JP6035058B2 - Aluminum alloy foil - Google Patents

Description

  The present invention relates to an aluminum alloy foil having excellent tensile strength and elongation.

Aluminum alloy foils that serve as electrode substrates for lithium ion secondary batteries are often produced at high speed and line operation with high tension in order to improve productivity in the processing steps from coating to battery assembly. In order to increase the density of the coating layer containing the active material in order to improve the capacity of the battery, a method of pressing the coating layer under high pressure is employed.
On the other hand, it has been known that even if the aluminum alloy foil is manufactured under the same conditions, there is a difference in the tensile strength and elongation of the aluminum alloy foil particularly in summer and winter.

  By the way, even if the conditions in summer and winter are the same, it is thought that the difference in quality occurs due to the influence of outside air temperature, and attempts have been made to control various temperature conditions. For example, controlling the rolling temperature is disclosed in Patent Document 1 by controlling the foil rolling temperature to 70 to 110 ° C., so that dislocation cells, which are metal structures in the aluminum foil material, can be well organized. There is a description that it becomes finer and can prevent an increase in pinholes.

Japanese Patent No. 3529271

  In the above prior art, the rolling up temperature of the material is specified, but the cooling rate from there is not specified. For this reason, it is difficult to obtain an aluminum alloy foil that suppresses the strength reduction of the material even at the same rolling up temperature and exhibits stable tensile strength and elongation throughout the year.

  This invention is made | formed in view of such a situation, and provides the aluminum alloy foil which shows the stable tensile strength and elongation throughout the year.

  According to the present invention, the aluminum purity is 98.0 mass% (hereinafter, mass% is simply referred to as%), and Si: 0.02-0.15%, Fe: 0.03-1.8 %, Cu: 0.002 to 0.05%, and an aluminum alloy foil made of the inevitable impurities of the balance, and the rising temperature after the end of the final rolling is 60 ° C. or higher and 120 ° C. or lower and becomes 40 ° C. The cooling rate is 0.6 (° C./hour) or more and 5.5 (° C./hour) or less, and is defined by the cooling rate / {0.08 × (the rising temperature (° C.)) − 4.18}. An aluminum alloy foil is provided in which the cooling rate index is 0.5 to 1.6.

  The inventors of the present invention have intensively studied to stabilize the tensile strength and elongation of the aluminum alloy foil throughout the year, and at first, by keeping the rolling up temperature and the cooling rate within a certain range, An attempt was made to stabilize the elongation. However, it has been found that at least one of the tensile strength and the elongation may not be improved although the rolling up temperature and the cooling rate are both within the specified range. Then, when the present inventors further examined, the cooling rate index was specified as described above, and by keeping this value within the range of 0.5 to 1.6, the tensile strength of the aluminum alloy foil The inventors have found that the elongation can be stabilized and have completed the present invention.

  Preferably, the aluminum alloy foil has a tensile strength of 175 MPa or more and an elongation of 3% or more and 6% or less.

  Preferably, the aluminum alloy foil has a wet tension of 28 mN / m or more and 35 mN / m or less.

  The present invention will be described in detail below. The aluminum alloy foil of the present invention can be suitably used as various electrode materials such as lithium ion secondary batteries and lithium ion capacitors, and its aluminum purity is 98.0% or more. If the aluminum purity is less than 98.0%, heat transfer is slow due to the small amount of aluminum contained, and the cooling rate described later cannot be controlled to an appropriate value. In one example, the balance excluding Si, Fe, Cu and inevitable impurities may be aluminum.

  Si amount is 0.02 to 0.15%. If the amount of Si is less than 0.02%, it is difficult to obtain a desired tensile strength, and if it exceeds 0.15%, the material becomes too hard and it is difficult to obtain an aluminum alloy foil having a desired elongation. Absent. The amount of Si is more preferably 0.06 to 0.15%, and still more preferably 0.11 to 0.15%.

  The amount of Fe is 0.03 to 1.8%. If the Fe content is less than 0.03%, it is difficult to obtain a desired tensile strength, and if it exceeds 1.8%, the material becomes too hard and it is difficult to obtain an aluminum alloy foil having a desired elongation. Absent. The amount of Fe is more preferably 0.05 to 1.5%, and further preferably 0.1 to 1.2%.

  The amount of Cu is 0.002 to 0.05%. If the amount of Cu is less than 0.002%, it is difficult to obtain the desired tensile strength of the aluminum alloy foil, and if it exceeds 0.05%, the material becomes too hard and an aluminum alloy foil having a desired elongation can be obtained. Since it becomes difficult, it is not preferable. The amount of Cu is more preferably 0.01 to 0.04%, and still more preferably 0.01 to 0.03%.

