CN103748245A - Aluminum alloy plate material for lithium ion battery cases - Google Patents

Abstract

The invention provides an aluminum alloy plate for a lithium-ion battery casing that can reduce the driving pressure of an explosion-proof valve and has excellent laser weldability. %, Cu, Mn, Mg, and Zn as impurities are respectively controlled below 0.10%, and the balance is composed of Al and unavoidable impurities, and more than 1000 pieces/μm3 are distributed in the matrix. The equivalent circle diameter is 5-30nm Al-Fe intermetallic compound, and the thickness of the original plate before cold stamping is set as T0, the thickness after cold stamping is set as T1, and the degree of cold stamping R (%)=[(T0- When T1)/T0]×100, when comparing the tensile strength TS70 (MPa) when R is 70% and the tensile strength TS90 (MPa) when R is 90%, (TS70-TS90) exceeds 5 MPa.

Description

Aluminum alloy sheet for lithium-ion battery case

technical field

The present invention relates to an aluminum alloy plate material for a lithium ion battery case that is suitable as a case material for a lithium ion battery used in automobiles, mobile phones, digital cameras, etc., has excellent laser weldability, and can reduce the driving pressure of an explosion-proof valve.

Background technique

Lithium-ion battery case is a combination of can body material formed by deep drawing of aluminum plate or iron plate, and sealing material formed by punching aluminum plate, and after enclosing internal structures such as electrodes, the can body material and sealing material are sealed. Made by laser welding around the joints.

In order to improve the strength of the case, the sealing material is required to have high strength after stamping, large penetration depth during laser welding, and high joint strength. However, on the other hand, lithium-ion batteries are thermally runaway due to overcharging, etc. , an explosion-proof valve (the part where the plate thickness is locally thinned) is provided for the purpose of reducing the internal pressure before the battery ruptures.

As a method of forming the explosion-proof valve, there are methods of integrally forming the sealing material by press processing, and a method of affixing a foil to the perforated sealing material by laser welding or the like, but the latter has disadvantages in terms of cost and safety. The downside, therefore, is that the former method of formation is often the preferred method.

As the material of the sealing material, A1050 or A3003 has been mainly used so far. Although A1050 has excellent processing performance, it has the disadvantages of low strength after processing and poor laser weldability. On the other hand, A3003 has high strength after processing and excellent laser weldability, but the explosion-proof valve part is work-hardened during the stamping process. Therefore, heat treatment is required in order to adjust the driving pressure of the explosion-proof valve, and its cost becomes a prominent problem.

In order to solve these problems, Al-Mn-Si-Fe-based alloys with improved crack growth properties in explosion-proof valve parts, or Al-Mn-Si-Fe alloys with improved laser weldability and reduced work hardening properties have been proposed as aluminum materials for sealing materials. (Excluding the heat treatment process after stamping) Al-Fe-Mn alloys, etc. However, compared with A3003, although the above-mentioned alloy material has improved crack growth and reduced work hardening, and does not require heat treatment after stamping, but due to work hardening, the hardness of the explosion-proof valve part increases, and the explosion-proof The driving pressure of the valve becomes higher than the design pressure, so the required characteristics cannot be satisfied.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2006-037129

Patent Document 2: Japanese Patent No. 4281727

Contents of the invention

The problem to be solved by the invention

In the process of studying to obtain an aluminum material that can overcome the above-mentioned conventional problems of sealing materials, the present inventors found that when the accumulation of dislocations increases due to cold working, the fine metal that is incompatible with the parent phase The inter-compound becomes the annihilation site of dislocations, which can cause work hardening outside the processing area of the explosion-proof valve, and only show a softened state in the processing area of the explosion-proof valve.

