Battery cell housing made of an aluminum alloy strip with improved weldability and a high recycling content

Abstract

The invention relates to a battery cell housing having an aluminum alloy strip or sheet and to a use of an aluminum alloy strip or sheet for producing a battery cell housing. The aim of the invention is to provide a battery cell housing having an aluminum alloy strip or sheet which allows for high recycling rates, meets the requirements for a battery cell housing, in particular with respect to strength, electrolyte resistance, and electric and thermal conductivity, and can additionally provide a sufficiently large process window for welding methods for producing a battery cell housing that is free of welding defects. This is achieved by a battery cell housing according to patent claim (1) and by a use of an aluminum alloy strip or sheet for producing a battery cell housing according to patent claim (8).

Description

[0001] Battery cell casing made of an aluminum alloy strip with improved weldability and high recycling content

[0002] The invention relates to a battery cell housing comprising an aluminum alloy strip or sheet and to a use of an aluminum alloy strip or sheet for producing a battery cell housing.

[0003] Battery cells are used in a wide variety of technical applications to supply electrical energy to electrical consumers. Applications for battery cells include electromobility, particularly in electric cars, electric bicycles, and electric scooters; consumer electronics, particularly in laptop computers, tablet computers, mobile phones, digital cameras, and video cameras; and energy technology, particularly in battery storage systems, to name just a few. Often, several battery cells are connected in series or parallel to form a battery module or battery system. However, there are also applications in which individual battery cells serve as an energy source.

[0004] Battery cells can generally be divided into primary cells, which can only be discharged once and cannot be recharged, and secondary cells, which are rechargeable. In both primary and secondary cells, the necessary electrochemical processes that enable the battery cell to function can be realized using a variety of different materials. Examples of primary cells in this context are alkaline manganese cells, zinc carbon cells, nickel oxyhydroxide cells, or lithium iron sulfide cells, to name just a few. Examples of secondary cells are lithium ion cells, sodium ion cells, nickel cadmium cells, nickel metal hydride cells, or nickel zinc cells, to name just a few.Lithium-ion secondary cells have been increasingly used in recent years, particularly in the fields of electromobility and consumer electronics, due in part to their comparatively high gravimetric and volumetric energy density. Like other types of battery cells, lithium-ion secondary cells have a battery cell casing. This forms the outer shape of the battery cell and encloses a cavity containing, among other things, the anode material, the cathode material, and an electrolyte. There are various different battery cell casing designs: Cylindrical battery cell casings are essentially cylinder-shaped. If the height of the cylinder is greater than the diameter, they are called round cells; otherwise, they are called button cells. Prismatic battery cell casings are essentially prism-shaped, particularly cuboid-shaped.Another variant is the pouch design, in which the battery cell housing essentially has the shape of a pocket or bag.

[0005] Due to the high demands on strength and mechanical stability, as well as the high demands on electrochemical resistance to the electrolyte, which has a corrosive effect on the battery cell housing, cylindrical battery cell housings in particular have traditionally been made of nickel-plated steel. However, growing cell formats, such as the increasing substitution of 18650 round cells with 21700 round cells and the expected future substitution of 21700 round cells with 4680 round cells or other larger formats in the field of electromobility, place higher demands on electrical and thermal conductivity, as larger amounts of heat are generated that must be dissipated. Potential aluminum materials must also meet the high demands on the strength of the housing material.

[0006] Approaches to the use of aluminum alloys for cylindrical

[0007] Battery cell casings are already known, but are limited to the aluminum alloy AA3003. An example of this is US patent US 6,258,480 B1. For prismatic battery cell casings, however, the aluminum alloy AA3003 is standard, although applications in the field of prismatic cell casings are also limited to this alloy.

[0008] From the US patent application US 2006 / 093908 Al a high-strength battery casing is known, which consists of a composite material with an outer plastic layer and an aluminium foil made of an aluminium alloy of the type AA8079, 1N30, AA8021, AA3003, AA3004, AA3104 or AA3105.

[0009] The identical aluminum alloys are known from the Korean patent application KR 2016005673 A, although the Korean patent application prefers the use of an aluminum alloy of type AA3003.

[0010] The Japanese patent application JP 2015 125886 A focuses on the strength and weldability of the battery casings and proposes the use of aluminum alloys of type AA3003, AA3203, AA3004, AA3104, AA3005 or AA3105.

[0011] However, none of the aforementioned documents addresses the problem of using recycled material, taking into account the additional requirements regarding the strength, electrolyte resistance, electrical and thermal conductivity of the battery cell casing and the weldability of the materials used.

[0012] Sustainability requirements, which have increased significantly in recent years, require the production of battery cell housings with the lowest possible resource use and CCU footprint. The most effective way to achieve this is to reduce the use of energy-intensive primary aluminum by increasing the use of recycled material, also known as secondary aluminum. The latter is obtained by melting down aluminum scrap.

[0013] Aluminum scrap is divided into pre-consumer scrap and post-consumer scrap. Pre-consumer scrap is waste that arises during the production of semi-finished or finished products made of aluminum or aluminum alloys in a variety of possible processes. Pre-consumer scrap can be further divided into internal process scrap, which inevitably arises during the manufacturing process of aluminum strips or sheets, such as sprues, offcuts, chips, production residues, or production rejects, and external process scrap, which inevitably arises during further processing to create the final product, such as punching grids, chips, or production rejects. Post-consumer scrap is end product whose life cycle has been fully completed and which, after use, becomes waste.It is irrelevant whether the waste was used by an end consumer or not, meaning that it could also have been used in an industrial or commercial facility, for example. Examples of post-consumer scrap include food packaging, especially beverage cans, window frames, lithographic printing plate carriers, cable cores, and automotive components.

[0014] The alloy composition of the AA3003 aluminum alloy currently used for battery cell casings is comparatively restrictive according to international specifications, for example, with regard to the standard alloying elements copper, magnesium, chromium, zinc, and titanium. The use of this alloy therefore requires the use of high proportions of primary aluminum, thus hindering the realization of high recycling rates with reduced energy consumption. State-of-the-art battery cell casings made from AA3003 aluminum alloy therefore need to be improved in terms of their sustainability.

[0015] At the same time, welding has emerged as a very important joining technique for the production of battery cell casings, as it is cost-effective and welded joints can meet high sealing and strength requirements. Laser welding, which is generally used without the use of filler metals, is particularly important in this regard.

