Anodes comprising tin and aluminum

Abstract

The present invention relates to an electrochemical cell comprising: an anode comprising tin (Sn) and aluminum (Al); a cathode; and an electrolyte. The present invention also relates to a method of preparing an anode comprising tin and aluminum for an electrochemical cell.

Description

[0001] Anodes Comprising Tin and Aluminum

[0002] Technical Field

[0003] The present disclosure generally relates to anodes comprising tin and aluminum, and more particularly relates to electrochemical cells comprising such anodes. The present disclosure also relates to methods of producing such anodes.

[0004] Background

[0005] Lithium-ion batteries have been used widely in various applications due to their high energy density and cycling stability. However, the limited availability of lithium resources and safety concerns have prompted researchers to seek alternative energy storage devices. Among them, aqueous aluminum metal batteries (AAMBs) have garnered significant attention due to the favorable characteristics of aluminum (Al). Firstly, Al is the most abundant metal element in the Earth's crust, making it more sustainable than other metals. Secondly, Al exhibits reduced chemical reactivity compared to lithium or sodium, enhancing the safety profile of AAMBs, especially when employing aqueous electrolytes. Thirdly, AAMBs offer one of the highest theoretical energy densities owing to the ability of an Al ion to transfer three electrons during redox reactions. Moreover, Al benefits from a well-established manufacturing industry, enabling the potential for cost reduction, which is vital for practical applications.

[0006] However, AAMBs face challenges arising from the relatively negative reduction potential of Al (-1.66 V). This characteristic leads to the hydrogen evolution reaction (HER) on the batten 's anode side during the charging process, significantly impeding the reversibility of Al anodes. Additionally, the spontaneous formation of an oxidation / passivation layer on the Al surface hampers the charge transfer kinetics and increases the battery's internal resistance. Combined, these factors diminish the Coulombic efficiency and lifespan of AAMBs, thereby rendering their overall performance far from satisfactory.

[0007] Anode engineering is an effective strategy for enhancing AAMB performance. Several practices have been reported in this regard. One approach involves the application of an artificial solid electrolyte interphase (SEI) on the surface of the Al electrode. However, the SEI layer may dissolve during cycling, rendering it ineffective. Another technique is the combination of Al with other metals. Aluminum-zinc (Zn) alloy anodes can be prepared by depositing Al on Zn foil in Al(OTF)j electrolytes or by depositing Zn on Al foil in Al(OTF)3+HOTF+Zn(OTF)2 mixed electrolytes. However, it is essential to note that Zn2+is also a multivalent metal ion with energy storage activity, thus making this type of battery more accurately described as a hybrid battery. Copper (Cu) and cerium (Ce) have also been selected to prepare Al-Cu and Al-Cc cutcctic alloys, consisting of alternating a-Al and intermetallic lamcllas. These lamcllas can serve as electron transfer pathways and provide guidance for Al deposition. The use of such eutectic alloys can enhance the reversibility of Al deposition. However, the preparation process involves energy-intensive arc melting. Another approach comprises using anodes comprising amorphous Al. Amorphous Al exhibits a lower nucleation energy barrier for Al deposition and enables fast interfacial ion transfer kinetics, thereby suppressing HER and promoting Al deposition. Nevertheless, the preparation process of this approach involves alloying and dealloying with lithium, which compromises the concept of "beyond lithium" batteries. Furthermore, the preparation process is relatively complex and time-consuming, hindering practical application scalability.

[0008] Thus, there is a need to provide an electrochemical cell that overcomes, or at least ameliorates one or more of the disadvantages described above. Summary

[0009] In an aspect of the present disclosure, there is provided an electrochemical cell comprising: an anode comprising tin (Sn) and aluminum (Al); a cathode; and an electrolyte.

[0010] In another aspect of the present disclosure, there is provided a method of preparing an anode comprising tin and aluminum for an electrochemical cell, the method comprising:

[0011] (a) layering Sn foil and Al foil;

[0012] (b) folding the layered foils; and

[0013] (c) applying pressure to compress the folded layered foils, wherein the thickness of the compressed folded layered foils of step (c) is thinner than the thickness of the folded layered foils of step (b).

[0014] Advantageously, the electrochemical cell disclosed herein may demonstrate high voltage plateaus, Couloumbic efficiencies and capacity, while maintaining a high capacity retention and stable cycling.

[0015] Further advantageously, the anode comprising Sn and Al exhibits good Al stripping and plating ability. The inventors have surprisingly found that the Al matrix may act as a rich source of Al ions during the stripping process, while the Sn skeleton may offer an abundance of active sites for Al underpotential deposition (UPD) during plating.

[0016] In an embodiment, the anode comprises a Sn-Al composite which is a laminated metal composite. Advantageously, the space and gaps between layers of the laminated metal composite can increase the electrode's specific surface area and enhance ion transport.

[0017] In another embodiment, the anode comprises a polymer disposed on at least a portion of the surface of the anode. Advantageously, the polymer may enhance the corrosion resistance of the anode. The inventors have also surprisingly found that disposing a polymer on the anode may suppress Al passivation while still promoting stripping and plating of Al.

[0018] Further advantageously, the disclosed method provides a low-cost and easy way of producing such anodes, while at the same time producing anodes capable of high capacity and stability.

[0019] Definitions

[0020] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry described herein, arc those well- known and commonly used in the art.

[0021] Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements. As used herein, the term “composite” refers to a material made from two or more constituent components with different physical or chemical properties that, when combined, produce a material having characteristics which are different from the characteristics of the individual components. The individual components remain separate and distinct within a finished structure of the composite at the macro- or micro-scale levels.

[0022] As used herein, the term “laminated metal composite” refers to a material composed of layers of metal or metal alloys. The laminated metal composite may be obtained by bonding multiple layers of different metals or metal alloys together. The layers may be bonded together by rolling, pressing, or adhesive bonding.

[0023] The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.

[0024] As used herein in the specification and in the claims, the phrase "at least," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a nonlimiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and / or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0025] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

[0026] As used herein, the term "about", in the context of concentrations of components of the formulations, typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically, + / - 2% of the stated value, even more typically + / - 1 % of the stated value, and even more typically + / - 0.5% of the stated value.

[0027] Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub -ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0028] Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments witii a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0029] Brief Description of Drawings

[0030] The accompanying drawings illustrate disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0031] Fig. 1

[0032] Fig. 1 is a series of diagrams, with (a) showing an illustration of ineffective Al deposition onto a bulk Al surface in an aqueous solution, (b) showing a depiction of the underpotential deposition (UPD) of Al on Sn / Cu. (c) and (d) showing energy dispersive X-ray spectroscopy (EDS) mappings of an Sn foil and a Cu foil respectively after cyclic voltammetry (CV) testing in a three-electrode system, and (e) showing the cycling performance of a comparative embodiment (Sn|0.5 M AhCSChhlALMnCh full cell).

[0033] Fig. 2

[0034] Fig. 2 is a spectrogram showing the EDS analysis of carbon paper after CV testing in a three -electrode system.

[0035] Fig. 3

[0036] Fig. 3 is a series of diagrams showing the preparation and characterization of an embodiment of the present invention (Sn@Al foil), with (a) illustrating the process of preparing said embodiment, (b) showing the X- ray diffraction (XRD) patterns of said embodiment and its precursors (Sn and Al foils), (c) showing the X- ray photoelectron spectroscopy (XPS) Al 2p spectra of said embodiment, (d) showing the XPS Sn 3ds / 2 spectra of said embodiment, (e) showing the top-view scanning electron microscopy (SEM) secondary electron images and EDS mappings of said embodiment, and (f) showing the cross-sectional SEM backscattered electron images of the localized structure of said embodiment.