The present invention was obtained as a result of further trials and studies based on the above knowledge, and an object of the present invention is to provide an aluminum alloy sheet material for a lithium ion battery case that can reduce the driving pressure of an explosion-proof valve and has excellent laser weldability.

way of solving the problem

In order to achieve the above object, according to the present invention 1, the aluminum alloy plate for lithium ion battery case is characterized in that, in terms of mass %, it contains Fe: 0.5-2.0%, Si: 0.03-0.3%, and Cu as an impurity , Mn, Mg, and Zn are controlled below 0.10% respectively, and the balance is composed of Al and unavoidable impurities, and there are more than 1000 Al-Fe metals with an equivalent circle diameter of 5-30nm per ^μm3 distributed in the matrix In addition, the thickness of the original plate before cold stamping is set as T0, the thickness after cold stamping is set as T1, and the degree of cold stamping R (%)=[(T0-T1)/T0]× At 100, when comparing the tensile strength TS70 (MPa) when R is 70% and the tensile strength TS90 (MPa) when R is 90%, (TS70-TS90) exceeds 5MPa. In addition, in the following description, all alloy components are represented by mass %.

The aluminum alloy plate for lithium ion battery case according to the present invention 2 is characterized in that, in the aluminum alloy plate of the present invention 1, Ti: 0.20% or less, Zr: 0.20% or less, Cr: 0.30% or less 1 or 2 or more elements in the

The aluminum alloy plate for lithium ion battery case according to the present invention 3 is characterized in that, in the aluminum alloy plate of the present invention 1 or 2, B: 5-100 ppm is further contained.

The effect of the invention

According to the present invention, although it will be hardened by work hardening up to about 70% of the cold working degree, it is difficult for the material to be work hardened at a cold working degree of 90% or more in the processing area of the explosion-proof valve, so that it is possible to provide the Aluminum alloy sheets for lithium-ion battery cases that can increase the strength of the body and reduce the driving pressure of the explosion-proof valve, and are especially suitable as aluminum alloy sheets for lithium-ion battery sealing materials.

Detailed ways

Hereinafter, the meaning of the alloy composition of the aluminum alloy plate material for lithium ion battery cases of this invention, and the reason for limitation are demonstrated.

Fe is an important element that forms incompatible and fine Al-Fe-based compounds in the parent phase (matrix), thereby producing the effect of making work hardening difficult in the high workability region. Furthermore, it also has the effect of improving the absorption rate of the YAG laser used for the joining of a lithium ion battery, and increasing the depth of penetration at the time of laser welding. The preferred content is in the range of 0.5 to 2.0%. If it is less than 0.5%, the characteristics of hardening hardening exhibited in the high processing degree area (hereinafter, simply described as "hardening hardening characteristics") and laser welding The penetration depth of Al is not sufficient, and when the content exceeds 2.0%, the stamping workability is reduced due to the formation of coarse intermetallic compounds. The more preferable content range of Fe is 1.0-1.8%.

Si is easily dissolved in the manufacturing process, and when the content exceeds 0.3%, it becomes difficult to exhibit the characteristic that work hardening becomes difficult. On the other hand, Si is an element contained as an unavoidable impurity in aluminum ingots. If the content is controlled to less than 0.03%, it is not preferable to use high-purity aluminum ingots and increase the cost. Therefore, the preferable content range of Si is 0.03-0.3%, and the more preferable content range is 0.05-0.20%.

In the present invention, since Cu, Mn, Mg, and Zn, which are impurities that are easily solid-solved, hinder the development of characteristics that make work hardening difficult, they are preferably controlled to 0.10% or less, more preferably 0.05% or less.

Ti, Zr, Cr, and B can be added for the purpose of preventing fracture during welding (refinement of structure due to nucleation during solidification). The preferred contents are Ti: 0.20% or less, Zr: 0.20% or less, Cr: 0.30% or less, and B: 5 to 100ppm. When the respective upper limits are exceeded, coarse intermetallic compounds will be generated, resulting in stamping Reduced processability.

The size and number of distributions of Al—Fe intermetallic compounds are important elements required to exhibit the characteristic that work hardening becomes difficult. In order to obtain the effects of the present invention, it is preferable to distribute 1000 pieces/μm ³ or more of Al—Fe-based intermetallic compounds having a circle-equivalent diameter of 5 to 30 nm in the matrix. An intermetallic compound having an equivalent circle diameter of more than 30 nm is less likely to become an annihilation site for dislocations, and has little influence on the development of characteristics that make work hardening difficult. When the distribution number of particles with an equivalent circle diameter of 5 to 30 nm is less than 1000/μm ³ , the annihilation sites of dislocations are insufficient, resulting in an insufficient display of the characteristic that work hardening is difficult.

