Aluminum alloys as anodes for aluminum battery production

Abstract

The present invention relates to aluminum alloys for making anodes for use in the manufacture of batteries.

Description

[Technical Field]

[0001] A battery, also called an electrochemical cell or simply a cell, is a device that can convert chemical energy directly into electrical energy during the discharge phase.

[0002] A battery always consists of at least two electrodes: 1) an anode (negative electrode [-]), 2) a cathode (positive electrode [+]), and an electrolyte.

[0003] An "anode + electrolyte" or "cathode + electrolyte" pair is called an anode half-cell or a cathode half-cell, respectively.

[0004] During battery discharge, at least the following events occur in the anode half-cell: 1) oxidation of the anode material and the resulting loss of electron current from the half-cell; and 2) the migration of ions from the anode to the cathode through the electrolyte.

[0005] Similarly, in the cathode half-cell, electrons flowing into a circuit external to the cell are utilized in the reduction reactions necessary to maintain a neutral charge balance.

[0006] It is therefore clear that the electrolyte serves to physically separate the anode and cathode and to ensure sufficient ionic conductivity between them; indeed, if the anode and cathode were to come into electrical contact, a short circuit would occur that would cancel the cell potential.

[0007] In developing a new battery, it is common to first develop each material (anode, cathode, and electrolyte) separately, then optimize the anode and cathode half-cells, and then the anode-electrolyte and cathode-electrolyte combinations, and finally develop the complete cell.

[0008] Recent advances in portable electronic devices and automotive applications have necessitated the development of high-performance energy storage systems that offer improved energy density, low-temperature performance, and high power output.

[0009] Today, lithium batteries cover almost the entire portable electronics market and are also showing great promise in automotive applications.

[0010] However, lithium does not fully meet the requirements in terms of safety, natural abundance, cost, and toxicity. In particular, lithium-ion batteries combine unfavorable factors, such as flammable electrolytes, toxic salts (which release hydrofluoric acid when exposed to moisture), and cobalt- and nickel-based cathodes, which have several drawbacks, including high toxicity.

[0011] Furthermore, lithium is not an abundant element (less than 0.01% of the Earth's crust) and its deposits are concentrated in just a few countries.

[0012] This has raised significant concerns about the element's future supply capacity, with prices increasing by more than 20% per year since 2015, for example.

[0013] Similar considerations can be made about the cost and carbon footprint of the nickel and cobalt used in the production of the most commonly used cathode materials (e.g., NMC, lithium nickel cobalt manganese oxide).

[0014] Specifically, the break-even point between electric vehicles powered by lithium-ion batteries and those powered by internal combustion engines is currently unclear, especially when the carbon footprint required to extract and process the raw materials is also taken into account.

[0015] As a result, batteries based on alternative metals have been investigated in recent years.

[0016] For example, sodium-, magnesium-, and aluminum-based devices offer inherent advantages over competing lithium-based technologies.

[0017] In particular, magnesium and aluminum are highly abundant elements in the Earth's crust (2.1% and 8.1% by weight, respectively), and therefore are inexpensive and pose few safety issues in their use, disposal, and waste management.

[0018] Furthermore, magnesium and aluminum have higher capacities per volume than lithium (3832, 8043, and 2062 mAh / cm for Mg, Al, and Li, respectively). 3 ).

[0019] Referring to FIG. 1, a typical aluminum battery consists of: a) an anode made of metallic aluminum foil; b) a liquid electrolyte made of, for example, a chloroaluminate-based ionic liquid (1-ethyl-3-methylimidazolium chloride) to which aluminum chloride (AlCl) has been added in an appropriate molar ratio; and c) a cathode based on a graphite material.

[0020] However, aluminum batteries mainly contain aluminum ions (valence 3 + Due to the high charge density of ZnO, it has the following drawbacks: a) its reactivity is limited, which inhibits reactions at the electrode (e.g., intercalation / deintercalation rate), and b) it reduces the conductivity of the electrode and electrolyte.

[0021] Furthermore, aluminum's high chemical affinity for oxygen and its consequent tendency to oxidize can lead to the formation of an oxide layer on the anode, causing passivation and reducing the plating / stripping ability of aluminum ions.