  The reason why the chemical composition of the aluminum alloy foil is in the above-described range is that when the alloy system is different, the desired excellent tensile strength and elongation can be obtained even if the ascending temperature and the cooling rate after final rolling described later are specified. Becomes difficult.

  The aluminum alloy foil of the present invention can be produced by appropriately selecting homogenization treatment, hot rolling, cold rolling, and intermediate annealing by a normal method, but the rising temperature after the final rolling is 60 ° C. or higher and 120 ° C. or lower. The cooling rate from the rising temperature after the final rolling to 40 ° C. is 0.6 (° C./hour) or more and 5.5 (° C./hour) or less, and the cooling rate / {0.08 × It is necessary to be manufactured under conditions controlled so that the cooling rate index defined by (up temperature (° C.)) − 4.18} is 0.5 to 1.6.

The ascending temperature after the final rolling of the present invention refers to the temperature immediately after the final rolling process adopted as the manufacturing process of the aluminum alloy foil, and is measured by bringing a contact thermometer into contact with the surface of the rolled coil immediately after the final rolling. can do. The rising temperature is 60 ° C. or higher and 120 ° C. or lower, and particularly 70 ° C. or higher and 110 ° C. or lower is recommended from the viewpoint of tensile strength and stability of elongation. If the rising temperature is less than 60 ° C, the elongation becomes insufficient, and if it exceeds 120 ° C, the tensile strength becomes insufficient.
In the present invention, the optimization of the rising temperature can be appropriately adjusted according to the foil thickness at the time of final rolling. For example, in the case of forming as an electrode material, the rising temperature condition can be suitably used when an aluminum alloy foil having a thickness of 0.2 mm or more and 0.5 mm or less is rolled to 0.030 mm at the time of final rolling. .

  The ascending temperature after the final rolling can be performed by appropriately adjusting the rolling conditions during foil rolling, and specifically corresponds to the material temperature, rolling reduction, rolling speed, rolling oil temperature, and material width of the intermediate path. Examples include the amount of rolling oil.

  In the present invention, the cooling rate of the aluminum alloy foil refers to a rate (° C./hour) calculated from the time required from the rising temperature after the rolling to 40 ° C. in the present invention.

  Here, the reason from the final rolling up temperature to 40 ° C. is that the maximum room temperature of the year is taken into consideration. That is, the decrease to 40 ° C. or less can be approximated to the maximum room temperature of the year and can be maintained at a temperature almost equal to the room temperature, so that the tensile strength and elongation can be maintained without hindrance due to the temperature change on the aluminum alloy foil. .

  The reason why the cooling rate is defined as 0.6 (° C./hour) or more and 5.5 (° C./hour) or less is that the cooling rate index is within the range when the cooling rate is lower than the lower limit of this range. However, if the aluminum alloy foil is too soft and sufficient tensile strength cannot be obtained, and if the cooling rate is higher than the upper limit of this range, the aluminum alloy foil is not sufficiently softened and sufficient elongation is achieved. It is because it cannot be obtained. For this reason, an absolute lower limit and an upper limit of the cooling rate are defined separately from the cooling rate index.

  In the present invention, it is necessary to control the relationship between the ascending temperature after the end of the final rolling and the cooling rate until reaching 40 ° C. by the cooling rate index. The cooling rate index is defined by cooling rate / {0.08 × (the rising temperature (° C.)) − 4.18} and needs to be 0.5 to 1.6. The value of the cooling rate index is defined as 0.5 to 1.6. If this value is less than 0.5, the cooling rate is slow relative to the rising temperature, and the tensile strength of the rolled aluminum alloy foil is low. If this value exceeds 1.6 and the temperature exceeds 1.6, the cooling rate is too high with respect to the rising temperature, and the tensile strength is high but the elongation may be small and insufficient.

  The cooling rate described above can be measured by attaching a thermocouple to the rolled coil after completion of rolling and recording the temperature change with a temperature recorder.

  Any method for increasing the cooling rate of the aluminum alloy foil may be used. For example, a method for cooling the rolling coil by blowing air may be used. By looking at the rolling up temperature and changing the subsequent cooling rate, the total amount of heat immediately after the end of rolling can be made constant even when the rolling up temperature changes, and the tensile strength and elongation of the aluminum alloy foil can be kept constant. The variation can be reduced as much as possible.

  Any method may be used for slowing the cooling rate of the aluminum alloy foil. For example, the aluminum alloy foil may be stored in a warming room kept at a certain temperature.

  As a result, the tensile strength and elongation of the aluminum alloy foil of the present invention have small variations, so that an aluminum alloy foil with stable quality can be obtained.