In the manufacturing process of the aluminum alloy plate material for lithium ion battery cases of the present invention, the control of the size and distribution number of the above-mentioned Al—Fe-based intermetallic compound and the reduction of the solid solution amount of Si are important factors. In the manufacturing process, the known semi-continuous casting method can be used for casting, but the homogenization treatment of the ingot is an important process required to promote the fine precipitation of Al-Fe-based intermetallic compounds.

The homogenization treatment is preferably performed in a temperature range of 450 to 540°C. When the temperature is less than 450°C, the precipitation of the Al-Fe intermetallic compound is insufficient, and when the temperature exceeds 540°C, the Al-Fe intermetallic compound aggregates and becomes coarse, and Fe will be solid-dissolved again, which is not preferable. The homogenization treatment time is preferably 3 to 24 hours. If it is less than 3 hours, the precipitation of the Al—Fe-based intermetallic compound will be insufficient, and if it exceeds 24 hours, the production cost will increase. By adopting the above-mentioned homogenization treatment conditions, due to the fine precipitation of Al—Fe-based intermetallic compounds, it is possible to improve the material strength up to a cold working degree of 0 to 70%.

Hot rolling is performed after homogenization. In order to promote the fine precipitation of Al-Fe intermetallic compounds during the hot rolling process, the hot rolling preferably starts at 400-450°C and ends at 200-250°C. When hot rolling ends in this temperature range, the structure after hot rolling becomes a non-recrystallized structure.

In order to improve the property that work hardening becomes difficult, it is preferable to perform intermediate annealing immediately after hot rolling. In the intermediate annealing process, the processing deformation introduced in the hot rolling is used as the precipitation site, and the fineness of the Al-Fe intermetallic compound is precipitated, and at the same time, the precipitation of Si, which is difficult to work hardening, is prevented. By reducing the solid solution of Si amount, which can improve the characteristics of difficult work hardening.

The annealing temperature is preferably 260 to 400°C. When the annealing temperature is lower than 260°C, the precipitation of Al—Fe-based intermetallic compound is insufficient, and when the annealing temperature exceeds 400°C, since Si is in solid solution, the characteristics that the work hardening becomes difficult cannot be sufficiently obtained. The heating rate to the annealing temperature is preferably 20 to 100° C./hour. If the heating rate is less than 20° C./hour, the production cost will increase, which is not preferable. If it exceeds 100° C./hour, the precipitation of Si will be insufficient, and the characteristics of making work hardening difficult cannot be sufficiently obtained. A more preferable heating rate is 30 to 60° C./hour. Regarding the cooling rate, although it has little influence on the development of the characteristic that becomes difficult to work harden, it is necessary to use a batch furnace because of the relationship with the heating rate, so cooling in the furnace can be performed according to a conventional method.

After hot rolling, or after hot rolling and intermediate annealing, cold rolling is performed to obtain a predetermined thickness. The cold rolling can be carried out according to a predetermined method because it has little influence on the development of the work-hardening hardening characteristic.

Final annealing is performed after cold rolling (intermediate annealing for H1n quenching and tempering). Finish annealing and homogenization treatment are parallel, and are important steps necessary to obtain properties that are difficult to work harden. The purpose of final annealing is to promote the increase of elongation through recrystallization, improve the stamping formability, and use the processing deformation introduced in cold rolling as the precipitation site to promote the fine precipitation of Al-Fe intermetallic compounds, and at the same time make it difficult to hinder work hardening The characteristic exhibits the precipitation of Si, thereby reducing the solid solution amount of Si.

The temperature of the final annealing is preferably 260 to 400°C. If the annealing temperature is lower than 260° C., recrystallization is insufficient, press formability decreases, and precipitation of Al—Fe-based intermetallic compounds is insufficient. If it is 400° C. or higher, due to the solid solution of Si, the characteristics that work hardening becomes difficult cannot be sufficiently obtained.