[0022] From an electrochemical point of view, pure aluminum has good properties as an anode, but it is known that a) it is particularly susceptible to corrosion phenomena that reduce stability during charge / discharge cycles; b) it has low coulombic efficiency and practical capacity; c) it is slow to react; and d) it is particularly susceptible to dendrite growth after plating / stripping cycles.

[0023] Chinese Patent No. 108642327 (Institute of Materials & Processing Guangdong Academy of Sciences) describes a material for manufacturing the anode of an aluminum-air cell, which contains, in addition to aluminum, gallium, lead, bismuth, iron, titanium (0.005-0.015%), boron (0.001-0.003% by weight) and less than 0.003% silicon.

[0024] Swiss Patents Nos. 679438 and 679437 (Alusuisse Lonza Group, Paul Scherrer Institute) describe batteries with anodes made of aluminum or aluminum alloys and one or more other elements, including lithium, magnesium, silicon, titanium and boron, and manufactured using a strongly acidic electrolyte.

[0025] The aluminum / air battery is a technology that uses an aqueous electrolyte and a non-solid cathode (e.g., air, oxygen). The reversibility, coulombic efficiency, operating voltage, capacity fade, shelf life, and the behavior of Al in the aqueous electrolyte are important. 3+ There is a major problem with the lack of ion transport.

[0026] WO 2018 / 090097 (Newsouth Innovations Pty Limited) describes an electrochemical cell for producing a battery in which the anode is made of aluminum or an aluminum / lithium alloy, the cathode is made of sulfur, and the electrolyte contains lithium ions.

[0027] WO 2022 / 055968 (Everon24, Inc.) describes the formation of a surface layer in the form of a coating (approximately 100 μm thick) of material (usually an oxide) on the surface of the anode or cathode of an aluminum battery in order to improve ion transfer ability or to suppress the formation of by-products at the interface between the anode and the electrolyte.

[0028] US Patent Application Publication No. 2004 / 0170523 describes a metal alloy of the general formula AlTi1-2B1-2 for die casting automotive safety parts; the alloy is characterized by specific mechanical properties, including high elongation in the as-cast state.

[0029] US Patent Application Publication No. 2012 / 0134874 describes metal alloys of the general formula AlSi5-13Ti1-3B1-3 for use in the automotive industry, which have a particular elasticity compared to alloys without titanium and boron additions.

[0030] US Patent Application Publication No. 2013 / 0136651 describes a metal alloy of the formula AlSi5-13Ti2-7B1-3 that has improved elastic properties and is suitable for high pressure forming.

[0031] Therefore, there is currently a need to develop an aluminum-based anode that does not have the above drawbacks. Summary of the Invention

[0032] The inventors have surprisingly found that aluminum alloys of the general formula AlSiXTiYBZ can be used to manufacture anodes for aluminum (Al) batteries.

[0033] The alloys can be used to provide highly efficient, reactive and reversible anodes for producing high performance batteries.

[0034] Object of the invention Therefore, in a first objective, aluminum alloys obtained by a particular method are described.

[0035] In a second objective, a method for manufacturing the aluminum alloy of the present invention is described.

[0036] The aluminum alloy itself is a particular aspect of the present invention.

[0037] In a third object, anodes made from the aluminum alloys of the present invention and batteries containing the anodes are described. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1 shows a schematic of a battery, with particular attention to the charge transfer that occurs during discharge. [Figure 2] Figure 2 is a graph showing the results of aluminum plating / stripping measurements obtained using the alloys of this application as working electrodes, with the measurements of a pure aluminum electrode and an EN-43200 alloy electrode shown in boxes as references. [Figure 3] Figure 3 shows an image of the metallographic analysis of the AlSi7Ti8B4 alloy. [Figure 4] FIG. 4 shows the constant current charge / discharge profile in the performance test. DETAILED DESCRIPTION OF THE INVENTION

[0039] Detailed Description of the Invention In a first object of the present invention, an aluminum alloy is provided.

[0040] In particular, the alloy contains at least 75% by weight of aluminum.

[0041] Furthermore, in addition to aluminum, the alloy contains boron and, in some cases, silicon and / or titanium.

[0042] For purposes of the present invention, the alloy has the following formula: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 0≦X≦10, 0≦Y≦10, and 2≦Z≦5.) It has.

[0043] In a more preferred aspect of the invention, the formula of the described alloy is: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 5≦X≦10, 0≦Y≦10, and 2≦Z≦5.) is.