  The aluminum alloy foil of the present invention preferably has a tensile strength of 175 MPa or more. If the tensile strength is less than 175 MPa, for example, it may be unfavorable because the strength is insufficient and the foil is cut in the coating process, or the foil is broken or bent in the pressing process to reduce the yield. . More preferably, it is 180 MPa or more. The tensile strength can be measured by the method described later. The upper limit of the tensile strength is not particularly specified, but is 200 MPa.

  In the present invention, the elongation of the aluminum alloy foil is preferably 3% or more and 6% or less. If it is less than 3%, for example, the foil may be broken or bent in the pressing process due to insufficient elongation, which may be undesirable. If it exceeds 6%, the elongation becomes too large when used as an electrode material, and wrinkles occur during winding after the pressing process, or when used as an electrode material, individual electrode capacities vary. Therefore, it is not preferable. The elongation can be measured by the method described later.

  In the present invention, it is preferable that the wetting tension on the surface of the aluminum alloy foil after final rolling is 28 mN / m or more and 35 mN / m or less. If the wet tension on the surface of the aluminum alloy foil after final rolling is less than 28 mN / m, the active material is difficult to apply when used as various electrode materials, or the active material peels off during repeated charging and discharging as a battery. This is not preferable because the possibility of losing is increased. If the wetting tension on the surface of the aluminum alloy foil after the final rolling exceeds 35 mN / m, it is necessary to remove the rolling oil by washing or the like, which is not preferable because the cost increases.

  As described above, the method for producing the aluminum alloy foil of the present invention may be performed by adjusting the predetermined alloy components, the ascending temperature at the time of final rolling, the cooling rate, and the like, and other methods are not particularly limited. It can manufacture by the method of. Specifically, the aluminum alloy foil can be obtained by sequentially subjecting an aluminum ingot obtained by semi-continuous casting to chamfering, homogenization treatment, hot rolling, cold rolling, and foil rolling. Moreover, it may replace with hot rolling of the aluminum ingot by semi-continuous casting, and a continuous cast board may be thrown into the process after cold rolling. In addition, as needed, immediately after hot rolling or in the middle of cold rolling, a rolled sheet is heated at 250 to 450 ° C. for 1 to 10 hours in a batch annealing furnace, or at 380 to 580 ° C. for 1 second to 3 minutes in a continuous annealing furnace. Intermediate annealing may be performed by any of the methods described above, and final annealing may be performed on the aluminum alloy foil that has been rolled.

  As mentioned above, although embodiment of this invention was described, these are illustrations of this invention and various structures other than the above are also employable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these. The embodiment of the present invention described below relates to a positive electrode for a secondary battery including a positive electrode current collector as an electrode material made of an aluminum alloy foil, but the present invention is not limited to the positive electrode material, For example, depending on the type of active material, it can be used for both the negative electrode and the positive electrode, and can also be applied to other uses such as a capacitor for a secondary battery. The following examples show examples in which the aluminum alloy foil of the present invention is applied as a positive electrode.

(Examples and comparative examples)
No. shown in Table 1. An aluminum ingot containing chemical components A to K was manufactured to a thickness of 500 mm by semi-continuous casting at a solidification rate of 50 mm / min. Each aluminum ingot contained 0.05% by weight or less of inevitable impurity components not shown in Table 1. Next, after smoothing the rolling surface of the aluminum ingot by chamfering, the aluminum ingot was homogenized at 520 ° C. for 6 hours, and then hot rough rolling was applied to the aluminum ingot to obtain a rolling rate. The aluminum alloy sheet thus obtained was subjected to hot finish rolling to produce a hot rolled sheet having a thickness of 2 mm. The temperature of the aluminum alloy sheet immediately after completion of hot finish rolling was 350 ° C. in Examples 8 to 10 and Comparative Examples 3 to 8, and 260 ° C. in other cases.

  The aluminum alloy plate after the hot finish rolling is cooled to room temperature, and then the hot rolled plate is cold-rolled to a thickness of 0.65 mm, and then the 0.65 mm thick aluminum alloy plate is 300 Intermediate annealing was performed at 4 ° C. for 4 hours.

  Subsequently, the aluminum alloy sheet was cold-rolled using a normal rolling oil to obtain a 0.3 mm aluminum alloy sheet, and then using the materials at the initial temperature shown in Table 2, the rolling speed, the oil temperature, Foil rolling was performed by controlling the oil flow rate, rolling time, etc., to obtain an aluminum alloy foil for lithium ion secondary batteries having a thickness of 15 μm.

(Material temperature measurement)
About each obtained aluminum alloy foil for lithium ion secondary batteries, the surface temperature before a rolling start was measured first. Next, foil rolling was performed on each aluminum alloy foil for a lithium ion secondary battery, and the foil rolling upstream temperature was measured. These results are shown in Table 2. In addition, a CHINO sheath thermocouple SCHS1-0 (φ1.0 mm) is attached to the center and end of the outermost winding surface of the rolled up aluminum alloy foil coil and the coil core, and a CHINO recorder The temperature was continuously measured using KR3P21-N0A. The rising temperature and the cooling rate were determined based on the temperature obtained by averaging the temperatures measured at these three points. The time when the temperature reached 40 ° C. was read from the recorder, and the cooling rate was determined from the temperature and time after the completion of rolling.