[0016] However, problems arise when welding metals, especially aluminum alloys, which are critical for the production of battery cell casings. The tendency to hot cracking and the formation of weld pores, which impair the tightness of the battery cell casing, represent defects in the welding process that can render the battery cell casing unusable, i.e., lead to rejects in the production of battery cell casings.

[0017] Hot cracks are cracks in the welded material that can occur immediately after welding due to the shrinkage process of the cooling material, when the stresses occurring during the shrinkage process can no longer be absorbed by the welded material. This can result in a significant loss of strength in the welded joint, which can lead to premature failure of the battery casing. Furthermore, gas tightness may no longer be sufficiently guaranteed if hot cracks form.

[0018] The formation of weld pores, on the other hand, primarily impairs the tightness of the welded joints of the battery cell casings with regard to gas leakage. Both problems can be avoided through the targeted use of process parameters. However, if the possible process window is too narrow, the scrap rate can increase, as certain parameter fluctuations are always present in the welding process. Since the sealing welding of the cell casing body and the lid generally takes place at a late stage of the manufacturing process, in which a significant portion of the value creation has already occurred through the use of expensive chemicals and processes, increased scrap rates cannot usually be tolerated.Against this background, the present invention is based on the object of specifying a battery cell housing comprising an aluminum alloy strip or sheet that enables the realization of high recycling rates, meets the requirements of a battery cell housing, in particular with regard to strength, electrolyte resistance, and electrical and thermal conductivity, and can additionally provide a sufficiently large process window for welding methods for producing battery cell housings free of welding defects. In addition, the present invention is based on the object of specifying a corresponding use of an aluminum alloy strip or sheet for producing a battery cell housing.

[0019] According to a first teaching of the present invention, the above-mentioned object for a battery cell housing comprising an aluminum alloy strip or sheet is achieved in that the aluminum alloy strip or sheet comprises an aluminum alloy with the following alloying constituents in wt.%: 0.1% < Si < 0.7%, 0.2% < Fe < 0.8%, Cu < 0.6%, 0.3% < Mn < 1.5%, 0.01% < Mg < 0.60%, preferably 0.05% < Mg < 0.55%, Cr < 0.25%, Zn < 0.5%, Ti < 0.2%,

[0020] Remainder Al and unavoidable impurities, individually maximum 0.05%, in total maximum 0.15%.

[0021] It has been shown that high recycling contents can lead to increased Si contents in the aluminum alloy. In combination with high Mg contents, however, the tendency of the aluminum alloy to hot crack during welding increases significantly. The process window when using welding processes to manufacture battery cell casings becomes significantly smaller, so that hot cracks can occur after welding. The same applies to the occurrence of weld pores, the formation of which is favored with increasing Mg content due to the low vapor pressure of Mg. The battery cell casing according to the invention, comprising an aluminum alloy strip or sheet with the above-mentioned composition, however, allows the use of very high recycling contents in the production of the aluminum alloy strips. At the same time, higher strengths, in particular higher yield strengths R, are achieved compared to a known AA3003 alloy composition. Po,2 is provided, whereby thinner wall thicknesses of the battery cell housing can be achieved compared to the known AA3003 alloy. Due to the combination of the Si, Fe, Cu and Mg contents according to the invention, the battery cell housing according to the invention is well suited for achieving high recycling rates. This applies in particular to the use of aluminum packaging scrap and UBC scrap (UBC: used beverage can), i.e. beverage cans made of aluminum alloys, which have significant contents of magnesium and copper and are suitable for the production of the aluminum alloy of the aluminum strip or sheet of the battery cell housing. At the same time, a broad process window for welding methods is provided, since the tendency towards hot cracking and the formation of weld pores is reduced by the alloy composition.

[0022] All of the aforementioned advantages are achieved by the alloy composition of the aluminum alloy strip or sheet of the battery cell housing. Furthermore, since the aluminum alloy contains only standard alloying elements, it is also readily recyclable, so that the battery cell housing according to the invention can be easily recycled into existing scrap cycles. Furthermore, the alloy composition results in the electrolyte resistance not being impaired, or not significantly impaired, compared to the already known AA3003 alloy, so that economically and sustainably producible battery cell housings can be provided. According to the invention, the silicon content of the aluminum alloy is in the range 0.1 wt.% < Si < 0.7 wt.%, thus allowing particularly high recycling rates.In one embodiment of the battery cell housing according to the invention, the silicon content of the aluminum alloy is in the range 0.2 wt. % < Si < 0.55 wt. %, preferably 0.35 wt. % < Si < 0.55 wt. %, particularly preferably 0.40 wt. % < Si < 0.50 wt. %. The silicon content of 0.1 wt. % < Si < 0.7 wt. % in combination with the iron and manganese contents according to the invention in the stated amounts leads in particular to relatively uniformly distributed, compact particles of the quaternary a-Al(e,Mn)Si phase. These precipitated particles increase both the strength of the aluminum alloy and its electrical and thermal conductivity because they remove iron and manganese from the solid solution, but without negatively affecting other properties such as corrosion behavior, i.e. electrolyte resistance, or formability. Silicon contents of less than 0.1 wt.-% lead to a reduced precipitation of a-Al(Fe,Mn]Si phases, which can lead to an impairment of the electrical and thermal conductivity due to dissolved manganese. In addition, the absence of a-Al(Fe,Mn]Si phases has a negative effect on tool wear. Silicon contents of more than 0.7 wt.% in combination with magnesium can lead to an increased formation of Mg2Si phases, which negatively affects the solid solution strengthening of the magnesium. The silicon content of the preferred embodiment of 0.2 wt.% < Si < 0.55 wt.%, preferably 0.35 wt.% < Si < 0.55 wt.% and 0.40 wt.% < Si < 0.50 wt.% represents an ideal compromise between high strength, high electrical and thermal conductivity while providing broad process windows for welding.

