Aluminium-based alloy and article made of same

Abstract

The invention relates to metallurgy, and more particularly to aluminium alloys for the manufacture of thin aluminium foils for use in the production of lithium-ion cells and batteries. The present aluminium alloy contains: 0.40–0.60 wt.% iron, 0.10– 0.20 wt.% silicon, 0.05–0.15 wt.% copper, 0.05–0.10 wt.% zirconium, 0.01–0.05 wt.% scandium, 0.005– 0.02 wt.% titanium, 0.0001–0.005 wt.% boron, not less than 99.0 wt.% aluminium, and the remainder unavoidable impurities, including not more than 0.02 wt.% vanadium. The structure of the alloy contains nano-dispersed precipitates of Al3Sc and Al3Zr phases with an L12 crystal structure, as well as complex Al3(Sc,Zr) phases. In a second embodiment, the alloy additionally contains one element selected from the group consisting of: not more than 0.15 wt.% manganese and not more than 0.15 wt.% nickel. The invention provides an increase in ultimate tensile strength to 265-305 MPa and an increase in relative elongation at break to 2-3%.

Description

[0001] ALUMINUM BASED ALLOY AND ITS PRODUCT

[0002] Field of technology to which the invention relates

[0003] The invention relates to the field of non-ferrous metallurgy, namely, to aluminum alloys used for the production of thin aluminum foils for use as electrodes for lithium-ion batteries.

[0004] State of the art

[0005] Aluminum foil is one of the main materials in the production of lithium-ion batteries, which are ultra-thin layers of aluminum foil with a lithium-containing cathode material applied and copper foil with an anode layer.

[0006] Increasing the energy density of a battery can be achieved by increasing the number of layers and the surface area per unit volume, therefore it is necessary to reduce the already small thickness of the foil. Over the years, the thickness of the aluminum foil used has been reduced from 16 µm to 14 µm, and then to 12 µm. Today, many battery manufacturers are switching to using aluminum foil with a thickness of 10 µm and even 8 µm.

[0007] As aluminum foil for lithium-ion batteries gradually becomes thinner, the requirements for tensile strength and surface quality increase proportionally. To prevent ruptures during the processes of applying layers of cathode material, calendering, winding, drying and other technological operations in which the foil is subjected to tensile and compressive forces, the material must have sufficient strength and ductility. For foil with a thickness of 10 μm or less, a strength level of at least 265 MPa with a relative elongation of at least 2% is required. Aluminum foil for lithium-ion batteries is currently made from grades of technical aluminum of the 1xxx series, such as 1070, 1235, 1200, 1100 with an aluminum content of at least 99.0%. The tensile strength in the H18 state is about 180-200 MPa.

[0008] WO2019124530 discloses an aluminum alloy for foil containing (mass %): Fe 1.0 - 1.8, Si 0.01 - 0.06, Cu 0.006 - 0.015, the rest is aluminum and inevitable impurities. This composition allows for obtaining foil for battery electrodes with a thickness of 6 to 30 μm with a tensile strength of up to 180 MPa. The disadvantage of this solution is the insufficient level of strength properties for thin foil.

[0009] An alloy for producing aluminum foil for lithium-ion batteries is known from W02014069119. The alloy contains (wt.%): Fe 0.2 - 1.0, Si 0.1 - 0.6, the rest is Al and inevitable impurities. A variant of this composition with additional alloying of Cu 0.01 - 0.25 wt.% is also known. A method for producing 12 μm thick foil from this alloy is also described. The strength of foil from this alloy is 210 MPa, slightly more than the above-mentioned analog, but not enough for thin foil.

[0010] From JP5639398 a hardened alloy for manufacturing contacts (current collectors) is known. The alloy contains (mass %): Fe 0.2 - 1.3, Cu 0.01 - 0.5, Si up to 0.2, as well as inevitable impurities with residual aluminum of at least 88.0 mass %. Judging by the description of the patent, from this composition it is possible to manufacture foil for current collectors of storage batteries with a thickness of 5 to 20 μm with a tensile strength of 215 - 220 MPa and an elongation of 1 - 3%. Despite the fact that the strength properties of the foil of this version of the aluminum alloy are higher than those of previously described analogs, they are also insufficient for thin foil used as electrodes of storage batteries. High concentrations of alloying elements, especially copper, and, as a consequence, low residual aluminum content, make this alloy unsuitable for the production of thin battery foil, which is mainly made from 1xxx series alloys with an aluminum concentration of at least 99.0 wt.%.