[0037] Fig. 4

[0038] Fig. 4 is a series of diagrams, with (a) being photographs showing an embodiment of the present invention (Sn@ Al foil), and its precursors (Sn and Al foils), and (b) showing the typical voltage profiles of full cells using Sn@Al anodes, prepared with different folding / rolling times, and AI MnCF cathodes at a specific current of 100 mA g

[0039] Fig. 5

[0040] Fig. 5 is a spectrogram showing the XPS survey spectrum of an embodiment of the present invention (Sn@Al foil).

[0041] Fig. 6

[0042] Fig. 6 is a series of spectra, with (a) showing the XPS Al 2p spectra of Al foil, and (b) showing the XPS Sn 3ds / 2 spectra of Sn foil.

[0043] Fig. 7

[0044] Fig. 7 is a series of diagrams showing the electrochemical performance of an embodiment of the present invention (Sn@Al foil) and a comparative embodiment (bare Al), with (a) showing the CV curves of symmetric cells utilizing the respective anodes at a scan rate of 10 mV s'1, (b) showing the slab models used for theoretical calculations and corresponding adsorption energy of Al atoms on Al and Sn substrates, (c) showing the Nyquist plots of symmetric cells with the respective anodes, (d) showing the voltage profiles of the symmetric cells with the respective anodes in 0.5 M AbCSChh electrolyte, cycled at a current density of 0.05 mA cm2and an areal capacity of 0.1 mAh cm2.

[0045] Fig. 8

[0046] Fig. 8 is a series of graphs showing the Nyquist plots and equivalent circuit fitting of (a) an embodiment of the present invention (Sn@ Al), (b) a comparative embodiment (bare Al), and a second embodiment of the present invention (p-Sn@Al) symmetric cells.

[0047] Fig. 9

[0048] Fig. 9 is a graph showing the voltage profiles of symmetric cells with an embodiment of the present invention (Sn@Al electrode) and a comparative embodiment (bare Al electrode) in a 0.5 M Ah(SO4)3 electrolyte, cycled at current densities of 0.05, 0.1 , and 0.2 mA cm2while maintaining an areal capacity of 0.1 mAh cm2.

[0049] Fig. 10

[0050] Fig. 10 is a series of diagrams, with (a) showing a schematic of the stripping / plating process of an embodiment of the present invention (Sn@Al electrode) and a comparative embodiment (Al electrode), (b) showing a cross-sectional SEM image and EDS mappings of said embodiment of the present invention after 500 stripping / plating cycles, (c) showing the top-view SEM image of said comparative embodiment after 300 stripping / plating cycles, and (d) showing the XPS Al 2p spectra of said embodiments after the stripping / plating cycle.

[0051] Fig. 11

[0052] Fig. 11 is a series of spectra, with (a) showing the XPS survey and (b) showing the Sn 3ds / 2 spectra of an embodiment of the present invention (Sn@ Al electrode) after stripping / plating cycling.

[0053] Fig. 12

[0054] Fig. 12 is a series of diagrams, with (a) showing the XRD pattern and (b) showing the SEM image of MnO powder.

[0055] Fig. 13

[0056] Fig. 13 is a series of graphs, with (a) showing the CV curves of an embodiment of the present invention (Sn@Al||AliMnO2 cell) and a comparative embodiment (Al||AlxMnC>2), (b) showing the Nyquist plots of said embodiments, (c) showing typical voltage profiles of said embodiments at a specific current of 100 mA g1, (d) showing the cycling performance of said embodiments at a specific current of 100 mA g '. (c) showing rate performance of said embodiments, (f) showing the typical voltage profiles of a second embodiment of the present invention (Sn@Al||KNHCF cell) and a second comparative embodiment (A1||KNHCF cell) at a specific current of 100 mA g-1, (g) showing the cycling performance of said second embodiments at 100 mA g ’, and (h) showing the OCV comparison of full cells with a third embodiment of the present invention (Sn@Al anode), and third and fourth comparative embodiments (Sn and Al anodes) paired with MnO and KNHCF cathodes.

[0057] Fig. 14

[0058] Fig. 14 is a series of graphs showing the Nyquist plots and equivalent circuit fitting of (a) an embodiment of the present invention (Sn@Al||Al,MnO2 cell), and (b) a comparative embodiment (Al||ALMnO2 cell).

[0059] Fig. 15

[0060] Fig. 15 is a series of diagrams, with (a) showing the XRD pattern and (b) showing the SEM image of KNHCF powder. Fig. 16

[0061] Fig. 16 is a graph showing the rate performance of an embodiment of the present invention (Sn@ A1||KNHCF cell) and a comparative embodiment (A1||KNHCF cell).

[0062] Fig. 17

[0063] Fig. 17 is a series of diagrams showing the characterization and electrochemical performance of an embodiment of the present invention (p-Sn@Al electrode), with (a) showing the cross-sectional SEM image of said embodiment, (b) showing the Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FT1R) of said embodiment and a second embodiment of the present invention (Sn@ Al electrode), (c) showing contact angle measurements of said embodiments with 0.5 M AlzCSO^s aqueous solution, (d) showing the linear polarization curves of said embodiments in symmetric cells using a 0.5 M AhlSOpi electrolyte, and (e) showing the cycling performance of a third embodiment of the present invention (p-Sn@Al||KNHCF cell) at a specific current of 100 mA g

[0064] Fig. 18

[0065] Fig. 18 is a series of graphs showing the Nyquist plots and equivalent circuit fitting of (a) a comparative embodiment (A1||KNHCF cell), (b) an embodiment of the present invention (Sn@ A1||KNHCF cell) and (c) a second embodiment of the present invention (p-Sn@Al||KNHCF cell).

[0066] Fig. 19

[0067] Fig. 19 is a schematic showing the function of a hydrophobic polymer coating in an embodiment of the present invention (p-Sn@Al anode).

[0068] Fig. 20

[0069] Fig. 20 is a series of images showing the top-view SEM images of embodiments of the present invention after cycling, with (a) showing a p-Sn@Al anode, and (b) showing a Sn@Al anode.

[0070] Fig. 21

[0071] Fig. 21 is a series of spectrograms showing the EDS analyses of (a) Sn foil after CV testing in a three- clcctrodc system, (b) Sn foil after immersion in the electrolyte, (c) Cu foil after CV testing in a three - electrode system, (d) Cu foil after immersion in the electrolyte, (e) Ni foil after CV testing in a three - electrode system, and (f) Ni foil after immersion in the electrolyte.

[0072] Fig. 22

[0073] Fig. 22 is a photograph showing the incompatibility of Cu and Al foils during a rolling process.

[0074] Detailed Disclosure of Embodiments

[0075] Aqueous aluminum metal batteries (AAMBs) typically face problems relating to the promotion of the hydrogen evolution reaction (HER) during the charging process due to the large negative reduction potential of Al. Additionally, the use of aqueous electrolytes may cause spontaneous formation of an oxidation / passivation layer on the Al surface, which hampers the charge transfer kinetics and increases the battery's internal resistance. The Coulombic efficiency and lifespan of AAMBs are hence negatively affected by these factors.

[0076] Additionally, the challenge of achieving sufficient Al deposition in aqueous solutions presents a significant hurdle for aqueous Al batteries, as shown in Fig. la which depicts ineffective Al deposition onto a bulk Al surface in an aqueous solution. In an initial investigation, Al deposition onto carbon paper was assessed using cyclic voltammetry (CV) testing within a three-electrode system. As illustrated in Fig. 2, energy dispersive X-ray spectroscopy (EDS) analysis yielded no detectable Al signal, emphasizing the challenge of Al deposition in aqueous solution. To overcome this, a promising approach is incorporating foreign metals to achieve the UPD of Al.

