JP5495694B2 - Aluminum alloy foil for lithium ion secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to an aluminum alloy foil for a lithium ion secondary battery used for a positive electrode material of a lithium ion secondary battery.

  In recent years, lithium ion secondary batteries with high energy density have been used as power sources for portable electronic devices such as mobile phones and notebook computers.

The electrode material of the lithium ion secondary battery includes a positive electrode plate, a separator, and a negative electrode plate. As the positive electrode material, an aluminum alloy foil is used as a support, which is excellent in electric conductivity, does not affect the electric efficiency of the secondary battery, and generates less heat. Generally, JIS 1085 and JIS 3003 aluminum alloys are used. Yes. An active material mainly composed of a lithium-containing metal oxide such as LiCoO ₂ is applied to the surface of the aluminum alloy foil. As a manufacturing method, a press for increasing the density of the active material is further performed through a drying process in which an active material having a thickness of about 100 μm is applied to both sides of an aluminum foil of about 20 μm and the solvent in the active material is removed. I do. The positive electrode plate manufactured in this manner is laminated with the separator and the negative electrode plate, and then wound and stored in the case.

  When the aluminum alloy foil used for the positive electrode material has a large repulsive force when stored in the case and the springback amount is large, the storage property when stored in the case is poor, and there is a gap inside the wound body after storage. There was a problem that the performance deteriorated and the capacity decreased as a result. In addition, when the strength is insufficient, there is a problem that the active material application process causes problems such as deformation, and breakage and cracks are likely to occur, and an aluminum alloy foil having sufficient strength and excellent case storage is desired. ing.

  A document describing the strength of a positive electrode material of a lithium ion secondary battery shows that Patent Document 1 has a tensile strength of 98 MPa or more in order to prevent breakage and cracks during the manufacturing process. However, the strength is not sufficient to prevent breakage and cracks during the manufacturing process.

  Further, Patent Document 2 discloses a method of preventing peeling from an active material without increasing plasticity in the pressure-bonding process by increasing the strength. However, simply increasing the strength causes an increase in yield strength as the tensile strength increases, and therefore, when stored in a case after winding, the repulsive force increases and the swelling increases.

Japanese Patent No. 3444769 JP 2008-150651 A

  The present invention relates to an aluminum alloy foil used for a positive electrode material of a lithium ion secondary battery, and it is difficult to cause defects such as deformation or breakage during application of the active material. An object of the present invention is to provide an aluminum alloy foil for a lithium secondary battery that has a good releasability when housed in a case as a body and thus has good housing properties.

  The present inventors examined aluminum alloy foil used for the positive electrode material of a lithium ion secondary battery. As a result, the Mn-based precipitate distribution is controlled by regulating the components and the production process to an appropriate range, thereby optimizing the proof stress value of the foil after the heat treatment, providing sufficient strength, and an active material The present inventors have found that a foil that does not cause defects such as breakage, cracks, and deformation at the time of application and that has a small amount of springback when formed into a wound body and that is excellent in storage property in a case can be obtained.

The present invention according to claim 1 contains Si 0.01 to 0.60 mass%, Fe 0.2 to 1.0 mass%, Cu 0.05 to 0.50 mass%, Mn 0.5 to 1.5 mass%, with the balance being Al. The tensile strength is 240 MPa or more, the 0.2% proof stress after heat treatment at 100 ° C. for 30 minutes is 270 MPa or less, and the tensile strength after heat treatment at 180 ° C. for 30 minutes is 200 MPa or more. der is, to an aluminum alloy foil for a lithium ion secondary battery having a thickness and wherein 5~30μm der Rukoto.

The present invention according to claim 2 contains Si 0.01 to 0.60 mass%, Fe 0.2 to 1.0 mass%, Cu 0.05 to 0.50 mass%, Mn 0.5 to 1.5 mass%, with the balance being Al. And a step of homogenizing the aluminum ingot made of unavoidable impurities at 520 to 620 ° C. for 1 to 20 hours, and a hot rolling step, and after the homogenization treatment, the rolling start temperature is not cooled below the rolling start temperature. Including a hot rolling stage, a cold rolling stage, an intermediate annealing stage in the middle of the cold rolling stage, and a foil rolling stage. In the cold rolling stage, the rising temperature is 150 ° C. The final rolling rate after the intermediate annealing stage is 45 to 75%, and in the intermediate annealing stage, the cold rolled material is annealed at 300 to 550 ° C. for 1 minute to 3 hours in the batch furnace, and the foil Pressure In the rolling stage, the reduction ratio in one rolling was 50%, and the method for producing an aluminum alloy foil for a lithium ion secondary battery having a thickness of 5 to 30 μm was obtained.