[0023] According to the invention, the iron content of the aluminum alloy is in the range 0.2 wt.% < Fe < 0.8 wt.%. In one embodiment of the battery cell housing according to the invention, the iron content of the aluminum alloy is in the range 0.2 wt.% < Fe < 0.65 wt.%, preferably 0.25 wt.% < Fe < 0.55 wt.% The iron content of 0.2 wt.% < Fe < 0.8 wt.% in combination with the manganese content according to the invention in the stated amount leads to the formation of Al6(Mn,Fe) phases and, as already explained above, in combination with the silicon and manganese contents according to the invention in the stated amounts, to the precipitation of particles of the quaternary a-Al(e,Mn)Si phase. Iron contributes to reducing the solubility of manganese in aluminum, whereby more manganese is bound in intermetallic phases, which has a positive effect on electrical and thermal conductivity.In addition, the intermetallic phases influence recovery and recrystallization processes and improve the thermal stability of the mechanical properties. Iron contents of more than 0.8 wt.% promote the formation of coarse intermetallic phases, which can impair formability in the deep-drawing process. Iron contents that are too low, less than 0.2 wt.%, on the other hand, severely restrict the tolerance of the aluminum alloy for ferrous scrap, since common scrap grades generally contain a significant iron content. Therefore, excessively restricting the iron content can hinder the realization of high recycling rates. The iron content range of the aforementioned embodiment of 0.2 wt.% < Fe < 0.65 wt.%, preferably 0.25 wt.% < Fe < 0.55 wt.%, therefore represents an ideal combination of recyclability, use of high recycled material content, thermal stability, electrical and thermal conductivity, and formability.

[0024] According to the invention, the copper content of the aluminum alloy is in the range Cu < 0.6 wt.%. In one embodiment of the battery cell housing according to the invention, the copper content of the aluminum alloy is in the range Cu < 0.3 wt.%, preferably 0.1 wt.% < Cu < 0.2 wt.%, particularly preferably 0.10 wt.% < Cu < 0.20 wt.%. By permitting a copper content of up to 0.6 wt.%, an increased tolerance of the aluminum alloy for copper-containing aluminum alloy scrap is achieved, which favors the realization of high recycled material proportions in the production of the battery housing. However, since excessive copper contents can have a negative effect on the corrosion properties, the copper content is limited according to the invention to a maximum of 0.6 wt.% in order to achieve sufficiently high electrolyte resistance.For improved electrolyte resistance and sufficiently high electrical and thermal conductivity, the copper content in the above-mentioned embodiment is limited to 0.3 wt.%. However, the presence of copper also simultaneously increases the strength of the aluminum alloy through solid solution strengthening, which, however, only becomes significantly apparent at a content of 0.1 wt.%. A preferred range of 0.1 wt.% < Cu < 0.2 wt.% or 0.10 wt.% < Cu < 0.20 wt.% thus represents a compromise between high strength, sufficiently high electrical and thermal conductivity, and further improved electrolyte resistance while maintaining sufficient recycling tolerance.

[0025] According to the invention, the manganese content of the aluminum alloy is in the range 0.3 wt% < Mn < 1.5 wt%. In one embodiment of the battery cell housing according to the invention, the manganese content of the aluminum alloy is in the range 0.3 wt% < Mn < 1.4 wt%. The manganese content of 0.4 wt.% < Mn < 1.3 wt.%, or 0.6 wt.% < Mn < 1.1 wt.%, in combination with the silicon and iron contents in the specified amounts, leads, as already explained above, to the precipitation of particles of the quaternary a-Al(Fe,Mn]Si phase and the Al(Mn,Fe] phase. The intermetallic phases hinder recovery and recrystallization processes and thus improve the thermal stability of the mechanical properties. Manganese contents of less than 0.3 wt.% result in only a very slight increase in strength through dispersoid and solid solution hardening, so that at least 0.3 wt.% manganese is required. From manganese contents of at least 0.4 wt.-%, significant increases in strength are achieved through dispersoid and solid solution hardening, which are even greater from at least 0.6 wt.% manganese. At manganese contents of more than 1.5 wt.%, the formation of coarse intermetallic phases is favored, which have an adverse effect on the forming properties in the deep drawing process. In addition, manganese contents of more than 1.5 wt.% reduce the electrical and thermal conductivity of the battery cell housing so much that thermal management becomes inefficient. The Mn content is therefore preferably a maximum of 1.5 wt.%, preferably a maximum of 1.3 wt.%, particularly preferably a maximum of 1.1 wt.%. According to a further embodiment, the Mn / Si ratio is preferably more than 0.8, since above this ratio the formation of a-Al(Te,Mn)Si phase is favored.

[0026] According to the invention, the magnesium content of the aluminum alloy is in the range 0.01 wt.% < Mg < 0.60 wt.%. In one embodiment of the battery cell housing according to the invention, the magnesium content of the aluminum alloy is in the range 0.05 wt.% < Mg < 0.55 wt.%, preferably 0.10 wt.% < Mg < 0.45 wt.%. By permitting a magnesium content of up to 0.60 wt.%, a tolerance of the aluminum alloy for magnesium-containing aluminum alloy scrap, such as packaging and UBC scrap, is achieved, which favors the realization of high recycling rates in the production of the battery cell housings. At the same time, limiting the Mg content to 0.60 wt.% allows for higher Si contents without the aluminum alloy being prone to hot cracking and weld pore formation. In addition, the presence of magnesium at a content of at least 0.01 wt.%, preferably at least 0.05 wt.%, particularly preferably more than 0.05 wt.-% or more preferably at least 0.10 wt.% to a solid solution strengthening, which contributes to increased work hardening and thus can provide higher strength. To achieve improved mechanical properties while simultaneously providing optimal process windows for welding processes, the magnesium content is limited to preferred ranges of 0.05 wt.% < Mg < 0.55 wt.%, preferably 0.05 wt.% < Mg < 0.50 wt.% or particularly preferably 0.10 wt.% < Mg < 0.45 wt.% and a compromise is achieved between high strength, good formability and high electrical and thermal conductivity with good recycling tolerance and weldability.

[0027] According to the invention, the chromium content of the aluminum alloy is in the range Cr < 0.25 wt.%. In one embodiment of the battery cell housing according to the invention, the chromium content of the aluminum alloy is in the range Cr < 0.1 wt.%, preferably Cr < 0.05 wt.%. By permitting a chromium content of up to 0.25 wt.%, the aluminum alloy achieves an increased tolerance for chromium-containing aluminum alloy scrap, which favors the realization of high recycling rates in the production of the battery cell housings. In addition, chromium also increases strength and forms dispersoids that increase thermal stability and inhibit softening due to recrystallization or recovery. However, since excessive chromium contents can have a negative effect on the electrical conductivity of the aluminum alloy, the chromium content is limited to a maximum of 0.25 wt.% according to the invention.For improved conductivity while still maintaining sufficient recycling tolerance and strength, the chromium content in the above-mentioned embodiment is limited to 0.1 wt.%, preferably 0.05 wt.%.