[0011] One of the 1xxx series alloys widely used for the production of battery aluminum foils is alloy 1100, which, in accordance with GOST 618-2014 "Aluminum foil for technical purposes", contains in mass %: total Fe + Si < 0.95, Cu 0.05-0.20, Mn < 0.05, Zn < 0.10, other impurities each individually < 0.05 and a residual Al content of at least 99.0 mass %. The use of this alloy makes it possible to obtain thin foils less than 10 μm thick with a high tensile strength of up to 245 MPa (standard GB / T 33143 "Aluminum and aluminum foils for lithium ion batteries"). However, the production of thin foil with a high level of mechanical properties requires a revision of the composition of this alloy.

[0012] The closest analogue selected as a prototype is the alloy described in WO2019214243 "1100 alloy aluminum foil for lithium battery and manufacturing method therefor", which proposes an aluminum foil based on slag 1100 for lithium batteries, which contains the following components in mass%:

[0013] Fe 0,4-0,5

[0014] Si 0, 1-0, 2

[0015] Si 0.1-0.15

[0016] Ti 0.01-0.02

[0017] Sc 0.03-0.07

[0018] Se 0.03-0.07

[0019] MP < 0.01

[0020] Mg < 0.005

[0021] Zn < 0.005

[0022] Al > 99.2

[0023] Provided that the total content of Fe+Si < 0.65 and the content ratio of Fe / Si are in the range of 2.0-4.0. Compared with the standard alloy 1100, in this invention the total content of Fe and Si is limited so that the secondary iron-containing phases are mainly in the form of the a phase (A^FesSi).

[0024] The addition of rare earth elements Sc and Ce leads to an increase in the mechanical properties of the foil due to the strengthening effect of the precipitation of the AlcCes and ACSc phases. At the same time, rare earth elements can improve the distribution of Fe and Si elements and suppress the precipitation of hard and brittle phases. and FesAl. Thus, according to the known technical solution, it is possible to obtain foil with a thickness of 0.008 to 0.015 mm with a tensile strength of 220 to 260 MPa, a relative elongation of 3.5% to 5% and an electrical conductivity of 32 to 35 MS / m.

[0025] Despite the strength value of 259 MPa achieved according to the description of WO2019214243, this level of mechanical properties does not meet the requirements of lithium-ion battery manufacturers for foils with thicknesses of 10 μm and less, namely, increased mechanical properties, in particular, a tensile strength of at least 265 MPa and a relative elongation at break of at least 2%.

[0026] Disclosure of the essence of the invention

[0027] The technical task and result of the present invention is to obtain aluminum foil from a 1xxx series alloy with an aluminum content of at least 99.0%, used in the production of lithium-ion batteries with thicknesses from 12 to 8 μm and less, with increased mechanical properties, in particular, tensile strength in the range of 265 - 305 MPa and a relative elongation at break of 2 - 3%.

[0028] The problem is solved and the technical result is achieved due to the fact that a new aluminum alloy of the 1xxx series is proposed with additives of iron, silicon, copper, scandium, titanium, boron, which additionally contains zirconium, with the following ratio of components, mass %: iron (Fe) 0.40 - 0.60 silicon (Si) 0.10 - 0.20 copper (Cu) 0.05 - 0.15 zirconium (Zr) 0.05 - 0.10 scandium (Sc) 0.01 - 0.05 titanium (Ti) 0.005 - 0.02 boron (B) 0.0001-0.005 aluminum (Al) not less than 99.0 inevitable impurities, including vanadium (V), the rest, wherein the vanadium content is not more than 0.02, optionally, at least one element selected from the group: manganese (Mn) no more than 0.15 nickel (Ni) no more than 0.15, while in the structure it has nanodispersed precipitates with a LI2 crystal lattice of the A^Sc and ACZr phases, as well as complex Als(Sc,Zr) phases.

[0029] The invention proposes an aluminum alloy of a specific composition, ensuring its use for the production of thin foils used in lithium-ion batteries, with the achievement of a number of non-obvious advantages compared to known analogues.

[0030] Also claimed is a product that is made in the form of a foil from the alloy described above, having a tensile strength of at least 265 MPa and a relative elongation at break of at least 2%.