[0077] However, it was found that the planar substrate of metal foils gives low capacity. For example, Sn foils were employed as the current collector in the anode side for assembling coin cells, and the electrochemical performance was evaluated. As illustrated in Fig. le, the full cell displayed a limited specific capacity of <42 mAh g '. This is because foil has a restricted surface area. Once Al covers the surface, the UPD effect is gone, as illustrated in Fig. lb. Given the limitations of planar foils in providing surface area and capacity, the inventors have surprisingly found that combining Sn with Al foils in a hierarchical structure increases the interface between Sn and Al.

[0078] Herein, the present invention provides an electrochemical cell comprising an anode comprising Sn-Al as a solution for overcoming the hydrogen evolution reaction (HER) at the anode when charging the electrochemical cell, as well as the spontaneous formation of an oxidation / passivation layer on the surface of an Al anode. The inventors have surprisingly found that the electrochemical cell disclosed herein demonstrates high voltage plateaus, Coulombic efficiencies and capacity, while maintaining a high capacity retention and stable cycling.

[0079] The present invention provides an electrochemical cell comprising: an anode comprising tin (Sn) and aluminum (Al); a cathode; and an electrolyte.

[0080] In some embodiments, the anode may comprise a Sn-Al composite. In some embodiments, the anode may consist essentially of a Sn-Al composite. In some embodiments, the anode may consist of a Sn-Al composite.

[0081] The inventors have surprisingly found that the selection of Sn may provide tire composite with properties suited for use as an anode. For example, Sn may exhibit good interfacial adhesion with Al, which may advantageously allow them to tightly bond under pressure with the same elongation. Sn may also have a higher work function than Al, which may allow underpotential deposition (UPD) of Al to take place on a Sn surface. The UPD of Al ions on the Sn surface may allow improved Al stripping. Additionally, Sn may form a localized galvanic couple with Al, which may promote Al stripping, reduced internal resistance, and improved charge transfer kinetics. Sn may also have a higher overpotential required for hydrogen evolution, which may suppress the hydrogen evolution reaction (HER) at the anode. Sn may possess good ductility, which may allow it to avoid breaking during preparation. Further, Sn may be stable in mild acidic electrolytes, which may allow it to be used in the electrochemical cell without being replaced for a large number of cycles. The cost of Sn is low, which may allow the electrochemical cell to be produced at a lower cost.

[0082] Planar foils were found to provide limited surface area and capacity for the UPD of Al ions for Sn. It was found that when the Al was fully deposited over the Sn foil, it results in the loss of the UPD effect. The inventors have surprisingly found that when the metals (for example, Sn and Al) are in a multilayered structure, such as a laminated metal composite, it may advantageously activate the Al.

[0083] In some embodiments, the composite may be a laminated metal composite. The laminated metal composite may comprise multiple layers of different metals or metal alloys. The layers may be arranged in an alternating manner. In some embodiments, the metals may comprise Sn and Al. In some embodiments, the laminated metal composite may comprise at least 3 to 8193 layers, for example, about 3 layers to about 8193 layers, from about 3 layers to about 8000 layers, from about 3 layers to about 7500 layers, from about 3 layers to about 7000 layers, from about 3 layers to about 6500 layers, from about 3 layers to about 6000 layers, from about 3 layers to about 5500 layers, from about 3 layers to about 5000 layers, from about 3 layers to about 4500 layers, from about 3 layers to about 4097 layers, from about 3 layers to about 4000 layers, from about 3 layers to about 3500 layers, from about 3 layers to about 3000 layers, from about 3 layers to about 2500 layers, from about 3 layers to about 2049 layers, from about 3 layers to about 2000 layers, from about 3 layers to about 1500 layers, from about 3 layers to about 1025 layers, from about 3 layers to about 1000 layers, from about 3 layers to about 900 layers, from about 3 layers to about 800 layers, from about 3 layers to about 700 layers, from about 3 layers to about 600 layers, from about 3 layers to about 513 layers, from about 3 layers to about 500 layers, from about 3 layers to about 400 layers, from about 3 layers to about 300 layers, from about 3 layers to about 257 layers, from about 3 layers to about 200 layers, from about 3 layers to about 129 layers, from about 3 layers to about 100 layers, from about 3 layers to about 65 layers, from about 3 layers to about 33 layers, from about 3 layers to about 17 layers, from about 3 layers to about 9 layers, from about 3 layers to about 5 layers, or from about 5 layers to about 8193 layers, from about 9 layers to about 8193 layers, from about 17 layers to about 8193 layers, from about 33 layers to about 8193 layers, from about 65 layers to about 8193 layers, from about 100 layers to about 8193 layers, from about 129 layers to about 8193 layers, from about 200 layers to about 8193 layers, from about 257 layers to about 8193 layers, from about 300 layers to about 8193 layers, from about 400 layers to about 8193 layers, from about 500 layers to about 8193 layers, from about 513 layers to about 8193 layers, from about 600 layers to about 8193 layers, from about 700 layers to about 8193 layers, from about 800 layers to about 8193 layers, from about 900 layers to about 8193 layers, from about 1000 layers to about 8193 layers, from about 1025 layers to about 8193 layers, from about 1500 layers to about 8193 layers, from about 2000 layers to about 8193 layers, from about 2049 layers to about 8193 layers, from about 2500 layers to about 8193 layers, from about 3000 layers to about 8193 layers, from about 3500 layers to about 8193 layers, from about 4000 layers to about 8193 layers, from about 4097 layers to about 8193 layers, from about 4500 layers to about 8193 layers, from about 5000 layers to about 8193 layers, from about 5500 layers to about 8193 layers, from about 6000 layers to about 8193 layers, from about 6500 layers to about 8193 layers, from about 7000 layers to about 8193 layers, from about 7500 layers to about 8193 layers, from about 8000 layers to about 8193 layers, or at least about 3 layers, at least about 5 layers, at least about 9 layers, at least about 17 layers, at least about 33 layers, at least about 65 layers, at least about 100 layers, at least about 129 layers, at least about 200 layers, at least about 257 layers, at least about 300 layers, at least about 400 layers, at least about 500 layers, at least about 513 layers, at least about 600 layers, at least about 700 layers, at least about 800 layers, at least about 900 layers, at least about 1000 layers, at least about 1025 layers, at least about 1500 layers, at least about 2000 layers, at least about 2049 layers, at least about 2500 layers, at least about 3000 layers, at least about 3500 layers, at least about 4000 layers, at least about 4097 layers, at least about 4500 layers, at least about 5000 layers, at least about 5500 layers, at least about 6000 layers, at least about 6500 layers, at least about 7000 layers, at least about 7500 layers, at least about 8000 layers, at least about 8193 layers, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0084] Advantageously, the laminated metal composite may comprise a structure that allows the anode to exhibit good Al stripping and plating ability. The inventors have surprisingly found that the Al matrix may act as a rich source of Al ions during the stripping process, while the Sn skeleton may offer an abundance of active sites for Al UPD during plating. The inventors have also surprisingly found that the space and gaps between layers can increase the electrode’s specific surface area and enhance ion transport.