[0028] According to the invention, the zinc content of the aluminum alloy is in the range Zn < 0.5 wt.%. In one embodiment of the battery cell housing according to the invention, the zinc content of the aluminum alloy is in the range 0.02 wt.% < Zn < 0.30 wt.%, preferably 0.04 wt.% < Zn < 0.25 wt.%. By permitting a zinc content of up to 0.5 wt.%, an increased tolerance of the aluminum alloy for zinc-containing aluminum alloy scrap is achieved, which further promotes the realization of high recycling rates. In addition, zinc also has a strength-enhancing effect. However, since excessive zinc contents impair the weldability, electrical and thermal conductivity, and corrosion resistance of the aluminum alloy, the zinc content is limited according to the invention to a maximum of 0.5 wt.%. In the mentioned embodiment, the zinc content is within the corridor 0.02 wt% < Zn < 0.30 wt%, preferably 0.04 wt% < Zn < 0.25 wt%.-%, which achieves an optimal compromise between high strength, good weldability and good electrolyte resistance while still maintaining good recycling tolerance.

[0029] According to the invention, the titanium content of the aluminum alloy is in the range Ti < 0.2 wt.%. In one embodiment of the battery cell housing according to the invention, the titanium content of the aluminum alloy is in the range 0.005 wt.% < Ti < 0.1 wt.%, preferably 0.005 wt.% < Ti < 0.05 wt.%. By permitting a titanium content of up to 0.2 wt.%, an increased tolerance of the aluminum alloy for titanium-containing aluminum alloy scrap is achieved, which favors the realization of high recycling rates in the production of battery cell housings. However, excessively high titanium contents can negatively influence the forming properties of the aluminum alloy and significantly reduce the electrical and thermal conductivity, so that the titanium content is limited according to the invention to a maximum of 0.2 wt.%. In contrast, titanium at a content of 0.005 wt.% and above improves grain refinement during casting of the aluminum alloy.For good grain refinement combined with good formability, sufficiently high electrical and thermal conductivity and sufficient recycling tolerance, the titanium content in the embodiment mentioned is therefore set within the corridor 0.005 wt% < Ti < 0.1 wt%, preferably 0.005 wt% < Ti < 0.05 wt%.

[0030] In addition to the alloying constituents mentioned above, the aluminum alloy of the battery cell housing according to the invention contains aluminum and unavoidable impurities as the remainder. Unavoidable impurities are alloying constituents that are not intentionally added to the alloy, but are inevitably present in the aluminum alloy due to the manufacturing process. According to the invention, the content of a single unavoidable impurity is limited to 0.05 wt.%, and the total content of all unavoidable impurities is limited to 0.15 wt.%. This ensures that the unavoidable impurities have no, or no significant, negative effects on the properties of the aluminum alloy, for example, through undesirable phase formation.

[0031] In a further embodiment of the battery cell housing according to the invention, the aluminum alloy has a proportion of at least 50 wt. %, preferably at least 70 wt. %, particularly preferably at least 85 wt. % recycled material. Due to the above-described high recycling tolerance of the aluminum alloy, the realization of these high recycled contents for the battery cell housing according to the invention is made possible without negatively affecting the process parameters for preferred manufacturing processes, such as the welding process. The associated energy savings enable the production of battery cell housings with the smallest possible Ct footprint and achieve improved sustainability. The recycled material of the battery cell housing preferably has a proportion of at least 50 wt. %, preferably at least 70 wt. %, particularly preferably at least 85 wt. % post-consumer scrap.Since post-consumer scrap only arises at the end of the product life cycle, it is considered particularly sustainable and contributes to reducing the carbon footprint. Cumulatively or alternatively, the recycled material contains at least 50 wt.%, preferably at least 70 wt.%, particularly preferably at least 85 wt.% pre-consumer scrap, or internal and / or external process scrap. In the case of internal process scrap, the compositions and quantities of the individual alloys are generally very well known, so that the alloy composition resulting from the melting of internal process scrap can be easily determined. The composition of external process scrap is less well-defined than internal process scrap and may require further processing steps. However, it is generated in large quantities, for example, in the production of stamped parts, making recycling highly relevant both economically and in terms of sustainability.By recycling external process scrap, the demand for primary metal can be reduced, thus lowering the overall carbon dioxide (CH) balance. Although the exemplary embodiments described below have a maximum recycling content of 85%, recycling contents of at least 90% are also achievable with the aluminum alloy composition according to the invention.

[0032] In a further embodiment of the battery cell housing according to the invention, the aluminum alloy strip or sheet has a cold-worked state of type HIX or a reannealed state of type H2x. In particular, these are the states H12, H14, H16, H18, and H19 familiar to those skilled in the art. Preferably, the aluminum alloy strip or sheet has the cold-worked state H18 or H19. These states, in particular H18 and H19, are characterized by particularly high mechanical stability, so that particularly high strengths can be provided for the battery cell housing. Reannealed states of type H2x have improved forming potential and are often very thermally stable, making them ideal for battery cell housings.

[0033] If the aluminum alloy strip or sheet according to a further embodiment of the battery cell housing has a thickness between 0.1 mm and 2.0 mm, the wall thicknesses typical for a battery cell housing can be completely covered. Reducing the thickness to less than 0.1 mm reduces the mechanical stability of the battery cell housing too much. In contrast, with a thickness of more than 2.0 mm, efficient use of materials is no longer possible. In addition, the gravimetric and volumetric energy density of the battery cell or battery module or battery system would be reduced too much if the aluminum alloy strip or sheet of the battery cell housing had a thickness of more than 2.0 mm. The thickness of the aluminum alloy strip or sheet is preferably between 0.25 mm and 1.5 mm, in particular between 0.35 mm and 1.2 mm.