[0031] Brief description of the drawings

[0032] Fig. 1 shows a photograph of a roll of the obtained foil with a thickness of 8 µm.

[0033] Fig. 2 shows the microstructure of the obtained foil with a thickness of 8 µm.

[0034] Fig. 3 shows a dark-field image of a section of foil obtained in reflection from Als(Zr,Sc) particles. Implementation of the invention

[0035] During the experiments, the component composition of the alloy was selected, and the optimal concentrations and ratios of the components were established to solve the problem and achieve the technical result.

[0036] It has been established that Fe and Si are not only inevitable impurities in the production of primary aluminum, but also the main strengthening elements in first-series aluminum alloys (with an aluminum content of at least 99.0 wt.%). Si dissolves in aluminum in concentrations of up to 1.65 wt.% (at 577 °C), reducing electrical conductivity. Fe, on the contrary, is practically insoluble in aluminum and does not significantly reduce electrical conductivity in low concentrations. Unlike alloy 1100, where the total content of iron and silicon is regulated to be no more than 0.95 wt.%, for the production of higher-strength foil from first-series aluminum, taking into account the use of other strengthening alloying elements, it is necessary to limit the Fe content in the range of 0.40 - 0.60 wt.% and Si in the range of 0.10 - 0.20 wt.%.

[0037] Cu in a concentration of 0.05 to 0.15 wt.% increases the alloy strength due to solid-solution hardening. The use of higher copper concentrations will lead to deterioration of the foil corrosion resistance, which carries the risk of forming corrosion defects when washing the foil from cutting fluids (CL) and applying the cathode material. Also, an increase in the copper concentration in the solid solution will lead to a decrease in ductility in a heavily work-hardened state. For the first series alloy intended for the manufacture of foil for lithium-ion batteries, it is necessary to limit the Cu content to 0.15 wt.%.

[0038] It has also been established that Sc is one of the most effective alloying elements, small additions of which increase the mechanical properties of aluminum. Sc forms a coherent nanodispersed phase AlsSc with aluminum with the structure Ы2. Despite the high efficiency of strengthening aluminum alloys when alloying with Sc, its addition of more than 0.05 wt.% is limited by the very high cost of this element and ligatures based on it.

[0039] The highest strength results are achieved with combined alloying of Sc and Zr, which results in the formation of nanodispersed AI3SC, A^Zr and two-component A13(Zr,Sc) precipitates. In this case, it is necessary to use a two-stage heat treatment for the complete precipitation of nanodispersed Sc / Zr-containing A13(Sc,Zr) particles, in which Sc is precipitated at a temperature above 250 °C, and Zr at a temperature above 400 °C. The use of zirconium makes it possible to reduce the scandium content to values ​​in the range from 0.01 to 0.05 wt.% while maintaining strength properties, but zirconium itself is a refractory metal and its use in concentrations above 0.10 wt.% necessitates the use of higher temperatures during melt casting, which can be difficult on the semi-continuous casting equipment used in industry. Taking into account the above, it is advisable to alloy the alloy with zirconium in the range of 0.05 - 0.10 wt%.

[0040] Additional optional alloying of aluminum alloys Mn in the presence of Fe allows to obtain foils with higher strength and plasticity due to the released intermetallic compounds and an increase in their volume fraction. In the presence of manganese, the intermetallic phase (Fe, Mn)Alb is formed in the cast structure in the form of "rods" with an average diameter of 0.1-1.5 μm. During subsequent rolling, this phase disintegrates into small dispersed particles (Fig. 2), providing an increase in mechanical properties and limiting grain growth during recovery and recrystallization, which leads to an optimal combination of properties in the annealed and incompletely annealed state.

[0041] The additional optional addition of Ni results in the formation of a ternary phase together with iron, which has a favourable morphology and leads to the preservation of plastic properties without significant deterioration of corrosion resistance.

[0042] In this case, alloying with Mn and, to a lesser extent, Ni reduces the electrical conductivity of aluminum, and taking into account alloying with other elements and the need for the content of the main Al to be no less than 99.0% to maintain sufficient conductivity of the cathode aluminum foil, it is necessary to limit the concentration of Mn and Ni to no more than 0.15 wt.% each.