  According to the present invention, it is possible to provide an aluminum alloy foil for a lithium secondary battery that does not cause breakage or peeling of the active material during application of the active material, and has good storage properties when stored in a case as a wound body.

A. Aluminum alloy foil A-1. Composition The composition of the aluminum alloy foil for lithium ion secondary batteries according to the present invention is as follows: Si 0.01 to 0.60 mass%, Fe 0.2 to 1.0 mass%, Cu 0.05 to 0.50 mass%, Mn 0.5 to 1. 5 mass% is contained, and the balance consists of Al and inevitable impurities. In the following, “mass%” is simply referred to as “%”. Inevitable impurities include 0.01% or less of Cr, Ni, Zn, etc. and 0.05% or less of Ti.

Si forms an Al ₁₂ (Mn, Fe) ₃ Si phase (α phase) and contributes to the strength of the aluminum alloy foil. When the Si content is less than 0.01%, it is difficult to realize economically because Si is included as an impurity component in the normally used metal. On the other hand, if it exceeds 0.6%, the distribution density of Mn precipitates increases and work hardening during cold rolling increases. As a result, the yield strength after heat treatment is increased, which is not preferable.

  Fe is also an element contributing to the strength of the aluminum alloy foil. If the Fe content is less than 0.2%, the effect cannot be obtained. On the other hand, if it exceeds 1.0%, the yield strength is increased, the amount of swelling when the wound body is formed becomes large, and the case storage property is deteriorated.

  Cu is also an element that contributes to the strength of the aluminum alloy foil, and suppresses softening in the drying process after application of the active material. If the Cu content is less than 0.05%, the effect cannot be sufficiently obtained. If the Cu content exceeds 0.50%, the yield strength is increased, and the amount of swelling when the wound body is formed becomes large, and the case storage property is deteriorated. .

  Mn is also an element contributing to strengthening of the aluminum alloy foil. If the Mn content is less than 0.5%, the effect of imparting strength cannot be sufficiently obtained, and if it exceeds 1.5%, the yield strength is excessively increased and the case storage property is deteriorated.

A-2. Tensile strength The tensile strength of the aluminum alloy foil for a lithium ion secondary battery according to the present invention is 240 MPa or more. If the pressure is less than 240 MPa, the strength is insufficient, tension is applied during pressing to improve the density of the active material, and cuts and wrinkles are generated. A tensile strength can be 240 Mpa by making a component and a manufacturing process into an appropriate range.

A-3. Yield Strength and Tensile Strength after Heat Treatment As a method for producing the positive electrode plate, drying is performed for the purpose of removing the solvent in the active material. In this drying step, heat treatment is performed at a temperature of about 100 to 180 ° C. Since the aluminum alloy foil used for the positive electrode plate may be softened by this heat treatment to change the mechanical properties, the mechanical properties of the aluminum alloy foil after the heat treatment are important. In the present invention, as the mechanical characteristics, the 0.2% proof stress after heat treatment at 100 ° C. for 30 minutes is 270 MPa or less, and the tensile strength after heat treatment at 180 ° C. for 30 minutes is 200 MPa or more.

  After the positive electrode plate is laminated with the separator and the negative electrode plate, it is wound and stored in the case, but if the proof stress is too large, the amount of spring back when it is used as a wound body increases, so it is difficult to fit in the case storage, After the case is stored, the case swells and deforms. For this reason, the 0.2% yield strength after heat treatment needs to be 270 MPa or less. In addition, when softening occurs in the drying process, the strength is insufficient after forming a wound body, and the active material may be peeled off or a crack may occur due to the active material biting into the aluminum foil. Therefore, it is necessary to make the tensile strength after heat treatment 200 MPa or more.