[0034] In a further embodiment of the battery cell housing according to the invention, the aluminum alloy strip or sheet has an electrical conductivity er of at least 40% 1ACS. Compared to the battery cell housings made of nickel-plated steel previously used for cylindrical cells, the electrical conductivity is thus significantly increased, resulting in faster charging times, lower electrical losses, and thus less heat generation during battery cell operation. Due to the Wiedemann-Franz law, which states that there is a direct relationship between the electrical and thermal conductivity of a metal, the increased electrical conductivity is also accompanied by increased thermal conductivity compared to nickel-plated steel. This allows the waste heat generated during battery cell operation to be dissipated more efficiently, which, among other things, improves the battery's fast-charging capability.Furthermore, the higher thermal conductivity leads to a more homogeneous temperature distribution within the cell, which has a positive effect on its aging. The electrical conductivity of at least 40% 1ACS thus leads to overall improved battery cell performance. Compared to alloy AA3003, which represents the standard for prismatic battery cell casings and typically has a conductivity between 39.5% 1ACS and 50% 1ACS, this inventive electrical conductivity is comparable, so no significant changes or even impairments to the thermal or electrical properties of the prismatic battery cell are to be expected through the use of inventive materials with a high recycled content.

[0035] In a further embodiment, the aluminum alloy strip or sheet has a yield strength R Po,2 of at least 125 MPa, preferably at least 150 MPa, in particular at least 180 MPa. This makes it possible to provide high strengths for the battery cell housing, which reach the minimum strength of the standard for prismatic battery cans AA3003 H14 and preferably significantly exceed it, so that the wall thicknesses of the cell housing can at least be maintained, but preferably reduced. For cylindrical battery cell housings with steel as the reference material, the above-mentioned higher yield strength values ​​allow the necessary increase in wall thickness to be moderate and the overall capacity of the battery cell to be only slightly affected by the reduced internal volume. The aluminum alloy strip or sheet preferably has the stated values ​​for the yield strength before it is processed into the battery cell housing, for example in the H14, H18 or H24 temper.Since the processing of the aluminum alloy strip or sheet, which typically involves cold forming such as deep drawing, is generally accompanied by an increase in strength, it can be assumed that the specified minimum yield strength values ​​also apply to the battery cell housing according to the invention in its finished state. Even with alternative manufacturing processes for prismatic battery cell housings based on local cold forming, such as roll forming, consistent or improved strength can be expected compared to the AA3003 alloys used previously.

[0036] In a further embodiment of the battery cell housing according to the invention, the aluminum alloy strip or sheet, prior to its processing into the battery cell housing, has a wall thickness ratio θ with respect to steel of at most 2.8, preferably at most 1.95. The wall thickness ratio θ with respect to steel is determined by determining the yield strength R P o,2,st of a nickel-plated steel strip of type A1S11020 by the yield strength R P O,2,AI of the aluminum alloy strip, where R P o,2,st, a typical value of 350 MPa is assumed. To derive the wall thickness ratio 8, the practical scenario of internal pressure loading for battery cell casings is considered. For simplification, the battery cell casing is assumed to be a closed, thin-walled cylinder.

[0037] Based on this, the calculation of the wall thickness ratio 8 in relation to steel is carried out using the boiler formula known from elastostatics with c : stress component in circumferential direction, p: internal pressure, Rj inner radius, s: wall thickness

[0038] Using the equivalent stress according to Tresca V, Tresca and taking into account a design against a load limited by the onset of flow with V, Tresca — ^p0,2 [3]

[0039] Assuming the same maximum internal pressure with the same inner radii R t of the cells: so that the wall thickness ratio 8 can be calculated from the yield strength ratio mentioned:

[0040] The wall thickness ratio θ relative to steel is a measure of the increase in the wall thickness of the battery cell housing when steel is replaced by aluminum and can be used, in particular, to compare different aluminum alloy strips or sheets. The θ value according to the invention of at most 2.8, preferably at most 1.95, also has a positive effect on the gravimetric energy density of the battery cells, since, in conjunction with the low density of aluminum compared to steel, the gravimetric energy density can be significantly increased in some cases.

[0041] The inventive values ​​of the yield strengths R P o2 are above, preferably significantly above, the values ​​for the yield strength R Po2 of the standard material for prismatic cell casings, AA3003 H14, so that common wall thicknesses can be maintained or reduced. The preferred higher-strength version, in particular, enables reduced wall thicknesses, which increases the gravimetric and volumetric energy density of prismatic batteries.

[0042] According to a second teaching of the present invention, the above-mentioned object for the use of an aluminum alloy strip or sheet for producing a battery cell housing is achieved by using the aluminum alloy strip or sheet for producing a battery cell housing according to the first teaching of the invention. Due to the already stated advantageous properties of the aluminum alloy strip or sheet, a battery cell housing that is improved compared to the prior art can thus be provided.

[0043] In one embodiment of the use according to the invention, the battery cell housing is a housing for a secondary cell, preferably a lithium-ion secondary cell or a sodium-ion secondary cell. Since secondary cells, in particular lithium-ion secondary cells, are currently increasingly used in the fields of electromobility and consumer electronics, the advantageous properties of the aluminum alloy strip or sheet used according to the invention can be exploited particularly for this type of battery cell. This also applies to sodium-ion secondary cells, which are currently still primarily the subject of research or are finding initial industrial application and could replace lithium-ion secondary cells in certain applications in the future due to their improved cost-effectiveness and the readily available sodium.The use of the battery cell housing according to the invention furthermore includes in particular the use of the housing for solid-state secondary cells which have a solid-state electrolyte.

[0044] In a further embodiment of the use according to the invention, the battery cell housing has a cylindrical design, a prismatic design, or a pouch design. This allows the advantageous properties of the aluminum alloy strip or sheet used according to the invention to be utilized in all currently common battery cell housing designs.

[0045] In a further embodiment of the use according to the invention, the aluminum alloy strip or sheet is produced by a process comprising the following steps:

[0046] Casting a rolling ingot made of an aluminum alloy, homogenizing the rolling ingot, hot rolling the rolling ingot into a hot-rolled strip, cold rolling the hot-rolled strip with optional intermediate annealing and optional temper annealing of the cold-rolled strip, preferably re-annealing of the cold-rolled strip.

[0047] The aforementioned process steps are preferably carried out in the specified order, whereby the homogenization of the rolling ingot can be carried out separately or integrated into the preheating of the rolling ingot for hot rolling. It has been found that the process just described can be used to produce an aluminum alloy strip or sheet which, when used according to the invention, meets the requirements for a battery cell housing, particularly with regard to strength, electrolyte resistance, and electrical and thermal conductivity with excellent weldability, while simultaneously achieving high recycling rates. Furthermore, this process allows for economical production of the aluminum alloy strip or sheet.