[0043] Ti is widely used in casting aluminum alloys and in quantities of 0.005 - 0.02 wt.% is used as a modifier, allowing for a fine-grained structure during casting due to the formation of compounds with aluminum, which are crystallization centers. At the same time, like Cu, Ti significantly reduces electrical conductivity, so its content must be limited to no more than 0.02 wt.%.

[0044] Also, in order to modify the cast structure and ensure a uniform grain in the foil after deformation, B is introduced in an amount of 0.0001 to 0.005 wt.%, which forms compounds with aluminum that are crystallization centers during casting, ensuring a fine-grained structure in the cast blanks.

[0045] It should be noted that one of the rare earth metals used in alloying aluminum alloys is Ce. For Ce, the low cost is accompanied by rather limited strengthening effects, the insignificant solubility of cerium in the solid state (up to 0.05 wt.%) in aluminum makes strengthening during aging not so effective. Alloying aluminum with this element up to 2 wt.% allows obtaining alloys with improved high-temperature characteristics due to the release of strengthening CeAD particles. Ce additives in concentrations of about 0.05 - 0.07 wt.% do not lead to effective strengthening, while the electrical conductivity of aluminum worsens. Taking into account the use of more effective strengthening alloying elements such as Sc, Zr, Mn and Ni, the use of Ce is not of significant interest, and taking into account the requirements for the 1xxx series for the purity of Al of at least 99.0 wt.%, its presence must be limited to the level of other inevitable impurities.

[0046] Another element that must be limited is V, which is an inevitable impurity in aluminum electrolysis, passing into liquid aluminum from alumina and the anode. Despite the fact that V is used in some aluminum alloys as a modifier or anti-recrystallizer, it can significantly reduce the plasticity of the product. To obtain thin foil with a relative elongation value of at least 2%, it is necessary to separately limit the V content to no more than 0.02 wt.%.

[0047] Examples of the invention

[0048] Samples of aluminum foils with a thickness of 8 to 12 microns with different alloying element contents were manufactured by the method of non-ingot rolling. In factory conditions, rolls of cast blanks of model compositions with a thickness of 8 mm, a width of 1600 mm and a weight of 6-8 tons each were manufactured by the method of semi-continuous casting on a two-roll water-cooled caster. For comparison, a similar roll with a composition taken from the prototype was also manufactured.

[0049] Example 1

[0050] Liquid aluminum grade A8 was used as a raw material for the production of foil rolls alloyed with Sc and Zr. Fe80F, Cu80F, AlScl, Zr80F and crystalline Si were used as a charge material. A1T15B1 rod was used as a modifier. The composition of the melts was controlled by spectral analysis. The composition of the obtained rolls is presented in Table 1. Table 1. Chemical composition of rolls alloyed with Sc and Zr

[0051] The resulting rolls of cast blanks were successively rolled in industrial cold rolling mills using coolant until rolls of foil with a thickness of 12 and 8 µm were obtained (Fig. 1).

[0052] To isolate strengthening nanodispersed Als(Sc,Zr) particles with a crystal lattice structure of the Y2 type during the rolling of the rolls, they were heat treated in the temperature range of 350 - 450 °C (Fig. 3). The results of monitoring the mechanical properties of samples with thicknesses of 12 and

[0053] 8 µm samples taken from foil rolls of model compositions and prototype are presented in Table 2.

[0054] Table 2. Mechanical properties of foil samples alloyed with Sc and Zr with a thickness of 12 and 8 μm The obtained data on mechanical characteristics show that alloying with scandium and zirconium makes it possible to obtain thin foil with a thickness of 8 and 12 µm with a higher level of temporary resistance than the prototype, above 265 MPa (depending on the concentration of alloying elements) and a relative elongation of more than 2%.

[0055] Example 2

[0056] To obtain foil samples alloyed with Mn and Ni both separately and together, four rolls of cast blanks were made. Mn80F and AlNi20% ligatures were used to introduce Mn and Ni into the melt. An AlT15B1 rod was also used as a modifier, introduced during melt casting. The degree of structure modification, as well as the amount of Ti in the alloy, were regulated by the rod feed rate. The composition of the obtained rolls is presented in Table 3. Rolls of thin foil with thicknesses of 8 and 12 μm were made using the technology described in Example 1 (using heat treatments to isolate strengthening nano-dispersed particles with the LI2 structure). The result of measuring the mechanical properties of the obtained foil is presented in Table 4.