[0085] In some embodiments, the composite may be of Formula (I): SnyAlz— Formula (I)

[0086] In some embodiments, the ratio of y : z in Formula (I) may be in a range of about 0.10 : 1 to about 0.80 : 1 , from about 0.10 : I to about 0.75 : I , from about 0.10 : 1 to about 0.70 : 1 , from about 0.10 : 1 to about 0.65 : 1 , from about 0.10 : 1 to about 0.60 : 1 , from about 0.10 : 1 to about 0.55 : 1 , from about 0.10 : 1 to about 0.50 : 1 , from about 0.10 : 1 to about 0.45 : 1 , from about 0.10 : 1 to about 0.40 : 1 , from about 0.10 : 1 to about 0.35 : 1 , from about 0.10 : 1 to about 0.30 : 1 , from about 0.10 : 1 to about 0.25 : 1 , from about 0.10 : 1 to about 0.20 : 1 , from about 0.10 : 1 to about 0.15 : 1 , or from about 0.15 : 1 to about 0.80 : 1 , from about 0.20 : 1 to about 0.80 : 1 , from about 0.25 : 1 to about 0.80 : 1 , from about 0.30 : 1 to about 0.80 : 1 , from about 0.35 : 1 to about 0.80 : 1 , from about 0.40 : 1 to about 0.80 : 1 , from about 0.45 : 1 to about 0.80 : 1 , from about 0.50 : 1 to about 0.80 : 1 , from about 0.55 : 1 to about 0.80 : 1 , from about 0.60 : 1 to about 0.80 : 1 , from about 0.65 : 1 to about 0.80 : 1 , from about 0.70 : 1 to about 0.80 : 1 , from about 0.75 : 1 to about 0.80 : 1 , or about 0.10 : 1 , about 0.15 : 1 , about 0.20 : 1 , about 0.25 : 1 , about 0.30 : 1 , about 0.35 : 1 , about 0.40 : 1 , about 0.45 : 1 , about 0.50 : 1 , about 0.55 : 1 , about 0.60 : 1 , about 0.65 : 1 , about 0.70 : 1 , about 0.75 : 1 , about 0.80 : 1, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub -ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). The inventors have surprisingly found when the ratio of y:z falls within the above values, the HER may be substantially suppressed during charging of the electrochemical cell.

[0087] In some embodiments, the electrochemical cell may be an aluminum ion battery. In some embodiments, the electrochemical cell may be an aqueous aluminum ion battery.

[0088] In some embodiments, the anode or composite may have a thickness in a range of about 20 pm to about 200 pm, from about 20 pm to about 190 pm, from about 20 pm to about 180 pm, from about 20 pm to about 170 pm, from about 20 pm to about 160 pm, from about 20 pm to about 150 pm, from about 20 pm to about 140 pm, from about 20 pm to about 130 pm, from about 20 pm to about 120 pm, from about 20 pm to about 110 pm, from about 20 pm to about 100 pm, from about 20 pm to about 90 pm, from about 20 pm to about 80 pm, from about 20 pm to about 70 pm, from about 20 pm to about 60 pm, from about 20 pm to about 50 pm, from about 20 pm to about 40 pm, from about 20 pm to about 30 pm, or from about 30 pm to about 200 pm, from about 40 pm to about 200 pm, from about 50 pm to about 200 pm, from about 60 pm to about 200 pm, from about 70 pm to about 200 pm, from about 80 pm to about 200 pm, from about 90 pm to about 200 pm, from about 100 pm to about 200 pm, from about 110 pm to about 200 pm, from about 120 pm to about 200 pm, from about 130 pm to about 200 pm, from about 140 pm to about 200 pm, from about 150 pm to about 200 pm, from about 160 pm to about 200 pm, from about 170 pm to about 200 pm, from about 180 pm to about 200 pm, from about 190 pm to about 200 pm, or about 20 pm, about 30 pm, about 40 pm, about 50 pm, about 60 pm, about 70 pm, about 80 pm, about 90 pm, about 100 pm, about 110 pm, about 120 pm, about 130 pm, about 140 pm, about 150 pm, about 160 pm, about 170 pm, about 180 pm, about 190 pm, about 200 pm, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub -ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0089] In some embodiments, the cathode may be selected from the group consisting of AlxMnO2, KNHCF, V2O5, and sulfur. The cathode may comprise AlxMnO2, KNHCF, V2Os, and sulfur. In some embodiments, the electrolyte may be an aqueous aluminum salt. In some embodiments, the electrolyte may be selected from the group consisting of AhCSO^s, and Al(OTf)3. In some embodiments, the electrolyte may be non-corrosive. A non-corrosive electrolyte may advantageously lead to less anodic dissolution of the Al in the laminated metal composite.

[0090] The inventors have also surprisingly found that disposing a polymer on the anode may suppress Al passivation while still promoting stripping and plating of Al.

[0091] In some embodiments, a polymer may be disposed on at least a portion of the surface of the anode.

[0092] Tn some embodiments, the polymer may be selected from the group consisting of PVDF, sulfonated tetrafluoroethylene based fluoropolymer-copolymer, and polyethylene glycol.

[0093] Advantageously, a polymer disposed on the anode may enhance the corrosion resistance of the anode. Electrochemical cells containing such anodes may exhibit a high capacity retention of about 80% even after a large number of cycles.

[0094] In some embodiments, the electrochemical cell may comprise: an anode comprising AliSnoe; a cathode comprising AhMnOz or KNHCF; and an electrolyte comprising A^SCUE.

[0095] The present invention provides a method of preparing an anode comprising tin and aluminum for an electrochemical cell, the method comprising:

[0096] (a) layering Sn foil and Al foil;

[0097] (b) folding the layered foils; and

[0098] (c) applying pressure to compress the folded layered foils, wherein the thickness of the compressed folded layered foils of step (c) is thinner than the thickness of the folded layered foils of step (b).

[0099] Advantageously, the disclosed method provides a low-cost and easy way of producing such anodes, while at the same time producing anodes capable of high capacity and stability.

[0100] Tn some embodiments, steps (b) and (c) may be repeated at least once. Tn some embodiments, steps (b) and (c) may be repeated in a range of about 1 time to about 12 times, from about 1 time to about 11 times, from about 1 time to about 10 times, from about 1 time to about 9 times, from about 1 time to about 8 times, from about 1 time to about 7 times, from about 1 time to about 6 times, from about 1 time to about 5 times, from about 1 time to about 4 times, from about 1 time to about 3 times, from about 1 time to about 2 times, or from about 2 times to about 12 times, from about 3 times to about 12 times, from about 4 times to about 12 times, from about 5 times to about 12 times, from about 6 times to about 12 times, from about 7 times to about 12 times, from about 8 times to about 12 times, from about 9 times to about 12 times, from about 10 times to about 12 times, from about 11 times to about 12 times, or about 1 time, about 2 times, about 3 times, about 4 times, about 5 times, about 6 times, about 7 times, about 8 times, about 9 times, about 10 times, about 11 times, about 12 times, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). Advantageously, when subjected to the number of folding / rolling cycles disclosed herein, the anode may be activated resulting in a high battery capacity, while remaining stable towards corrosion and exhibiting a low failure rate during the initial discharge.

[0101] In some embodiments, the method may further comprise:

[0102] (d) applying a polymer solution onto the compressed folded layered foils of step (c).

[0103] In some embodiments, the method may further comprise:

[0104] (e) applying an additional polymer solution onto the product of step (d).

[0105] In some embodiments, the polymer in the polymer solution may be selected from the group consisting of poly vinylidene fluoride (PVDF), and sulfonated tetrafluoroethylene -based fluoropol ymer-copol ymer.