[0044] In an even more preferred aspect of the present invention, the formula of the described alloy is: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 5≦X≦10, 4≦Y≦8, and 2≦Z≦5.) is.

[0045] Examples of alloys of the present invention include, for example, AlSiB2, AlSi6B2, AlSi5B2, AlSi6Ti7B3, AlSi6Ti4B2, AlSi7Ti8B4, and AlTi0.3.

[0046] Examples of preferred alloys of the present invention include, for example, AlSi6Ti7B3, AlSi6Ti4B2 and AlSi7Ti8B4.

[0047] In a second object of the present invention, a method for producing the alloy of the present invention is described.

[0048] In particular, the alloy can be obtained by direct casting of the constituent elements - aluminum, silicon, titanium and boron.

[0049] Alternatively, the alloy can be obtained by casting from a suitable binary aluminum alloy (the "parent" alloy), then adding the appropriate amount of the missing element and casting again.

[0050] For purposes of the present invention, binary aluminum alloys ("parent" alloys) can include, for example, aluminum-titanium alloys (e.g., AlTi10, AlTi15), or aluminum-boron alloys (e.g., AlB4, AlB6, AlB10).

[0051] In a preferred aspect of the present invention, the casting temperature exceeds 660°C, and in a more preferred aspect, it is 700 to 900°C.

[0052] Analysis of the alloys obtainable by the method of the present invention revealed that they contained Al (matrix), Si, Fe (trace amounts) and Ti (trace amounts), as well as AlTiSi, TiB2, AlB 12 The presence of metallic and intermetallic constituents represented as AlB2, AlSiFe (Fe is introduced as an impurity present in the parent alloy or in the molten metal preparation) was shown.

[0053] In the present invention, the order of elements reflects the concentration of the elements in the compound; for example, in the case of the intermetallic AlTiSi, the element concentrations are in the order [Al] > [Ti] > [Si]. Similarly, the intermetallic compound SiTiAl is mainly composed of silicon, followed by titanium and aluminum.

[0054] The intermetallic compound is represented, for example, by TiAl2.55Si0.45.

[0055] For trace amounts, the concentration of each element is less than 0.5% (w / w).

[0056] In a preferred aspect, the trace elements are present as oxides (e.g., MgO, Fe2O3).

[0057] In a preferred aspect of the invention, the alloy obtainable by the above method exhibits the presence of ceramic precipitates.

[0058] Such (“noble”) ceramic deposits are characterized by a higher corrosion potential than the matrix in which they are embedded, i.e., they are electrochemically more noble than aluminum.

[0059] In a particularly preferred aspect of the invention, the alloy obtainable by the above process exhibits the presence of non-stoichiometric aluminum and / or titanium borides.

[0060] In the present invention, the non-stoichiometric aluminum boride and / or titanium boride can be represented by Al1.67B22 and Ti0.93B2.

[0061] A combination of metallographic analysis and EDXS (Energy Dispersive X-ray Spectroscopy) measurements shows that the alloy thus obtained consists of an aluminum matrix in which metallic and intermetallic elements are dispersed (see Figure 3).

[0062] The following table shows examples of alloys obtained by casting the appropriate parent alloy and adding aluminum and / or silicon.

[0063] The casting temperature dictated the appropriate intermetallic constituents, the presence and composition of which was confirmed by EDXS and metallographic analysis.

[0064] [Table 1]

[0065] In a third object of the present invention, the alloy thus obtained can be used to manufacture an anode.

[0066] For this purpose, the alloy can be gravity cast using a suitable mold.

[0067] In another aspect of the invention, anodes made from the above metal alloys can be used in conjunction with cathodes to fabricate batteries.

[0068] The particular aluminum alloy produced in accordance with the present invention is characterized electrochemically and metallographically as follows:

[0069] a. Electrochemical characteristics The aluminum alloys produced according to the present invention were characterized by aluminum plating / stripping measurements in a suitable electrolyte.

[0070] The measurements reproduce the behavior of an aluminum battery anode half-cell and reveal the reversibility and efficiency of the oxidation / reduction reactions occurring at the battery anode.

[0071] For reference, the measurement results of a) a pure aluminum electrode; and b) an electrode made of EN-43200 (T6) alloy (10 wt%) AlSi10Mg(Cu) (UNI EN 1676), which contains silicon as the main alloying element, are also shown.