(Tensile strength measurement)
After measuring the thickness of each obtained aluminum alloy foil for lithium ion secondary batteries by a mass method, cut and sampled to a width of 15 mm and a length of 180 mm so that the direction parallel to the rolling direction is the longitudinal direction, According to JIS Z 2241 (2011), using an Instron type tensile tester (AG-5kNX) manufactured by Shimadzu Corporation, crosshead speed: 10 mm / min. A tensile test was conducted under the condition of the distance between chucks: 50 mm, and the tensile strength (MPa) was determined and shown in Table 2.

[Elongation measurement]
Each of the obtained aluminum alloy foils for lithium ion secondary batteries was subjected to a tensile test in accordance with JIS Z 2241 (2011) under the same equipment and conditions as described above, and measured for elongation (%). . Elongation (%) means elongation at break.

(Wetting tension measurement)
In accordance with JIS K6786 (1999), a dedicated indicator was dropped on the surface of each aluminum alloy foil for lithium ion secondary batteries, and the wetting tension was measured.

<Consideration of results>
As shown in Table 2, in Examples 1 to 10, the rising temperature, the cooling rate, and the cooling rate index are all appropriate, and the aluminum alloy foil for the lithium ion secondary battery has a stable tensile strength. In addition, the elongation shows a stable value.
In Comparative Example 1, since the rising temperature was too low, the elongation was not sufficient.
In Comparative Example 2, since the rising temperature was too high, the tensile strength was not sufficient.
In Comparative Example 3, the tensile strength was not sufficient because the amount of Si in the alloy was too small.
In Comparative Example 4, since the amount of Si in the alloy was too large, the elongation was not sufficient.
In Comparative Example 5, the tensile strength was not sufficient because the amount of Fe in the alloy was too small.
In Comparative Example 6, since the amount of Fe in the alloy was too large, the elongation was not sufficient.
In Comparative Example 7, since the amount of Cu in the alloy was too small, the tensile strength was not sufficient.
In Comparative Example 8, elongation was not sufficient because the amount of Cu in the alloy was too large.
In Comparative Example 9, since the cooling rate index was too small, the tensile strength was not sufficient.
In Comparative Example 10, since the cooling rate index was too large, the elongation was not sufficient.
In Comparative Example 11, since the cooling rate index was too small, the tensile strength was not sufficient.
In Comparative Example 12, the tensile strength was not sufficient because the cooling rate index was too small.
In Comparative Example 13, the cooling rate index was too large, so that the elongation was not sufficient.

  From these results, by controlling the rising temperature after rolling generated by friction such as rolls during foil rolling and the subsequent cooling rate, the rolling coil of the aluminum alloy foil is lowered to 40 ° C. immediately after rolling. The change in the amount of heat can be reduced, the change in the structure of the aluminum alloy foil can be prevented, and the tensile strength and elongation after foil rolling can be made within an appropriate range. Even in the summer when the material temperature is high or in the low winter, the change in the material temperature due to room temperature is suppressed, so by applying the conditions of the present invention, there is little variation in tensile strength and elongation, An aluminum alloy foil for a lithium ion secondary battery having stable tensile strength and elongation can be obtained.

Claims (3)

A method for producing an aluminum alloy foil, comprising:
Aluminum purity is 98.0 mass% or more (hereinafter, mass% is simply referred to as%), Si: 0.02 to 0.15%, Fe: 0.03 to 1.8%, Cu: 0.00. Including 002-0.05%, the step of rolling the aluminum alloy consisting of the balance inevitable impurities ,
The ascending temperature after the final rolling is 60 ° C or higher and 120 ° C or lower
The cooling rate until reaching 40 ° C. is 0.6 (° C./hour) or more and 5.5 (° C./hour) or less,
The value of the cooling rate index defined by the cooling rate / {0.08 × (the rising temperature (° C.)) − 4.18} is 0.5 to 1.6 ,
Wherein the tensile strength of the produced aluminum alloy foil is not more than 200 MPa, method of manufacturing an aluminum alloy foil. The method for producing an aluminum alloy foil according to claim 1, wherein the produced aluminum alloy foil has a tensile strength of 175 MPa or more and an elongation of 3% or more and 6% or less. Method for producing an aluminum alloy foil according to claim 1 or claim 2 wetting tension of manufacturing aluminum alloy foil is equal to or less than 28 mN / m or more 35 mN / m.