[0106] Examples

[0107] Non-limiting examples of the invention and comparative examples will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

[0108] Materials and Methods

[0109] General characterization procedures

[0110] Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed using a field-emission SEM (JEOL JSM-7600F). X-ray diffraction (XRD) patterns were acquired using an X-ray diffractometer (Bruker D8 Advance) equipped with a Cu Ka radiation source (Z=l .5406 A). X-ray photoelectron spectroscopy (XPS) spectra were collected using an XPS spectrometer (Kratos Axis Supra) equipped with an Al Ka X-ray source. The contact angle was measured using the DataPhysics OCA 15Pro instrument. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was performed on a PcrkinElmcr Frontier FT1R spectrometer with ATR attachment.

[0111] General procedure for electrochemical measurements

[0112] 2032-type coin cells were assembled using Whatman GF / A glass microfiber filters as separators. Before use, the bare Al electrode was polished. The galvanostatic chargc / dischargc (GCD) measurements were performed using a Neware BTS4000 battery testing system. Cyclic voltammetry (CV) testing was conducted on an Autolab PGSTAT204 electrochemical workstation. In three-electrode system testing, graphite rod was used as the counter electrode, Ag / AgCl as the reference electrode, and 0.5 M AECSChja aqueous solution as the electrolyte. Electrochemical impedance spectroscopy (EIS) measurements were carried out over a frequency range of 100,000 Hz to 0.01 Hz with an amplitude of 10 mV. Equivalent circuit fitting for Nyquist plots was performed on NOVA software. All electrochemical testing was conducted at room temperature (25°C).

[0113] Adsorption Energy Calculations

[0114] The adsorption energy calculations were performed using density functional theory (DFT) with the Vienna Ab initio Simulation Package. The generalized gradient approximation by Perdew-Burke-Ernzerhof was utilized for the exchange-correlation potential. The plane wave cut-off energy was set to 520 eV, while the energy criterion for the iterative solution of the Kohn-Sham equation was established at 10 ’ eV. The atomic structures were relaxed until the residual forces on the atoms decreased below 0.01 eV / A. A slab model was employed to simulate the surfaces of Al or Sn metal, ensuring a vacuum thickness exceeding 25 A to prevent any interactions between the layers. The slab thickness was set to be greater than 15 A to minimize surface energy. DFT calculations were employed to investigate the adsorption energy of the Al atom on the (111) plane of Al metal and (001) plane of Sn metal.

[0115] Example 1 : Preparation and characterization of Sn@Al electrode

[0116] A Sn-Al composite (Sn@Al) was prepared using a repeated folding and rolling method, as illustrated in Fig. 3a. In general, Sn foil is layered on an Al foil and the foils are folded roughly in half. The foils are then compressed with a roller to reduce the thickness of the foils. This process is repeated to form a multilayered, laminated Sn-Al composite.

[0117] More specifically, a rectangular aluminum foil and a tin foil of the same size and with a thickness of 100 pm were cleaned with ethanol and stacked together. They were then folded in half along their length, with the tin layer on the outside. Subsequently, a roll squeezer was employed to roll the foils until the thickness of the Sn-Al foil was reduced to 100 pm. This folding and rolling process was repeated nine times, resulting in the Sn@ Al with a final thickness of 100 pm. This iterative process gradually increased the number of metal layers while their thickness decreased (Table 1). The Sn© Al foil was finally cut into squares of the corresponding size for electrochemical measurements.

[0118] The Sn and Al foils undergo crushing and reformation during the rolling process, forming an interlaced laminate structure. Due to Sn's excellent ductility and affinity to Al, the resulting Sn@ Al is a compact and integral piece, as shown in Fig. 4, which shows the Sn and Al bonded together, allowing direct interaction between the Sn and Al frameworks.

[0119] Table 1. Theoretical thickness calculation of layers, assuming equal thickness reduction ratio for Al and Sn.

[0120] Folding Layer Actual Thickness of each Thickness of top and times count layer count internal layer [pm] bottom Sn layers [pm]

[0121] 1 4 3 50 25

[0122] 2 8 5 25 12.5

[0123] 3 16 9 12.5 6.25

[0124] 4 32 17 6.25 3.12

[0125] 5 64 33 3.12 1.56

[0126] 6 128 65 1.56 0.781

[0127] 7 256 129 0.781 0.390

[0128] 8 512 257 0.390 0.195

[0129] 9 1024 513 0.195 0.098 n2n+12n+ 1 100 50

[0130] X-ray diffraction (XRD) patterns confirm that Sn@Al is a mixture of Sn and Al without the appearance of any new peaks (Fig.3b). X-ray photoclcctron spectroscopy (XPS) was conducted on Sn© Al, Al, and Sn foils to capture surface information. XPS survey spectrum show the presence of Al, Sn, and O elements in the as-prepared Sn@Al (Fig. 5). Analysis of the Al 2p spectra of Sn© Al (Fig. 3c) reveals the presence of peaks corresponding to metallic Al° and oxidized Ali+. Based on peak area fitting, the ratio of the oxidation state is considerably lower than that of the original Al foil (Fig. 6a). In the Sn 3ds / 2 spectra of Sn@Al (Fig. 3d), peaks corresponding to metallic Sn° and oxidized Sn are observed. Similarly, the oxidized Sn ratio is lower than the original Sn foil (Fig. 6b). These observations suggest that the surface oxide layer of Sn@Al is reduced compared to the original Al and Sn foils. This can be explained by the fact that during the rolling process, metals undergo plastic deformation and extension, while the brittle oxide layer can only respond to stress by fracturing. Commercial Al foil and Sn foil have an oxide film on the surface. After repeated rolling, the oxide layer is shattered and evenly distributed within the overall structure, resulting in a reduction of the surface oxide layer. Scanning electron microscope (SEM) image and energy-dispersive X-ray spectroscopy (EDS) mappings of the top view of Sn@Al indicate the coexistence of Sn and Al on the surface and their patterned distribution (Fig. 3e). The SEM cross-sectional image reveals a uniform and intact Sn@Al with a thickness of 100 pm (Fig. 3f). In the backscattered electron imaging mode, localized regions exhibit a layered structure of Sn and Al intermixture (Fig. 3g).

[0131] Example 2: Electrochemical performance of Sn@Al electrodes in symmetric cells

[0132] CV tests were conducted on Sn@Al and Al symmetric cells to compare the behaviors of Sn@Al and Al electrodes. Fig. 7a shows that the Al electrode exhibited an asymmetric curve, with a typical HER- shaped peak on the plating side (negative voltage), indicative of incapable Al plating and severe HER. On the stripping side (positive voltage), suppressed current density was observed, possibly due to the surface passivation layer. In contrast, the Sn@Al electrode displayed a more symmetric curve and enhanced current density, which can be attributed to improved Al stripping / plating. The enhanced Al plating can be explained by the UPD of Al ions on the Sn surface. At the same time, HER was suppressed due to a higher overpotential required for hydrogen evolution on Sn. The augmented Al stripping can be elucidated by the galvanic couple concept. This concept posits that when two metals with distinct electrode potentials come into contact in an electrolyte, the more reactive metal accelerates dissolution / stripping. The more -noble Sn and less-noble Al with different electrode potentials will form localized Al / Sn galvanic couples, effectively promoting Al stripping.

[0133] To investigate the feasibility of easier Al deposition onto Sn@Al electrode compared to bare Al electrode, density functional theory (DFT) is employed to calculate the adsorption energy of Al atoms on both Sn and Al substrates. The adsorption energy of a single Al atom on Al (111) and Sn (001) surfaces were compared as illustrated in Fig. 7b. The calculated adsorption energy for Al on Sn surface is -5.02 eV, which is significantly more negative than Al atom on Al surface (-2.28 eV). This result indicates that Al deposition is more favorable on Sn. This confirms that the nucleation barrier could be reduced for Al deposition on Sn surface.