[0057] Table 3. Chemical composition of rolls alloyed with Sc and Zr and additionally alloyed with Mn and Ni Table 4. Mechanical properties of foil samples alloyed with Sc and Zr and additionally alloyed with Mn and Ni, 12 and 8 µm thick

[0058] The obtained data indicate that additional alloying with Mn and Ni makes it possible to obtain thin foil with a thickness of 8 and 12 µm with an increased level of strength with a value of temporary resistance in the range of 270 - 300 MPa (depending on the concentration of alloying elements) and a relative elongation of 2%, which also exceeds the level of strength properties of the prototype.

[0059] Example 3

[0060] In the production of aluminum foil in all examples, liquid aluminum of the A8 grade supplied from electrolyzers was used, while the V content in the primary aluminum can vary depending on the purity of the aluminum obtained in the electrolyzer from 0.001 to 0.03 wt.%. To assess the effect of the V impurity on the properties of thin foil, two additional rolls of cast blanks with Sc, Zr, as well as Ni and Mn alloying were produced using liquid aluminum with an increased V content (Table 5). The mechanical properties of foil roll samples of these compositions, obtained using a similar technology described in Example 1, are presented in Table 6. Table 5. Chemical composition of rolls with a high V content

[0061] Table 6. Mechanical properties of foil samples with high V content, 12 and 8 µm thick

[0062] The resulting thin foil, as in the case of Examples 1 and 2, is characterized by increased strength properties exceeding the prototype, but the relative elongation value decreases below 2%. Such a low level of elongation of thin aluminum foil carries the risk of frequent breaks when applying the cathode material of lithium-ion batteries to it, which is a significant drawback.

[0063] The examples provided show that combined alloying of first series aluminum with scandium and zirconium, as well as additional alloying with manganese and nickel, allows obtaining thin foil with an increased level of strength properties and maintaining plasticity, provided that the proposed component ratios are observed, including restrictions on vanadium content. Thus, the value of the ultimate strength of foil made of the alloy of the proposed composition lies in the range of 265 - 300 MPa, and the value of the relative elongation at break is not less than 2%. The obtained level of mechanical properties of the foil of the proposed compositions exceeds the prototype, whose maximum value of ultimate strength, according to the description, is only 260 MPa.

Claims

CLAUSE OF INVENTION 1. An aluminum alloy for the production of thin aluminum foils used in lithium-ion batteries, containing iron, silicon, copper, scandium, titanium, boron, aluminum and unavoidable impurities, characterized in that it additionally contains zirconium, in the following ratio of components, mass %: iron 0.40 - 0.60 silicon 0.10 - 0.20 copper 0.05 - 0.15 zirconium 0.05 - 0.10 scandium 0.01 - 0.05 titanium 0.005 - 0.02 boron 0.0001 - 0.005 aluminum not less than 99.0 unavoidable impurities, including vanadium, the rest, wherein the vanadium content is no more than 0.02, while the alloy structure contains nanodispersed precipitates of the A^Sc and A^Zr phases, as well as complex phases Als(Sc,Zr) with a crystal lattice of the Y2 type.

2. An aluminum alloy for the production of thin aluminum foils used in lithium-ion batteries, containing iron, silicon, copper, scandium, titanium, boron, aluminum and inevitable impurities, characterized in that it additionally contains zirconium and at least one element selected from the group of manganese, nickel, with the following ratio of components, mass %: iron 0.40 - 0.60 silicon 0.10 - 0.20 copper 0.05 - 0.15 zirconium 0.05 - 0.10 scandium 0.01 - 0.05 titanium 0.005 - 0.02 boron 0.0001 - 0.005 manganese no more than 0.15 nickel no more than 0.15 aluminum no less than 99.0 inevitable impurities, including vanadium, the rest, with the vanadium content being no more than 0.02, while the alloy structure contains nanodispersed precipitates of the AI3SC and Al^Zr phases, as well as complex phases Al3(Sc, r) with a Y2-type crystal lattice.

3. An article made of aluminum alloy according to item 1 or item 2, made in the form of foil, having a tensile strength of at least 265 MPa and a relative elongation at break of at least 2%.

4. The product according to item 3, in which the thickness of the foil is less than 12 µm.

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