  The heat treatment is usually performed at 100 to 180 ° C. When the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes is 270 MPa or less, the 0.2% yield strength does not exceed 270 MPa even at higher heat treatment temperatures, and the case has good storage properties. Become. Furthermore, if the tensile strength after heat treatment at 180 ° C. × 30 minutes exceeds 200 MPa, the tensile strength when heat-treated at a temperature lower than 200 MPa does not fall below 200 MPa and prevents cracking. Sufficient strength can be obtained.

B. Manufacturing method of aluminum alloy foil The aluminum alloy for lithium ion secondary batteries which concerns on this invention is manufactured at the following processes using the aluminum ingot of the said alloy composition.

  The aluminum ingot can be melt cast by a conventional method, and a semi-continuous casting method or a continuous casting rolling method can be used. In the semi-continuous casting method, homogenization is performed at 520 to 620 ° C. for 1 to 20 hours. When the homogenization temperature is less than 520 ° C., the distribution density of Mn precipitates is increased, and work hardening during cold rolling is increased, resulting in an increase in yield strength. Moreover, when it exceeds 620 degreeC, local melting | dissolving will occur, surface property will deteriorate or intensity | strength will fall, and since utilization as an aluminum alloy foil becomes difficult once, it is unpreferable. If the homogenization holding time is less than 1 hour, the homogenizing effect is not sufficient, and the distribution density of precipitates is increased, so that the work hardening during cold rolling is increased and the yield strength is increased, which is not preferable. On the other hand, if the time exceeds 20 hours, the distribution density of Mn precipitates is reduced, and the strength after heat treatment is reduced as the base plate strength is lowered.

  In the hot rolling process following the homogenization process, hot rolling is performed at a rolling start temperature of 400 to 600 ° C. without cooling below the rolling start temperature after the homogenization process. When the alloy is cooled to a temperature lower than the hot rolling start temperature after the homogenization treatment, Mn-based precipitates are finely generated. As a result, the work hardening amount in the cold rolling process and the foil rolling process after the hot rolling process is increased, which increases the yield strength, which is not preferable. Depending on the heating conditions of the drying process, the amount of softening may be small, so it is important to control the yield strength not to be too high at the aluminum foil stage.

  Rolling start temperature is 400-600 degreeC. If it is less than 400 degreeC, since the cooling time after completion | finish of homogenization will become long, many Mn precipitates will arise during cooling, the work hardening in cold rolling will increase, and it will raise a yield strength. On the other hand, when the temperature exceeds 600 ° C., the surface properties are deteriorated, which is not preferable. Since the homogenization temperature is 520 to 620 ° C., the rolling start temperature does not actually exceed 600 ° C. Since the distribution density of the generated precipitate is preferably small, it is preferably set to 450 to 600 ° C.

  By controlling the homogenization conditions and hot rolling conditions in this way, the strength increase during cold working is suppressed, so that it is finally possible to obtain an aluminum foil with excellent case storage and softening even in the drying process. The amount can be made appropriate.

The aluminum alloy plate obtained by hot rolling is sequentially subjected to cold rolling and foil rolling to obtain an aluminum foil having a foil thickness of 5 to 30 μm. Cold rolling is performed at a temperature of 150 ° C. or lower, and the final rolling rate after intermediate annealing is 45 to 75%. The final rolling rate after the intermediate annealing is expressed by the following formula. That is, the final rolling rate R ₁ = {(t ₀ −t ₁ ) / t ₀ } × 100 (%). Here, t ₀ is the thickness at the time of intermediate annealing, t ₁ denotes the sheet thickness after the final rolling. Foil rolling is rolling performed when a sheet supplied as a foil is rolled at a rolling reduction of about 50% by one rolling to produce a thin foil. The rolling reduction of foil rolling is expressed by the following formula. That is, the rolling reduction ratio R ₂ = {(t ₁ −t ₂ ) / t ₁ } × 100 (%). Here, t ₂ denotes the foil thickness after one foil rolling, t ₁ is as described above. For the purpose of adjusting the strength of the aluminum alloy foil and controlling the crystal grain size, intermediate annealing may be performed during the cold rolling, and the intermediate annealing is performed at 300 to 550 ° C. for 1 minute in a batch furnace or a continuous furnace. It takes 3 hours.