[0134] Electrochemical impedance spectroscopy (EIS) measurements were performed on symmetric cells, namely Sn@Al||Sn@Al and A1||A1. The Nyquist plots obtained from these measurements exhibit a significant contrast, as shown in Fig. 7c, where the Al electrodes showed a substantially higher internal resistance as compared to Sn@Al electrodes. The charge transfer resistance (Rct) was determined by equivalent circuit fitting as 6.28 kfl for Al| | Al and 187 fl for Sn@Al||Sn@Al cells as shown and calculated in Figs. 8a and 8b. The difference can be attributed to the disparity in passivation layer coverage between the two electrodes. When the insulating passivation layer covers the Al electrode's surface, a significant energy barrier impedes the ingress of Al ions from beneath the passivation layer into the electrolyte. Consequently, the transfer kinetics of Al ions is greatly hampered. On the contrary, in the case of the Sn@Al electrode, the passivation layer is cither thinner or discontinuously distributed, resulting in a smaller energy barrier that needs to be overcome.

[0135] The long-term Al stripping / plating of Sn@ Al and bare Al electrodes was investigated in symmetric cells. When cycled at a current density of 0.05 mA cm2and an areal capacity of 0.1 mAh cir.2, the A1||A1 cell exhibited fluctuating overpotential around 0.6 V and eventually failed after 320 h (Fig. 7d). This large overpotential can be attributed to the accumulation of a passivation layer. Despite pre-polishing the bare Al foil, the formation of Al oxide cannot be prevented in an aqueous electrolyte environment. The failure after 320 h can be attributed to irreversible Al consumption. Since the amount of Al plating is smaller than Al stripping in each cycle due to the dominant HER, the Al electrode gradually becomes thinner until it loses sufficient contact with the coin cell case. Consequently, the internal resistance significantly increases or even leads to an open circuit. In contrast, the Sn@Al||Sn@Al cell can cycle for over 900 hours with a consistently smooth overpotential below 0.5 V (Fig. 7d). At higher current densities of 0.1 and 0.2 mA cm2, the overpotential of Sn@ Al||Sn@ Al cell remains lower than that of Al|| Al cell (Fig. 9). These results indicate that the Sn@Al electrode exhibits good Al stripping / plating ability within a certain current density range.

[0136] The superior performance of Sn@Al electrodes can be demonstrated through the schematic provided in Fig. 10a. The Sn@ Al structure is specifically designed to optimize the battery's performance. In this design, the Al matrix acts as a rich source of Al ions during the stripping process, while the Sn skeleton offers an abundance of active sites for Al underpotential deposition during plating. Space and gaps between layers can increase the electrode's specific surface area and enhance ion transport. The interconnected Sn framework within the electrode helps maintain structural stability. Additionally, more- noble Sn and less-noble Al with different electrode potentials form localized Al / Sn galvanic couples, effectively promoting Al stripping. Sn's high HER overpotential is crucial in minimizing hydrogen generation. Conversely, the bare Al electrode faces a significant energy barrier to traverse the passivation layer during stripping. During the plating process, the highly negative reduction potential of Al makes it difficult for Al to deposit. Consequently, HER is severe, significantly impairing the reversibility of the battery.

[0137] Postmortem SEM images of the Sn@ Al electrode reveal no significant changes in the layered Sn and Al distribution (Fig. 10b). However, numerous pits are observed on the Al electrode after cycling, which can be attributed to corrosion and irreversible Al consumption (Fig. 10c). After cycling, the XPS survey spectrum of the Sn@Al electrode exhibits an emerging S 2p peak originating from the AN SO ip electrolyte (Fig. Ila). The Sn 3d,, 2 spectrum shows a higher proportion of oxidation states than that observed after preparation, indicating increased Sn oxide on the surface during cycling (Fig. lib). Given that S11O2 is considered a semiconductor, the additional surface oxide layer formed during the Al stripping / plating process could introduce higher overpotentials in electronic conduction and ion diffusion, as reflected by the increased overpotential during the initial 300 h in Fig. 7d. The Al 2p spectra of Sn@Al and bare Al electrodes after cycling further reveal differences (Fig. lOd). In the case of the bare Al electrode, a symmetric peak is observed at 74.8 eV, corresponding to the Al 2p peak for A12O3 / A1(OH)3 / A1O(OH). This suggests the presence of a passivation layer, indicating either inefficient Al deposition or severe side reactions. Sn@Al electrode exhibits an asymmetric peak with lower binding energy, which can be deconvoluted to metallic Al° and oxidized Al3+. The significant presence of the Alupeak indicates efficient Al deposition on the Sn@ Al electrode.

[0138] Example 3: Electrochemical properties of Sn@Al electrodes in full cells

[0139] Example 3a: Preparation ofMnO cathode

[0140] 4 g of potassium permanganate was dissolved in a 2.5 M sulfuric acid solution (200 mL) and stirred for 2 h at 75 °C. The resulting precipitate was collected through centrifugation, thoroughly washed with deionized water and ethanol, and dried overnight in a vacuum oven at 60 °C. The precursor was reduced in a tube furnace under a hydrogen atmosphere at 400 °C for 10 hours, yielding brown MnO powder. To prepare a manganese oxide cathode slurry, MnO powder, carbon black(Super-P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 6:2:2. N-methyl-2-pyrrolidone (NMP) was added appropriately, and the mixture was stirred overnight. The resulting slurry was coated onto hydrophobic carbon fiber paper and dried in a vacuum oven at 80°C for 12 hours. The loading mass of the active material was maintained at ~1 mg cm:.

[0141] Example 3b: Preparation of KNHCF cathode

[0142] 0.3 g of polyvinylpyrrolidone was introduced into 10 mL of a 0.07 M nickel(II) acetate tetrahydrate aqueous solution and stirred. Subsequently, 10 mL of 0.05 M potassium hexacyanoferrate(lll) aqueous solution was added dropwise into the mixed solution with continuous stirring for 2 hours. The precipitate was then collected by centrifugation, washed with deionized water, and dried at 60°C for 12 hours, yielding KNHCF powder.

[0143] To prepare a KNHCF cathode, KNHCF powder, Super-P. and carboxymethylcellulose (CMC) were blended in a weight ratio of 6:2:2 using deionized water. The mixture was then coated onto hydrophilic carbon fiber paper. The loading mass of the active material was ~1 mg cm2.

[0144] To prepare a 0.5 M electrolyte, 0.05 moles of aluminum sulfate octadccahydratc were dissolved in 100 mL of deionized water. For galvanostatic charge-discharge stability testing, an additive of 0.15 M manganese(H) sulfate was included to suppress the dissolution of manganese.

[0145] Example 3d: Electrochemical testing ofSn@Al electrodes in full cells

[0146] After confirming the superior performance of Sn@Al electrodes in symmetric cells, further tests of Sn@ Al anodes were conducted in full cells. A low-cost and fluorine-free aqueous ALGSCDs electrolyte was utilized. Manganese oxide (ALM11O2) was initially chosen as the cathode material due to its high capacity and redox potential. The MnO powder was prepared using the procedure described in our previous report. The XRD pattern and SEM image validate its phase and identify it as cubic with dimensions of 100 nm (Fig. 12). CV measurements were performed to evaluate the redox activity of Al||AlxMnO2 and Sn@Al||Al.YMnO2 cells at a scan rate of 0.1 mV s (Fig. 13a). Both bare Al and Sn@ Al cells exhibit a pair of redox peaks. However, notable differences were found in the peak positions. The reduction peak for Al||AlvMnO2cell appeared at 0.99 V. In contrast, for Sn@Al||ALMnO2cell. it was observed at 1.40 V. This increase of 0.41 V can be attributed to improved charge transfer kinetics and reduced internal resistance on the anode side during the discharging process. Moreover, the oxidation peak of the Sn@Al||AlrMnO2 cell is observed at 1.71 V, which is higher than the 1 .58 V of the Al||A1xMnO2 cell.