The heating rate to the final annealing temperature is preferably 20 to 100° C./hour. If the heating rate is less than 20° C./hour, the production cost will increase, which is not preferable. If it exceeds 100° C./hour, the precipitation of Si will be insufficient, and the characteristics of making work hardening difficult cannot be sufficiently obtained. Regarding the cooling rate, although it has little influence on the development of hardening hardening characteristics, it is necessary to use a batch furnace due to the heating rate, so cooling in the furnace can be performed according to the conventional method.

The aluminum alloy sheet material for a lithium ion battery case of the present invention can be used for H1n quenching and tempering by performing cold rolling after final annealing according to the required strength level. Even when H1n is tempered, it is not difficult to obtain the characteristics that work hardening becomes difficult, but since the stamping formability decreases with the decrease of elongation, it is necessary to final annealing treatment in consideration of the balance between strength and stamping formability Conditions, cold rolling rate after final annealing are adjusted.

Example

Hereinafter, the description will be made by comparing the examples of the present invention with the comparative examples, so as to actually verify the effect of the present invention. In addition, these Examples are just one embodiment of this invention, and this invention is not limited to these Examples.

Example 1

Aluminum alloys (A to F) having the compositions shown in Table 1 were dissolved, and ingots having a thickness of 500 nm were produced by a semi-continuous casting method. After homogenizing the obtained ingot at 500° C. for 8 hours, planing and removing 8 mm of the rolling surface, then starting hot rolling at 440° C. and terminating hot rolling at 230° C., thereby obtaining a thickness of 5.0mm hot rolled sheet.

Secondly, cold rolling (cold rolling rate 84%) to a thickness of 0.8mm, and then final annealing at 300°C for 3 hours (heating rate 50°C/hour), thereby producing test materials 1 to 6 (quenched and tempered: O material).

Example 2

Aluminum alloy (G) having the composition shown in Table 1 was dissolved, cast, homogenized, and hot-rolled in the same manner as in Example 1, and then heated at 300°C for 3 hours (heating rate: 50°C/hour). Intermediate annealing, followed by cold rolling (cold rolling rate 84%) to a thickness of 0.8mm, and final annealing at 300°C for 3 hours (heating rate 50°C/hour), thus producing test material 7 (quenched and tempered : O material).

Example 3

The aluminum alloy (H) having the composition shown in Table 1 was dissolved, cast, homogenized, and hot-rolled in the same manner as in Example 1, then cold-rolled (36% cold-rolled ratio) to a thickness of 3.2 mm, and then After performing intermediate annealing at 300° C. for 3 hours (heating rate: 50° C./hour), cold rolling (cold rolling ratio: 75%) to a thickness of 0.8 mm produced test material 8 (tempered: H16 material).

Table 1

Comparative example 1

Aluminum alloys (I-M) having the compositions shown in Table 2 were dissolved and cast in the same manner as in Example 1. After homogenizing the obtained ingot at 500° C. for 8 hours, the rolled surface was planed. After cutting and removing 8 mm, hot rolling was started at 440° C., and hot rolling was terminated at 230° C. to obtain a hot-rolled sheet having a thickness of 5.0 mm. In Table 2, values that deviate from the conditions of the present invention are underlined.

Secondly, cold rolling (cold rolling rate 84%) to a thickness of 0.8mm, and then final annealing at 300°C for 3 hours (heating rate 50°C/hour), thereby producing test materials 9-13 (quenched and tempered: O material).

Comparative example 2

The aluminum alloy (N) having the composition shown in Table 2 was dissolved and cast in the same manner as in Example 1. After homogenizing the obtained ingot at 610° C. for 8 hours, it was heated in the same manner as in Example 1. Rolling, cold rolling, and final annealing, thus producing test material 14 (quenched and tempered: O material).

Table 2

Regarding the test materials 1 to 14 obtained in the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 2, the distribution number of intermetallic compounds and work hardening characteristics were evaluated by the following methods. Table 3 shows the evaluation results of the number of intermetallic compound distributions and work hardening characteristics. In Table 3, values that deviate from the conditions of the present invention are underlined.