[0048] The rolling ingot from an aluminum alloy is preferably cast using direct cooling continuous casting, also known as direct chill continuous casting or DC continuous casting, which further increases the economic efficiency of the manufacturing process.

[0049] Homogenizing the rolled ingot improves the microstructure of the aluminum alloy strip or sheet, which has a positive effect on strength and formability. Homogenization preferably takes place at a temperature of 480°C to 620°C, in particular 550°C to 610°C, for a duration of at least 0.5 h, preferably at least 1 h, in particular at least 2 h.

[0050] The hot rolling of the rolling ingot to form a hot-rolled strip preferably takes place at a temperature between 280 °C and 550 °C, with the hot strip temperature after the last hot rolling pass being between 280 °C and 380 °C, preferably between 310 °C and 360 °C. The hot rolling of the rolling ingot can take place either reversibly on a rolling stand or sequentially in a tandem stand. In particular, hot rolling can take place reversibly up to a blank thickness of between 20 mm and 50 mm and the blank can then be rolled to hot strip thickness in a tandem stand. The hot strip thickness, i.e. the thickness of the hot-rolled strip, in one embodiment of the process is between 1 mm and 15 mm, preferably between 2 mm and 12 mm, in particular between 2 mm and 9 mm.In this way, it is ensured that a sufficiently high degree of rolling can be achieved during the subsequent cold rolling, which determines the strength and formability as well as the crystallographic texture and thus the ear profile of the aluminum alloy strip or sheet.

[0051] The cold rolling of the aluminum alloy strip or sheet can be carried out in one or more passes. In one embodiment of the process in which several cold rolling passes are carried out, at least one intermediate annealing step is optionally carried out during cold rolling. In one embodiment of the process, the intermediate annealing step takes place in the temperature range between 150°C and 450°C, preferably between 200°C and 400°C, in particular between 300°C and 400°C. The intermediate annealing step is preferably carried out as a recrystallization annealing step, which provides a recrystallized microstructure for the subsequent cold rolling step. This cold rolling step can then be carried out with a higher degree of rolling reduction, which has a strength-enhancing effect on the finish-rolled aluminum alloy strip or sheet. Alternatively, instead of a recrystallization annealing step, a recovery annealing step can be carried out, which reduces hardening.All temperatures mentioned which characterise annealing processes always refer to peak metal temperatures (PMTJ), i.e. the highest temperatures of the metal in the annealing furnace.

[0052] In one embodiment of the process, the degree of reduction during cold rolling to final thickness is at least 20%, preferably at least 50%, in particular at least 70%. If the process is carried out with intermediate annealing during cold rolling, the degree of reduction in cold rolling to final thickness after the last intermediate annealing is at least 20%, preferably at least 50%, in particular at least 70%. The degree of reduction during cold rolling to final thickness of at least 20%, preferably at least 50%, in particular at least 70%, can increase the strength of the produced aluminum alloy strip or sheet, making it particularly suitable for the use according to the invention.

[0053] Optional temper annealing allows for the provision of an aluminum alloy strip that is tailored to the battery housing manufacturing process, particularly to forming processes, while simultaneously exhibiting maximum electrical and thus thermal conductivity values. This is achieved through the precipitation of dissolved alloy components during temper annealing. Battery cell housings are preferably manufactured from aluminum alloy strips in the as-rolled Hix or H2x temper annealed states. However, soft-annealed versions are at least conceivable for very low strength requirements of the battery cell housing in combination with a high-strength material.

[0054] The invention will be explained in more detail below using exemplary embodiments, with reference also to the drawing. The drawing shows in Fig. 1 a schematic representation of a battery cell of cylindrical design with a battery cell housing according to the invention,

[0055] Fig. 2 is a schematic representation of a battery cell of prismatic design with a battery cell housing according to the invention,

[0056] Fig. 3 is a schematic representation of a battery cell in pouch design with a battery cell housing according to the invention, and

[0057] Fig. 4 is a flow chart of a process for producing an aluminum alloy strip or sheet for use in the present invention.

[0058] Fig. 1 shows a schematic representation of an embodiment of a cylindrical battery cell 10. The battery cell 10 has a battery cell housing 11 according to the invention, as well as an anode terminal 12 and a cathode terminal 13.

[0059] Fig. 2 shows a schematic representation of an embodiment of a prismatic battery cell 20. The battery cell 20 has a battery cell housing 21 according to the invention, as well as an anode terminal 22 and a cathode terminal 23.

[0060] Fig. 3 shows a schematic representation of an embodiment of a pouch-type battery cell 30. The battery cell 30 has a battery cell housing 31 according to the invention, as well as an anode terminal 32 and a cathode terminal 33. Fig. 4 shows a flowchart of an embodiment of a method 40 for producing an aluminum alloy strip or sheet for use according to the invention. The method 40 comprises the following steps:

[0061] Casting (42) of a rolling ingot made of an aluminum alloy, homogenizing (44) the rolling ingot, hot rolling (46) of the rolling ingot to a hot-rolled strip, cold rolling (48) of the hot-rolled strip with optional intermediate annealing and optional final annealing (both not shown).

[0062] After cold rolling, the strips are in the H12, H14, H16, H18, or H19 states, depending on the cold rolling grade of the hot strip thickness or the intermediate annealing thickness. However, cold rolling can optionally be followed by a heat treatment (not shown) of the strip in the form of a temper annealing, preferably in the form of reannealing. After reannealing, the values ​​for the yield strength R P o.2 is hardly reduced. However, the possible degrees of deformation and conductivities are improved, for example, in the H24 temper. This is demonstrated by the following examples. It is also conceivable to produce the aluminum strips using manufacturing processes that involve continuous casting of the aluminum strip. In this case, steps 42, 44, and 46 are omitted, and the resulting cast strip is cold-rolled.