C. The thickness of the aluminum alloy foil The final thickness of the aluminum alloy foil is 5 to 30 μm. If the thickness is less than 5 μm, breakage or cracks may occur during the manufacturing process, and if it exceeds 30 μm, the volume and weight increase, which is not preferable as a lithium ion secondary battery.

Examples 1-11 and Comparative Examples 12-24
An alloy having a composition shown in Table 1 was melt cast by a semi-continuous casting method to produce an ingot having a thickness of 500 mm. Next, the ingot was subjected to a homogenization treatment under the conditions shown in Table 2 after being chamfered, cooled to a rolling temperature, and hot-rolled to a thickness of 2.5 mm. In Comparative Examples 22 and 23, the mixture was cooled to room temperature after the homogenization treatment. Following cooling after the homogenization treatment, intermediate annealing (batch furnace at 370 ° C. for 2 hours or continuous furnace at 400 ° C. for 30 seconds) is performed under the conditions shown in Table 2 with a sheet thickness of 0.5 mm by cold rolling. Cold rolling (condition: rising temperature 110 ° C.) and foil rolling (condition: rising temperature 110 ° C.) were performed to obtain an aluminum alloy foil sample having a foil thickness of 15 μm.

Using the aluminum alloy foil sample produced as described above, a positive electrode material for a lithium ion secondary battery was produced as follows. A positive electrode slurry was prepared by adding a binder to an active material mainly composed of LiCoO ₂ . The positive electrode slurry was applied to both surfaces of a sample having a width of 30 mm, dried at 150 ° C. for 30 minutes, and then rolled by a roller press to obtain a positive electrode material sample.

  Each aluminum alloy foil sample was evaluated by measuring the tensile strength, 0.2% proof stress after heat treatment at 100 ° C. for 30 minutes, and tensile strength after heat treatment at 180 ° C. for 30 minutes. Furthermore, about each positive electrode material sample, the presence or absence of cutting | disconnection generation | occurrence | production in an active material application | coating process, the presence or absence of active material peeling, and the accommodation property to a case were evaluated. The results are shown in Table 3.

Tensile strength The tensile strength of the aluminum alloy foil sample cut out in the rolling direction was measured using an Instron type tensile tester AG-10kNX manufactured by Shimadzu Corporation. The measurement conditions were a distance between chucks of 50 mm and a crosshead speed of 10 mm / min. Moreover, the aluminum alloy foil sample heat-processed for 30 minutes at 180 degreeC was cut out in the rolling direction, and the tensile strength was measured similarly to the above.

Yield strength An aluminum alloy foil sample heat-treated at 100 ° C. for 30 minutes was cut in the rolling direction, the tensile strength was measured in the same manner as described above, and 0.2% yield strength was obtained from the stress / strain curve.

Storability in case When the 0.2% proof stress after heat treatment at 100 ° C. for 30 minutes is 270 MPa or less, the storability in the case is acceptable (O), and the case where it exceeds it is determined as unacceptable (X). .

Presence / absence of breakage in the active material application process Whether the breakage occurred in the positive electrode material applied in the active material application process was visually observed. The case where cut did not occur was determined to be acceptable, and the case where it occurred was determined to be unacceptable.

Existence of active material peeling The presence or absence of active material peeling was observed visually. The case where peeling did not occur was determined to be acceptable, and the case where at least a portion occurred was regarded as unacceptable.

  In Examples 1 to 11, there was no breakage in the active material application process, no active material peeling, and good storage in the case.