[0147] EIS testing was conducted to investigate the resistance of full cells. Fig. 13b illustrates a clear distinction in the Nyquist plots. Through equivalent circuit fitting (Fig. 14), the Rclof Sn@Al||ALMnO2 cell was determined to be 684 Q, significantly smaller than the value of 2.19 kf 2 for Al| | ALMnCL cell. This result indicates improved charge transfer kinetics at the electrode-electrolyte interface. Considering the cathodes remain the same, this improvement can be credited to enhanced interfacial transfer kinetics of the Sn@Al anode. Additionally, the solution resistance (Rs) and Warburg resistance (Zw) values are comparable between the two cells, owing to the use of the same electrolyte.

[0148] Subsequently, galvanostatic charge-discharge (GCD) testing was performed on Al||AlAMnO2 and Sn@Al||AlvMnO2 cells with the addition of 0.15 M MnSCL as an additive to inhibit the dissolution of manganese oxide cathode. Fig. 13c displays the typical voltage profiles at a specific current of 100 mA g Sn@Al||ALMnO2 cell demonstrates elevated charge and discharge voltage plateaus compared to AlHAlrMnCh cell, consistent with the trends observed in CV curves (Fig. 13a). Furthermore, the cycling performance of Sn@ Al||AlxMnO2 cell significantly surpasses that of Al||AlxMnO2 cell regarding capacity retention and Coulombic efficiency, as depicted in Fig. 13d. After 75 cycles, Sn@Al||AlxMnC>2 cell maintains a specific capacity of 177 mAh g1with a Coulombic efficiency of -95%. In contrast, Al||AlvMn02cell only offers a specific capacity of 46 mAh g1after 60 cycles with a Coulombic efficiency lower than 55%. The rapid capacity decay and subpar Coulombic efficiency of Al||AlxMnO2 cell can be attributed to the accumulation of a passivation layer and severe side reactions, primarily HER. Furthermore, we investigated the cycling performance of the Sn||AI .MnO: cell. However, Sn||AltMnO2 cell demonstrated limited electrochemical activity, as shown in Fig. le. This observation highlights Sris restricted energy storage capability in this system when utilizing a mildly acidic aluminum sulfate electrolyte. Therefore, in the case of cells with Sn@Al anodes, the capacity contribution from the Sn component can be disregarded. The capacity attenuation of Sn@ Al||A1xMnC>2 cell may be caused by the structural collapse of the cathode due to the strong electrostatic interaction of Al ions. The rate capability was assessed by cycling the cells at various specific currents, as shown in Fig. 13e. Sn@Al||AlvMnO2cell exhibits a specific capacity of -50 mAh g at 0.5 A g '. and when the current is reduced to 0.1 A g '. it recovers a capacity of -170 mAh g In contrast, Al||Al>MnO2 cell struggles to deliver capacity at 0.2 A g which can be attributed to the sluggish kinetics of the Al ions.

[0149] To assess the compatibility of the Sn@Al anode with different types of cathodes, its performance was evaluated when paired with a potassium nickel hcxacyanofcrratc (KNHCF) cathode The XRD pattern and the SEM image of the KNHCF powder is shown in Fig. 15. The KNHCF cathode, a Prussian blue analog (PBA), is characterized by limited capacity but enhanced stability. This unique characteristic complements the properties of manganese oxides. During discharging and charging at a specific current of 100 mA g1within a voltage range of 0.5-1.6 V, the voltage profiles of Sn@ A1||KNHCF cell demonstrate higher voltage plateaus compared to A1||KNHCF cell (Fig. 13f). Furthermore, Sn@Al||KNHCF cell exhibits an initial specific capacity of 50 mAh g1with a capacity retention of 72% over 90 cycles (Fig. 13g). Moreover, it demonstrates a high Coulombic efficiency of -95%, outperforming the performance of the A1||KNHCF cell. When the specific current is increased to 1 A g Sn@Al||KNHCF cell maintains capacity retention of -50%, while A1||KNHCF cell struggles to deliver capacity even at 0.5 A g1(Fig. 16). These results indicate that the Sn@Al anode has the potential to be compatible with PBA cathodes, thus expanding its applications as an anode for AAMBs.

[0150] The open-circuit voltage (OCV) for six full cells was then compared, as presented in Fig. 13h. Full cells with Sn anodes consistently exhibit the lowest OCV when paired with MnO or KNHCF cathodes. This observation can be easily understood, as the OCV is related to the electrochemical potential difference between the cathode and anode, and Sn possesses a relatively positive potential. On the other hand, cells with Al anodes theoretically should have a high OCV due to the negative potential of Al metal. However, in practice, they only offer OCV values slightly higher than those with Sn anodes, primarily due to the presence of a surface passivation layer. In contrast, cells employing Sn@Al anodes display an OCV approximately 0.3 V higher than their Al-anodc counterparts. This improvement is attributed to the activation of the Al metal in Sn@ Al anodes.

[0151] Example 4: Polymer Coated Electrode

[0152] Example 4a: Preparation of polymer coated Sn@Al (p-Sn@Al)

[0153] A 5 wt% solution of poly vinylidene fluoride (PVDF) was prepared by thoroughly stirring a certain amount of PVDF powder in V-methyl-2-pyrrolidone (NMP). Simultaneously, a Nafion™ 117 solution was added to dimethylformamide (DMF) and thoroughly mixed. Subsequently, the PVDF solution was first coated onto Sn@Al, followed by the coating of the Nafion solution. The solvent was then slowly dried on a hot plate at 60 °C for 1 h.

[0154] Example 4b: Evaluation of p-Sn@Al

[0155] The activation of Al brings significant benefits to the electrochemical performance of Sn@Al electrodes. However, it also gives rise to a challenge in the form of increased chemical reactivity between Al and the mildly acidic electrolyte (pH 2.5 for 0.5 M AF(SO));). Therefore, the synergy of passivation and the activation of Al needs to be balanced. A mixed polymer film made of Nafion and polyvinylidene fluoride (PVDF) was drop cast onto Sn@Al. The resulting electrode was denoted as p-Sn@Al. Fig. 17a illustrates the uniformity of the coating layer with a thickness of ~45 pm. The EIS test (Fig. 8c) shows that the Rciof p-Sn@Al||p-Sn@Al cell is 279 Q. Although this value represents a 49% increase compared to Sn@Al||Sn@ Al cell, it remains considerably smaller than the Al|| Al cell. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy on the polymer film was performed (Fig. 17b). The analysis revealed characteristic bands associated with PVDF and Nafion. Notably, the CFz vibration at 1180 and 875 cm1and the C 11 j vibration at 1405 cm1of PVDF were prominently observed. Additionally, the band at 1055 cm1corresponded to the SO s stretching vibration, while the band at 1150 cm indicated the CF2 stretching vibration of Nafion. Contact angle (CA) measurements were conducted to assess the alteration in wettability between p-Sn@Al and Sn@Al. Remarkably, p-Sn@Al exhibited a significantly larger CA of 90.5° compared to Sn@ Al’s CA of 50.6° (Fig. 17c). This difference indicates the hydrophobic nature of the coating, which potentially restricts the interaction of water molecules and Sn@Al from corrosion. This observation is consistent with the reported PVDF coating in aqueous batteries. Furthermore, linear polarization curves (Fig. 17d) demonstrated that the corrosion current (ican) of p-Sn@Al electrodes was lower than that of Sn@ Al electrodes, confirming the enhanced corrosion resistance conferred by the coating. With the advantages of the coating, p-Sn@Al||KNHCF cell exhibited a steady chargc / dischargc process for over 700 cycles, with high Coulombic efficiencies of >97% (Fig. 17e). Taking the 10thcycle capacity after stabilization as a reference, p-Sn@ A1||KNHCF cell maintained 82% of the capacity after 700 cycles. EIS testing and equivalent circuit fitting reveal tire introduction of a parallel resistance of 269 fl in p-Sn@Al||KNHCF attributed to the coating layer (Fig. 18). However, the overall resistance remains considerably lower than that of A1||KNHCF. Although the polymer coating may increase resistance and affect kinetics performance, it can impede the transfer of protons, thereby protecting the surface from HER and corrosion, as illustrated in Fig 19. The surface of the p-Sn@ Al electrode is intact after cycling, without cracks and fragments observed in the Sn@Al electrode, as shown in the SEM images in Figure 20.