[0063] A total of 10 different aluminum alloy strips were produced, with the chemical composition of aluminum alloys 2 to 9 having recycling contents of more than 50%. The respective alloy compositions of strips 1 to 10 are given in Table 1 below. The contents of the individual alloying elements are all given in wt.%. The remainder, i.e. the difference to 100 wt.%, consists of aluminum and unavoidable impurities, individually a maximum of 0.05 wt.%, in total a maximum of 0.15 wt.%. Strips 2 to 8 represent aluminum alloy strips according to the invention which allow for very high recycling contents. As examples, strips 2, 3 and 4 were produced with 77%, 74% and 86% recycling contents, respectively, with the recycling content including both internal scrap, so-called pre-consumer scrap, and external scrap. Aluminum alloy strip 9 was produced with 90% recycled content, but has excessive magnesium content.In contrast, Comparative Example 10, which has a magnesium-free composition, requires primary aluminum-based production of the aluminum alloy without recycled content.

[0064] Aluminum alloy strips 1 to 10 were produced using the process shown in Fig. 4. The different tempering states are listed in Table 2. Specifically, rolling ingots were cast from the respective aluminum alloys using the DC continuous casting process. A proportion of at least 70 wt.% recycled material was selected for the production of the rolling ingots of the inventive strips 2 to 8. Comparative Example 10 was cast from primary aluminum based on ingots and master alloys.

[0065] Table 1 The rolling ingots were homogenized after casting and subsequently hot-rolled into strips. The hot-rolled strips were then cold-rolled to a final thickness of between 0.47 mm and 1.5 mm. Strips 2, 3, 4, 6, and 8 according to the invention, as well as Comparative Example 10, are in the as-rolled conditions H14 and H18 after cold rolling. The intermediate annealings were carried out by coil annealing at 320 °C PMT. Example 1 was soft-annealed to the O condition after cold rolling. A coil annealing was also carried out during this process. The holding time for the coil annealing after the heating phase was at least 3 hours at the specified PMT for all coil annealings.

[0066] Examples 5 and 7, as well as Comparative Example 9, were brought to the H24 temper by reannealing. For laboratory annealing, sheet sections were annealed, for example, at a PMT of 240°C in a laboratory furnace for 3 hours. Finally, aluminum alloy strips 6, 7, and 8 were produced from an identical alloy with different final thicknesses and tempering states, here H18 and H24. As expected, the tempering states determine the values ​​for the yield strength R almost independently of the final thickness. P o,2.

[0067] The following Table 2 shows various process parameters for the production of strips 1 to 10. Specifically, these are the hot strip thickness, i.e., the respective thickness of the hot-rolled strip, the temperature of the intermediate and final annealing as PMT, the cold rolling grade starting from the hot strip if no intermediate annealing was planned, or starting from the thickness of the aluminum strip after intermediate annealing up to the final thickness of the aluminum strip. Table 2 also shows the proportion of recycled metal. This proportion results from the mass of the sum of the internal scrap used, i.e., scrap from the production of aluminum strip or sheet, and the external scrap used, which consists of post-consumer and further processing scrap, in relation to the mass of the primary metal used in the production of the respective exemplary embodiment. e 2

[0068] As can be seen from Table 2, strip no. 1 (comparative example) was produced without intermediate annealing and brought to the 0-tempered state by a final soft annealing. Strips 2 to 4 according to the invention and the comparative example strip no. 10 were produced with intermediate annealing of the respective coils in a corresponding coil furnace. Strips 5 to 9 were rolled to their final thickness without intermediate annealing, like strip no. 1. Strips 5, 7, and 9 were brought to the semi-hard H24 temper by a final annealing, while strips 6 and 8 were not annealed and were tested in the as-rolled H18 temper. As already explained, the specified annealing temperatures (PMT) of the metal were maintained for at least 3 hours during all coil annealing processes.

[0069] The aluminum alloy strips were then tested for various properties relevant to battery cell casings. The results of these tests are summarized in Table 3. The focus was on the yield strength R P o.2, the electrical conductivity in %1ACS and the weldability.

[0070] All aluminum alloy strips according to the invention demonstrated sufficiently large (+) process windows in terms of weldability, enabling reliable sealing of battery cell housings. Comparative Example 10, due to its strictly limited chemical composition, enables an even larger process window (+). However, due to the severely restricted chemical composition, the use of scrap, particularly external scrap, preferably external post-consumer scrap, is very limited compared to the strips according to the invention. Comparative Example 9, with a significantly higher Mg content, demonstrated a narrower process window in the welding tests due to an increased tendency to hot cracking and a greater tendency to pore formation, with a negative impact on the seal, which entails the risk of a higher scrap rate. The values ​​for the yield strength R Po,2 were determined in tensile tests according to DIN EN ISO 6892-1 and showed values ​​of at least 183 MPa for the inventive examples. The wall thickness ratio 8 in relation to steel was determined by determining the yield strength R P o,2,st of 350 MPa, which is a typical value for a nickel-plated steel strip of type AISI1020, by the yield strength R P O,2,AI of the respective aluminum alloy strip.

[0071] Table 3

[0072] The inventive embodiments with work-hardened HIX condition, particularly in H18 condition, allow the use of wall thickness ratios in the range of 1.24 to 1.32. Thus, a high gravimetric energy density of the battery cells can be expected. Slightly reduced gravimetric energy densities can be achieved due to the lower yield strength R P o,2 with reannealed

[0073] Variants in the H24 temper are expected. However, these in turn result in significant advantages in electrical conductivity and thus also in thermal conductivity of almost 3%. For application in prismatic battery cells, whose battery cell casings are usually made of alloy AA3003 in the H14 temper, yield strengths R P o2 more than 125MPa in order to be able to maintain or even reduce the wall thickness of common cell formats, for example at yield strengths.

[0074] The electrical conductivities in %1ACS of the exemplary embodiments according to the invention are consistently between approximately 5.5% and a maximum of approximately 25% higher than in comparative example 9, which also has a high recycling content, so that the thermal management of the battery cell housings made of aluminum alloy strips according to the invention is likely to be significantly improved compared to this comparative example.

[0075] With electrical conductivities of at least 44% 1ACS and more, the electrical conductivity is significantly increased compared to the previously used battery cell casings of round cells made of nickel-plated steel, so that faster charging times, lower electrical losses and thus also less heat generation during operation of the battery cells can be achieved.