In Comparative Example 12, the alloy composition is outside the range of the present invention, and the amount of Si added is large. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.
In Comparative Example 13, the alloy composition is outside the range of the present invention, and the amount of Fe added is large. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.
In Comparative Example 14, the alloy composition is outside the range of the present invention, and the amount of Fe added is small. As a result, the tensile strength before heat treatment became low, and breakage occurred in the active material application process. Moreover, since the tensile strength after the heat treatment at 180 ° C. for 30 minutes was low and the tensile strength after the drying step was low, some peeling from the active material occurred.
In Comparative Example 15, the alloy composition is outside the scope of the present invention, and the amount of Cu added is large. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.
In Comparative Example 16, the alloy composition is outside the range of the present invention, and the amount of Cu added is low. As a result, the tensile strength before heat treatment became low, and breakage occurred in the active material application process. Further, since the tensile strength after heat treatment at 180 ° C. for 30 minutes was low, the amount of softening in the drying step was large, and the tensile strength after the drying step was low, some peeling from the active material occurred.
In Comparative Example 17, the alloy composition is outside the scope of the present invention, and the amount of Mn added is large. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.
In Comparative Example 18, the alloy composition is outside the range of the present invention, and the amount of Mn added is low. As a result, the tensile strength before heat treatment became low, and breakage occurred when the active material was applied. Moreover, since the tensile strength after the heat treatment at 180 ° C. for 30 minutes was low and the tensile strength after the drying step was low, some peeling from the active material occurred.
In Comparative Example 19, since the homogenization temperature is low, the distribution density of the Mn-based precipitates is high. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.
In Comparative Example 20, since the homogenization time is short, the distribution density of Mn-based precipitates is high. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.
In Comparative Example 21, since the homogenization time is long, the distribution density of Mn-based precipitates is low. As a result, the tensile strength before heat treatment became low, and cuts occurred in the manufacturing process. Moreover, since the tensile strength after the heat treatment at 180 ° C. for 30 minutes was low and the tensile strength after the drying step was low, some peeling from the active material occurred.
In Comparative Example 22, since it was cooled to room temperature after the homogenization treatment, the distribution density of the Mn-based precipitates is high. As a result, the amount of work hardening during cold rolling and foil rolling of the foil increased, the 0.2% proof stress after heat treatment at 100 ° C. × 30 minutes increased, and the case storage property deteriorated.
In Comparative Example 23, since it was cooled to room temperature after the homogenization treatment, the distribution density of the Mn-based precipitates is high. As a result, the amount of work hardening during cold rolling and foil rolling of the foil increased, the 0.2% proof stress after heat treatment at 100 ° C. × 30 minutes increased, and the case storage property deteriorated.
In Comparative Example 24, since the hot rolling start temperature is low, many Mn precipitates are generated during cooling. As a result, the 0.2% yield strength after heat treatment at 100 ° C. for 30 minutes was increased, and the case storage property was deteriorated.

  According to the present invention, it is possible to provide an aluminum alloy foil for a lithium secondary battery that does not cause breakage or peeling of the active material during application of the active material, and has good storage properties when stored in a case as a wound body.

Claims (2)

Si 0.01 to 0.60 mass%, Fe 0.2 to 1.0 mass%, Cu 0.05 to 0.50 mass%, Mn 0.5 to 1.5 mass%, the balance consisting of Al and inevitable impurities, tensile strength Saga and at 240MPa or more, 0.2% proof stress after the heat treatment for 30 minutes at 100 ° C. is not more than 270 MPa, and state, and are at least 200MPa tensile strength after heat treatment for 30 minutes at 180 ° C., the thickness There aluminum alloy foil for a lithium ion secondary battery, characterized 5~30μm der Rukoto. Aluminum ingot containing Si 0.01 to 0.60 mass%, Fe 0.2 to 1.0 mass%, Cu 0.05 to 0.50 mass%, Mn 0.5 to 1.5 mass%, the balance being Al and inevitable impurities Is a step of homogenizing at 520 to 620 ° C. for 1 to 20 hours, and a hot rolling step, and the heat at which the rolling start temperature is 400 to 600 ° C. without cooling below the rolling start temperature after the homogenization treatment Including a cold rolling step, a cold rolling step, an intermediate annealing step in the middle of the cold rolling step, and a foil rolling step , wherein the rising temperature is 150 ° C. or less in the cold rolling step, and after the intermediate annealing step In the intermediate annealing stage, the cold rolled material is annealed in a batch furnace at 300 to 550 ° C. for 1 minute to 3 hours, and in the foil rolling stage, the rolling is performed once. A method for producing an aluminum alloy foil for a lithium ion secondary battery having a thickness of 5 to 30 μm, wherein the rolling reduction is 50% .