[0156] Comparative Examples

[0157] Comparative Example 1: Preparing Cu@Al

[0158] Experiments were conducted in a three -electrode system to test Al deposition onto other metals, such as Sn, Cu and Ni. CV testing was performed using metal foils (Sn, Cu, Ni) as the working electrode. As shown in Figs. 1c, Id, 21a, and 21c, EDS analysis revealed distinct Al signals on Sn and Cu substrates. In contrast, Sn and Cu foils exhibited no Al signals after immersion in the electrolyte (Figs. 21 b and 21 d), excluding the Al source from electrolyte adsorption. Regarding Ni, the Al signal is weaker than Sn and Cu (Figs. 21e and 2 If).

[0159] Therefore, a Cu foil was subjected to the same process of rolling and folding with an Al foil as mentioned in Example 1. Experimental results demonstrated that Cu was incompatible with Al during the rolling process (Fig. 22). Specifically, Fig. 22 shows that Cu and Al foils cannot adhere together under pressure, and due to different ductility, they cannot uniformly elongate and form a well-contacted interface. In contrast, Sn and Al exhibits good interfacial adhesion, allowing them to tightly bond under pressure with the same elongation. Therefore, they can undergo repeated rolling processes.

[0160] Comparative Example 2: Sn@Al and p-Sn@Al versus Zn-AI

[0161] A Zn-AI anode was synthesized via depositing Al3+onto a Zn foil substrate. An electrochemical cell comprising the Zn-AI anode, an AlxMnO2cathode and an Al(OTf)3 electrolyte was assembled and compared with an electrochemical cell of the present invention.

[0162] From the results shown above, when the accompanying metal is changed from Zn to Sn in the anode, the capacity and retention of the electrochemical cell is improved, while the discharge plateau remains roughly constant. This comes together with the use of a less concentrated, non-corrosive Ah(SO4)3 electrolyte instead of Al(OTf)3.

[0163] Additionally, when the polymer coating is added to the anode (p-Sn@ Al), it can be seen that the retention of the electrochemical cell increases greatly, as compared to the Zn-AI anode. The retention of the electrochemical cell of the present invention is maintained at 82%, over twice the retention of the cell with the Zn-AI anode, even at almost 10 times the number of cycles.

[0164] Comparative Example 3: Prussian blue analog-based aqueous aluminum ion batteries

[0165] The voltage plateau and capacity retention of a p-Sn@ A1||KNHCF cell was compared with other known PBA-based AAMBs in the art and the results are displayed in Table 4. In contrast to other known AAMBs, the p-Sn@Al||KNHCF cell exhibited a steady charge / discharge process for over 700 cycles, with high Coulombic efficiencies of >97% (Fig. I9e). Taking the 10thcycle capacity after stabilization as a reference, p-Sn@ A1||KNHCF cell maintained 82% of the capacity after 700 cycles. It can thus be seen that the electrochemical cell of the present invention has a high discharge plateau while still maintaining a high capacity retention.

[0166] Industrial Applicability The present invention relates to electrochemical cells, particularly aqueous aluminum batteries. The electrochemical cells of the present invention possess high charge capacity while remaining stable over a long period of cycling. The electrochemical cells also have low productions costs. Thus, this invention is capable of industrial applicability It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

CLAIMS1. An electrochemical cell comprising: an anode comprising tin (Sn) and aluminum (Al); a cathode; and an electrolyte.

2. The electrochemical cell of claim 1, wherein the anode comprises a Sn-Al composite.

3. The electrochemical cell of claim 1 or 2, wherein the anode consists or consists essentially of a Sn-Al composite.

4. The electrochemical cell of claim 2 or 3, wherein the composite is a laminated metal composite.

5. The electrochemical cell of any one of claims 2 to 4, wherein the composite is a laminated metal composite comprising at least 100 layers.

6. The electrochemical cell of any one of claims 2 to 5, wherein the composite is of Formula (I):SnyAL — Formula (1); wherein the ratio of y : z is about 0.1 : 1 to about 0.8 : 1.

7. The electrochemical cell of claim 6, wherein the ratio of y : z is 0.4 : 1 to 0.8 : 1.

8. The electrochemical cell of any one of claims 1 to 7, wherein the electrochemical cell is an aluminum ion battery.

9. The electrochemical cell of any one of claims 1 to 8, wherein the anode or composite has a thickness of about 20 pm to 200 pm.

10. The electrochemical cell of any one of claims 1 to 9, wherein the cathode is selected from the group consisting of ALMnCh, KNHCF, V2O5, iodine, and sulfur.

11. The electrochemical cell of any one of claims 1 to 10, wherein the electrolyte is an aqueous aluminum salt.

12. The electrochemical cell of any one of claims 1 to 1 1 , wherein the electrolyte is selected from the group consisting of AhCSO^s, and Al(OTf)3.

13. The electrochemical cell of any one of claims 1 to 12, wherein a polymer is disposed on at least a portion of the surface of the anode.

14. The electrochemical cell of claim 13, wherein the polymer is selected from the group consisting of PVDF, sulfonated tetrafluoroethylene based fluoropolymer-copolymer, and polyethylene glycol.

15. The electrochemical cell of any one of claims 1 to 14, comprising: an anode comprising Al iSno.e; a cathode comprising AI. M11O2 or KNHCF; andan electrolyte comprising AlzCSO^.

16. A method of preparing an anode comprising tin and aluminum for an electrochemical cell, the method comprising:(a) layering Sn foil and Al foil;(b) folding the layered foils; and(c) applying pressure to compress the folded layered foils, wherein the thickness of the compressed folded layered foils of step (c) is thinner than the thickness of the folded layered foils of step (b).

17. The method of claim 16, wherein steps (b) and (c) are repeated at least once.

18. The method of claim 16 or 17, wherein steps (b) and (c) are repeated about 5 to 12 times.

19. The method of any one of claims 16 to 18, wherein the method further comprises:(d) applying a polymer solution onto the compressed folded layered foils of step (c).

20. The method of claim 19, wherein the method further comprises:(c) applying an additional polymer solution onto the product of step (d).

21. The method of claim 19 or 20, wherein the polymer in the polymer solution is selected from the group consisting of polyvinylidene fluoride (PVDF), and sulfonated tetrafluoroethylene-based fluoropolymer-copolymer.

22. The method of any one of claims 16 to 21, wherein the anode comprises a composite of any one of claims 2 to 9.

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