other hand, in Test Examples 2, 3, 6, 9, 10, and 12 in which the diameter φ of the pipe was set between the lower limit (φmin) and the upper limit (φmax), while obtaining sufficient sensitivity of 0.02 or more, In addition, a high correlation coefficient R ² of 0.98 or more could be obtained. And it confirmed that loss length could be suppressed to 3 mm or less by setting a coating gap based on the computed viscosity and producing a positive electrode sheet.

2. Test B
Next, in order to investigate whether or not the same effect can be obtained even when the flow rate of the positive electrode paste is smaller than that of the test A, the test B was performed.
In Test B, tests were performed under the same conditions as Test A except that the flow rate of the positive electrode paste was changed to 0.6 L / min (Test Examples 14 to 16). Table 2 shows the test conditions and test results of each test example.

  As shown in Table 2, even when the flow rate of the positive electrode paste was changed, the lower limit value (φmin) and the upper limit value (φmax) of the diameter calculated based on the formula (1) as in Test Example 15 It was confirmed that the production loss can be appropriately suppressed by setting the diameter of the piping of the circulation path within the range of.

Furthermore, in Test B, the transition of the coating width immediately after the start of coating in Test Example 15 was examined. The results are shown in FIG. In addition, the dotted line in FIG. 6 has shown the change of the coating gap, and the continuous line has shown the coating width of the positive electrode paste. The horizontal axis indicates the coating time (sec), the right vertical axis indicates the coating width (mm), and the left vertical axis indicates the coating gap (μm). Further, a two-dot chain line in FIG. 6 indicates an upper limit value and a lower limit value of the coating width standard, and a one-dot chain line indicates a median value of the coating width standard.
As shown in FIG. 6, immediately after the start of coating, there was a slight change in either the coating gap or the coating width, but it was always maintained within the standard range of the coating width. Therefore, as in Test Example 15, by setting the diameter of the piping of the circulation path within the range of the lower limit value (φmin) and the upper limit value (φmax) of the diameter calculated based on the formula (1), Since it was possible to apply the electrode paste with an appropriate coating width immediately after the start of the process, it was confirmed that production loss could be appropriately suppressed.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment is only an illustration and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

  According to the technology disclosed herein, secondary batteries for various applications can be manufactured with high productivity. This secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Moreover, the secondary battery obtained by the technique disclosed here can be used in the form of an assembled battery formed by connecting a plurality of them in series and / or in parallel. Therefore, according to the technology disclosed herein, a vehicle (typically an automobile, particularly a hybrid automobile, an electric automobile, a fuel cell automobile, etc.) having such a secondary battery (which may be in the form of an assembled battery) as a power source. This can contribute to the improvement of productivity of automobiles equipped with electric motors.

DESCRIPTION OF SYMBOLS 1 Coating apparatus 10 Storage tank 20 Circulation path 21 Supply pipe 22 Return pipe 30 Coating die 40 Pressure measurement part 41, 42 Pressure gauge 50 Space | interval setting part 52 Viscosity estimation part 80 Backup roll d Coating gap S Electrode current collector

Claims (1)

A storage tank for storing an electrode paste containing an electrode active material;
A coating die for discharging the electrode paste supplied from the storage tank toward the surface of the electrode current collector;
A circulation path for circulating the electrode paste before being supplied to the coating die;
A pressure measuring unit for measuring the pressure of the electrode paste in the circulation path;
Based on the pressure of the electrode paste in the circulation path measured by the pressure measuring unit, an interval setting unit that sets an interval between the coating die and the electrode current collector at the start of application of the electrode paste; An electrode paste coating apparatus comprising:
An electrode paste in which the diameter φ of the piping of the circulation path to which the pressure measuring unit is attached is set so as to satisfy the following formula (1) with respect to the median value μ of the measured value of the viscosity of the electrode paste Coating equipment.
(Μ / 2000) + 5 ≦ φ ≦ (μ / 1000) +10 (1)
In the above formula 1, the unit of μ is mPa · s, and the unit of φ is mm.

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