[0076] The electrical conductivities of the strips according to the invention are also comparable to the standard material for prismatic battery cell casings, AA3003 H 14, which is represented by Comparative Example 10. Due to the Wiedemann-Franz law, which states that there is a direct relationship between electrical and thermal conductivity in metals, analogous considerations also apply to thermal conductivity. The improved thermal conductivity of the aluminum alloy strips according to the invention compared to nickel-plated steel enables significantly more efficient cooling of the battery cells, particularly at the high C-rates encountered during rapid charging. At the same time, a more homogeneous temperature distribution is expected due to the improved thermal conductivity across the winding, thereby improving the aging properties of the battery cell.As Table 3 further shows, the strips according to the invention have a thickness between 0.1 mm and 2.0 mm. This achieves a good compromise between mechanical stability and efficient material use when used to manufacture a battery cell housing according to the invention.

[0077] The battery cells (10, 20, 30) shown in Figs. 1 to 3 can be secondary cells, in particular lithium-ion secondary cells or sodium-ion secondary cells, so that the battery cell housings (11, 21, 31) according to the invention are accordingly each housing of a secondary cell, in particular a lithium-ion secondary cell or a sodium-ion secondary cell. Thus, the advantageous properties of the aluminum alloy strips used according to the invention can be utilized, particularly for these types of battery cells.

[0078] Furthermore, the battery cell housings (11, 21, 31) according to the invention shown in Figs. 1 to 3 can, in particular, have a cylindrical design, a prismatic design, or a pouch design. Fig. 1 shows a battery cell housing (11) according to the invention in a cylindrical design; Fig. 2 shows a battery cell housing (21) according to the invention in a prismatic design; and Fig. 3 shows a battery cell housing (31) according to the invention in a pouch design. Thus, the advantageous properties of the aluminum alloy strips used according to the invention can be utilized in all currently typical battery cell housing designs.

[0079] Furthermore, the aluminum alloys underlying the battery cell housings (11, 21, 31) according to the invention shown in Figures 1 to 3 preferably have a proportion of at least 50 wt. %, preferably at least 70 wt. %, or particularly preferably at least 85% recycled material. The recycled content is preferably achieved by using post-consumer scrap. The associated energy savings enable the production of battery cell housings with the smallest possible Ct footprint and increase the sustainability of the battery cell housings. The high recyclability of the battery cell housing (11, 21, 31) according to the invention is in turn due to its alloy composition, which allows high recycled content, preferably of post-consumer scrap.Additionally or alternatively, the recycling share can also be achieved by using internal or external process scrap and also a reduction of the Ct footprint compared to primary aluminum-based production can be achieved.

Claims

Patent claims 1. Battery cell housing (11, 21, 31) comprising an aluminum alloy strip or sheet, characterized in that the aluminum alloy strip or sheet comprises an aluminum alloy with the following alloying constituents in wt.%: 0.1% < Si < 0.7%, 0.2% < Fe < 0.8%, Cu < 0.6%, 0.3% < Mn < 1.5%, 0.01% < Mg < 0.60%, preferably 0.05% < Mg < 0.55%, Cr < 0.25%, Zn < 0.5%, Ti < 0.2%, Remainder Al and unavoidable impurities, individually maximum 0.05%, in total maximum 0.15%.

2. Battery cell housing according to claim 1, characterized in that the aluminum alloy strip or sheet comprises an aluminum alloy with the following alloying constituents in wt.%: 0.2% < Si < 0.55%, preferably 0.35% < Si < 0.55%, 0.2% < Fe < 0.65%, preferably 0.25% < Fe < 0.55%, Cu < 0.3%, preferably 0.1% < Cu < 0.2%, 0.3% < Mn < 1.3%, preferably 0.4% < Mn < 1.1%, 0.05% < Mg < 0.50%, preferably 0.10% < Mg < 0.45%, Cr < 0.1%, preferably Cr < 0.05%, 0.02% < Zn < 0.30%, preferably 0.04% < Zn < 0.25%, 0.005% < Ti < 0.1%, preferably 0.005% < Ti < 0.05%, Remainder Al and unavoidable impurities, individually maximum 0.05%, in total maximum 0.15%.

3. Battery cell housing according to claim 1 or 2, characterized in that the aluminum alloy has a proportion of at least 50 wt.%, preferably at least 70 wt.%, particularly preferably at least 85 wt.% recycled material.

4. Battery cell housing according to one of claims 1 to 3, characterized in that the aluminum alloy strip or sheet has a work-hardened state of the HIX type, preferably the work-hardened state H18 or H19 or a reannealed state H2x, preferably H24.

5. Battery cell housing according to one of claims 1 to 4, characterized in that the aluminum alloy strip or sheet has a thickness between 0.1 mm and 2.0 mm, preferably between 0.25 mm and 1.5 mm, particularly preferably between 0.35 mm and 1.2 mm.

6. Battery cell housing according to one of claims 1 to 5, characterized in that the aluminum alloy strip or sheet has an electrical conductivity of at least 40% 1ACS.

7. Battery cell housing according to one of claims 1 to 6, characterized in that the aluminum alloy strip or sheet, preferably before its Processing into the battery cell housing, a yield strength R P o,2 of at least 125 MPa, preferably at least 150 MPa, particularly preferably at least 180 MPa.

8. Use of an aluminum alloy strip or sheet for producing a battery cell housing according to one of claims 1 to 7.

9. Use according to claim 8, characterized in that the battery cell housing is a housing of a secondary cell, preferably a lithium-ion secondary cell, a sodium-ion secondary cell or a solid-state secondary cell.

10. Use according to claim 8 or 9, characterized in that the battery cell housing has a cylindrical design, a prismatic design or a pouch design.

11. Use according to one of claims 8 to 10, characterized in that the aluminum alloy strip or sheet is produced by a process (40) comprising the following steps: Casting (42) a rolling ingot made of an aluminum alloy, homogenizing (44) the rolling ingot, Hot rolling (46) of the rolling ingot to a hot-rolled strip, cold rolling (48) of the hot-rolled strip and, optionally, annealing the cold-rolled strip, preferably re-annealing the cold-rolled strip.

12. Use according to claim 11, characterized in that The thickness of the hot-rolled strip is between 1 mm and 15 mm, preferably between 2 mm and 12 mm, particularly preferably between 2 mm and 9 mm.

13. Use according to claim 11 or 12, characterized in that at least one intermediate annealing takes place during cold rolling.

14. Use according to one of claims 11 to 13, characterized in that the degree of rolling during cold rolling to final thickness, preferably the degree of rolling after the last intermediate annealing, is at least 20%, preferably at least 50%, particularly preferably at least 70%.

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