[0072] Specifically, measurements were performed using a three-electrode configuration as follows: 1) working electrode (WE): an alloy sample of the present invention with a known area; 2) counter electrode (CE): an aluminum foil (99.8%) with an area at least twice that of the WE; 3) reference electrode: an alloy sample of the present invention.

[0073] The electrolyte used was a solution of 1-ethyl-3-methylimidazolium chloride and AlCl3 in a molar ratio of 1:1.5 at 25°C, which is commonly used as an electrolyte for aluminum batteries.

[0074] The scan rate is 50 mV / s.

[0075] Aluminum plating / stripping measurements allow evaluation of the interfacial properties of the electrode in contact with the electrolyte.

[0076] In particular, a negative current induces a reduction reaction (Al) combined with Al plating from the electrolyte. 3+ + 3e - → Al 0 ), and the positive current is related to the oxidation reaction (Al 0 → Al 3+ + 3e - ) and is related to the injection of aluminum ions from the anode into the electrolyte.

[0077] The results are shown in the table below and in the graph in Figure 2.

[0078] [Table 2]

[0079] The results reveal a) a high current density, b) the presence of a well-defined peak (narrow and of medium height), and c) a reduction-oxidation potential close to 0 mV compared to Ref, which needs to be pursued and is associated with high reactivity, reversibility and efficiency of the investigated electrodes.

[0080] From the data it can be seen that all of the alloys of the present invention exhibit significantly higher redox current densities than aluminum alone.

[0081] In particular, the peak current (when oxidized) of the alloy of Example 6 is about 30 times that of aluminum.

[0082] Furthermore, the voltammetric profile of alloy Ref1 shows less pronounced peaks and negligible currents compared to the alloys of the invention and pure aluminum.

[0083] The EN-43200 alloy contains 9-11 wt% silicon, about 0.15 wt% titanium, and no boron.

[0084] This evidence supports the fact that the superior electrochemical performance of the alloys of the present invention is obtained through the synergistic effect of the presence of silicon, titanium and boron.

[0085] In particular, for the binary alloys (AlB2 and AlTi6), the anodic peak current is significantly higher than that of aluminum, but the peak potential is only slightly higher, which indicates that the reversibility of the oxidation reaction is low.

[0086] Considering the peak current and anodic peak potential as figures of merit, it can be seen that the ternary alloy (AlSi6B2) and quaternary alloys (AlSi6Ti7B3, AlSi6Ti4B2, AlSi7Ti8B4) show the best performance.

[0087] Therefore, the performance of these materials is related to the coexistence of boron and silicon, or silicon, boron and titanium in the aluminum matrix, which contributes to the formation and dispersion of appropriate phases and intermetallic compounds in the aluminum matrix and is particularly effective in adjusting the reversibility of the oxidation / reduction reaction of aluminum, resulting in increased reactivity and efficiency of the alloy.

[0088] b. Metallographic characteristics The image in Figure 3 shows the metallographic analysis of the AlSi7Ti8B4 alloy (Example 6).

[0089] This alloy was obtained by reaction (at 850°C) of two parent alloys AlTi15 and AlB10 with addition of silicon, with final element concentrations (in wt%) of Si: 7%, Ti: 8% and B: 4%.

[0090] By combining metallographic analysis and EDXS measurements, the alloys were identified as AlTiSi, SiTiAl, TiB2, and AlB 12 It was shown to consist of an aluminum matrix with dispersed AlB2, Ti, Fe, Si, and AlSiFe phases.

[0091] The formation of these phases, which are responsible for the electrochemical performance described in this patent application, can be optimized by selecting alloying elements based on the phase diagram and employing appropriate casting temperatures.

[0092] This manipulation results in a specific microstructure that allows for the advantageous electrochemical properties described.

[0093] c. Battery testing The performance of the AlSi6Ti8B4 alloy used as an anode was tested by galvanostatic cycling of a prototype CR2032 battery. The results in Figure 4 show the reversible behavior of the battery, with the specific capacity increasing from 13 mAh / g (after 1 cycle) to 34 mAh / g (after 100 cycles) and the discharge plateau near 600 mV. This trend indicates that promising cycling performance can be achieved by using the proposed quaternary AlSi6Ti8B4 alloy.