Evaluation of the distribution number of intermetallic compounds: The distribution number of intermetallic compounds having an equivalent circle diameter of 5 to 30 μm was quantified using a transmission electron microscope. The number of compounds was measured from the bright field image, and the number of compounds per unit volume (μm ³ ) was calculated from the area of the measurement region and the sample thickness of the measurement region. Using the extinction fringes observed in a transmission electron microscope, the sample thickness was calculated from the product of the number of observed fringe patterns and the extinction distance.

Work hardening characteristics: As the aluminum alloy sheet of the present invention, although the cold stamping process reaches about 70% of the working degree, it will undergo work hardening and harden, but in the cold stamping process with the explosion-proof valve processing area, the working degree of more than 90% Work hardening becomes difficult material properties, and the thickness of the original plate before cold stamping is T0, the thickness after cold stamping is T1, and the degree of cold stamping R (%)=[(T0-T1 )/T0]×100, when comparing the tensile strength TS70 (MPa) when R is 70% and the tensile strength TS90 (MPa) when R is 90%, it has the characteristic of (TS70-TS90) exceeding 5 MPa .

Regarding the evaluation of the above-mentioned work hardening characteristics of the test material, the test material was cold-rolled at a workability of 70% and 90%, and the obtained cold-rolled material was subjected to a tensile test (JIS standard), and the workability of 70% was obtained. The difference between the tensile strength TS70 (MPa) and the tensile strength TS90 (MPa) with a working degree of 90%, that is, (TS70-TS90), and a difference exceeding 5 MPa is evaluated as having a characteristic that work hardening becomes difficult.

table 3

As shown in Table 3, the test materials 1 to 8 of the present invention are all Al-Fe intermetallic compounds with an equivalent circle diameter of 5 to 30 nm distributed in the matrix with ^more than 1000 pieces/μm3, and have a cold working degree of 70 Compared with the tensile strength TS70 of %, the tensile strength TS90 of 90% of the cold working degree (explosion-proof valve processing area) is reduced by 10-20MPa, so it has the characteristics of hardening hardening.

On the other hand, since the test material 9 has a large amount of Si, it is inferior in the characteristic that work hardening becomes difficult. Since the amount of Fe in test material 10 was small, the distribution number of intermetallic compounds having an equivalent circle diameter of 5 to 30 μm was small, and the characteristic that work hardening became difficult was poor. In test material 11, since the amount of Fe was large, coarse intermetallic compounds were formed, the work hardening was severe, and the workability was poor. Since the test material 12 has a large amount of Mn, it is inferior in the characteristic that work hardening becomes difficult. Since the test material 13 had a large amount of Cu and Mn, the work hardening was serious, the workability was poor, and the property that work hardening was difficult was also poor. In Test Material 14, since the homogenization treatment temperature was high, the intermetallic compound was coarsened, and Fe was re-solid-dissolved, and these effects resulted in poor characteristics in which work hardening was difficult.

Claims (3)

1. An aluminum alloy plate for a lithium-ion battery housing, characterized in that, Contains Fe: 0.5 to 2.0%, Si: 0.03 to 0.3% by mass %, controls Cu, Mn, Mg, and Zn as impurities to 0.10% or less respectively, and the balance is composed of Al and unavoidable impurities, and Al-Fe intermetallic compounds with an equivalent circle diameter of 5 to 30 nm are distributed in the matrix at 1000 pieces/μm ³ or more, and the thickness of the original plate before cold stamping is set as T0, and the thickness of the plate after cold stamping is T0. When the thickness is set to T1 and the cold stamping processing degree R (%)=[(T0-T1)/T0]×100, the tensile strength TS70 (MPa) when R is 70% and the tensile strength when R is 90% When comparing the tensile strength TS90 (MPa), (TS70-TS90) exceeds 5MPa. 2. The aluminum alloy plate for lithium-ion battery case as claimed in claim 1, characterized in that, The aluminum alloy sheet further contains, by mass %, one or more elements selected from Ti: 0.20% or less, Zr: 0.20% or less, and Cr: 0.30% or less. 3. The aluminum alloy plate for lithium-ion battery case as claimed in claim 1 or 2, characterized in that, The aluminum alloy plate further contains B: 5-100 ppm in mass %.