[0094] From these descriptions, the advantages offered by this patent application are immediately apparent.

[0095] The use of aluminum allows for the solution of a significant problem associated with the manufacture of lithium-ion batteries.

[0096] First, aluminum has four times the volumetric energy content, is harmless to humans, requires less energy to produce, and is abundant in the earth's crust, so requires less soil movement during mining.

[0097] The technology for producing, manufacturing, recycling and disposal of aluminum-based batteries is well advanced.

[0098] Furthermore, it is not flammable in air, ensuring high safety of the battery and the device containing it.

[0099] Therefore, the supply of aluminium has lower risks associated with its supply in geopolitical terms than lithium and other elements (e.g. nickel, cobalt) used in battery production.

[0100] The aluminum alloy developed in this invention for anode production can be used as an alternative to pure aluminum, preventing the formation of a passivating oxide layer on the electrode surface and reducing the Al 3+ It can form a high surface energy interface that promotes plating / stripping, improve the structural stability of the electrode by limiting the destruction process after cycling, limit dendritic growth, and generate a galvanic microcoupling phenomenon that can tune the reactivity of the electrode surface by limiting the passivation of the electrode surface and promoting ionic conduction at the interface with the electrolyte.

[0101] These performances of the proposed alloy clearly surpass the prior art in this field and demonstrate that it will enable the realization of energy densities previously unattainable in the aluminum battery industry.

Claims

1. General formula: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 0≦X≦10, 0≦Y≦10, and 2≦Z≦5.) A metal alloy represented by A metal alloy obtained by a process comprising the direct casting of the constituent elements or the casting of a binary aluminum alloy to which the missing element has been added, said casting being carried out at a temperature between 700 and 900°C.

2. General formula: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 5≦X≦10, 0≦Y≦10, and 2≦Z≦5.) 10. A metal alloy obtainable according to the preceding claims, having

3. General formula: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 5≦X≦10, 4≦Y≦8, and 2≦Z≦5.) 10. A metal alloy obtainable according to the preceding claims, having

4. 10. A metal alloy obtainable according to any one of the preceding claims, selected from the group comprising AlSi6B2, AlSi6Ti7B3, AlSi6Ti4B2 and AlSi7Ti8B4.

5. Si, AlTiSi, TiB ２ , AlB １２ , AlB ２ 10. A metal alloy obtainable according to any one of the preceding claims, further comprising metallic and intermetallic constituents represented by AlSiFe, Fe (trace amounts) and Ti (trace amounts).

6. 10. A metal alloy obtainable according to any one of the preceding claims, comprising non-stoichiometric aluminum boride and / or non-stoichiometric titanium boride.

7. General formula: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 0≦X≦10, 0≦Y≦10, and 2≦Z≦5.) A method for producing a metal alloy represented by the formula: The method includes direct casting of constituent elements or casting of a binary aluminum alloy with the missing element added, the casting being carried out at 700-900°C.

8. General formula: AlSiXTiYBZ (wherein X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, and 0≦X≦10, 0≦Y≦10, and 2≦Z≦5.) A metal alloy represented by Si, AlTiSi, TiB ２ , AlB １２ , AlB ２ , AlSiFe, Fe (trace amounts), and Ti (trace amounts).

9. X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, with 5≦X≦10, 0≦Y≦10, and 2≦Z≦5; Si, AlTiSi, TiB ２ , AlB １２ , AlB ２ 10. The metal alloy of claim 9, further comprising metallic and intermetallic constituents represented by AlSiFe, Fe (trace amounts) and Ti (trace amounts).

10. X, Y, and Z are the weight percent of silicon, titanium, and boron, respectively, with 5≦X≦10, 4≦Y≦8, and 2≦Z≦5; Si, AlTiSi, TiB ２ , AlB １２ , AlB ２ 10. The metal alloy of claim 8 or 9, further comprising metallic and intermetallic constituents represented by AlSiFe, Fe (trace amounts) and Ti (trace amounts).

11. A metal alloy according to any one of claims 8 to 10, comprising non-stoichiometric aluminium boride and / or non-stoichiometric titanium boride.

12. A battery anode made from the metal alloy of any one of claims 1, 6 or 8-10.

13. A battery comprising an anode and a cathode, said anode being an anode according to the preceding claims.

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