Anode for magnesium battery and method for producing the same

Abstract

The invention relates to an anode (1) for a magnesium battery (2), comprising a core element (3) made of a core material, wherein a magnesium coating (4) is arranged at least partially on the surface of the core element (3), a protective layer (5) arranged on the surface of the magnesium coating (4). The invention also relates to a method for producing such an anode (1) and to a magnesium battery (2) comprising at least one such anode (1).

Description

Technical Field

[0001] This invention relates to the anode of a magnesium battery and a method for manufacturing the anode of a magnesium battery. A magnesium battery is an electrochemical storage device, and its anode is essentially made of magnesium. Background Technology

[0002] US2020 / 0112028A1 discloses an anode for a magnesium battery. The anode is formed of magnesium foam and has a polymer layer covering the magnesium foam on all surfaces.

[0003] US2016 / 0254541A1 describes electrode active materials for magnesium batteries containing the λ-MnO2 phase.

[0004] US2018 / 0190981A1 discloses an apparatus having a first electrode made of metallic magnesium and a coating comprising a first polymer.

[0005] JP2014143191A describes a magnesium battery having a negative electrode made of magnesium, a positive electrode made of copper or a copper alloy, and an electrolyte composed of citric acid, sodium chloride, and water. The side of the negative electrode facing away from the positive electrode is coated with a tin-containing coating.

[0006] It is generally known that magnesium batteries typically comprise multiple battery cells, each having multiple anodes and cathodes arranged in an electrolyte. During operation, a boundary layer forms on the magnesium anode between the electrolyte and the magnesium anode, which reduces the battery's lifespan and performance, particularly impedance and cycle stability. This boundary layer can form once the magnesium anode is exposed to ambient air. Summary of the Invention

[0007] The object of this invention is to provide a long-life anode for magnesium batteries. Furthermore, the anode should have low production costs and improve the performance of the magnesium battery. This object is achieved by the following subject matter. Preferred embodiments can be found in the specification and drawings.

[0008] The anode of the magnesium battery according to the invention comprises a core element made of a core material, wherein a magnesium coating is at least partially disposed on the surface of the core element, wherein a protective layer is disposed on the surface of the magnesium coating, and wherein the protective layer is any of the following:

[0009] - Designed to be metallic and formed from one of the following elements: aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, or

[0010] An alloy consisting of at least two of the following elements:

[0011] Aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, or

[0012] - Designed to be ceramic and composed of elements from the group consisting of aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, carbon, nitrogen, and oxygen, or

[0013] - The protective layer consists of a metal sulfide, wherein the metal sulfide is formed from at least one of the following elements from the group consisting of: aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, or

[0014] - The protective layer is composed of carbon or carbon-doped carbon.

[0015] In other words, at least a portion or the entire surface of the core element is coated with a magnesium coating, wherein the magnesium in the magnesium coating preferably has a purity of at least 99.9%. The magnesium coating is the active material of the anode. The active material is intended to interact with the cathode. A protective layer is disposed entirely on the surface of the magnesium coating. In particular, the protective layer is formed on the surface of the magnesium coating in such a way that the electrolyte of the magnesium battery does not directly (i.e., in close) contact the magnesium coating of the anode, but only contacts the protective layer disposed on the surface of the magnesium coating, or has a positive influence on the anode behavior due to the interaction with the magnesium coating. This has the advantage that no spontaneous boundary layer with respect to the electrolyte is formed on the magnesium coating, which reduces the lifespan and performance of the magnesium battery, particularly impedance and cycle stability. In particular, the protective layer protects the magnesium coating from oxidation during production. Furthermore, the protective layer achieves a reduction in interfacial resistance and an improvement in the kinetics of the dissolution and deposition processes. In addition, the protective layer optimizes the cycle performance of the anode.

[0016] To achieve these benefits, the protective layer is designed to be metallic and preferably formed from one of the following elements: aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, and silver. Alternatively, the protective layer may be formed from an alloy of at least two of the following elements: aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, and silver.

[0017] For example, the protective layer is formed of aluminum or an aluminum alloy. For example, the protective layer is formed of copper or a copper alloy. For example, the protective layer is formed of a tin alloy. For example, the protective layer is formed of silicon or a silicon alloy. For example, the protective layer is formed of titanium or a titanium alloy. For example, the protective layer is formed of tantalum or a tantalum alloy. For example, the protective layer is formed of niobium or a niobium alloy. For example, the protective layer is formed of nickel or a nickel alloy. For example, the protective layer is formed of molybdenum or a molybdenum alloy. For example, the protective layer is formed of silver or a silver alloy.

[0018] In an alternative embodiment, the protective layer is designed to be ceramic and composed of elements from the group consisting of aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, carbon, nitrogen, and oxygen.

[0019] Specifically, the ceramic protective layer is a metal oxide layer. For example, the protective layer is at least partially or completely formed of aluminum oxide. For example, the protective layer is at least partially or completely formed of copper oxide. For example, the protective layer is at least partially or completely formed of tin oxide. For example, the protective layer is at least partially or completely formed of silicon oxide. For example, the protective layer is at least partially or completely formed of titanium oxide. For example, the protective layer is at least partially or completely formed of tantalum oxide. For example, the protective layer is at least partially or completely formed of niobium oxide. For example, the protective layer is at least partially or completely formed of nickel oxide. For example, the protective layer is at least partially or completely formed of molybdenum oxide. For example, the protective layer is at least partially or completely formed of silver oxide.

[0020] In another preferred embodiment, the ceramic protective layer is formed of carbide and / or nitride compounds. For example, the protective layer is at least partially or completely formed of silicon nitride. For example, the protective layer is at least partially or completely formed of titanium nitride. For example, the protective layer is at least partially or completely formed of niobium nitride. For example, the protective layer is at least partially or completely formed of tantalum nitride.

[0021] In another alternative embodiment, the protective layer comprises a metal sulfide, wherein at least one element selected from the group consisting of aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, and silver forms the metal sulfide. For example, the protective layer is at least partially or entirely formed of molybdenum sulfide.

[0022] According to another preferred embodiment, the protective layer may include sulfide and / or nitride compounds.

[0023] In an alternative embodiment, the protective layer consists of carbon or carbon-doped carbon. The maximum total amount of doping in the carbon-doped layer (i.e., the protective layer mainly composed of carbon) is 45 atomic percent. Preferably, one or more elements from the group consisting of aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, and hydrogen are used as doping elements.

[0024] According to a preferred embodiment of the invention, the protective layer has a thickness of at least 0.5 nm and at most 5 μm. In particular, it has been found that a protective layer thickness of at least 5 nm and at most 250 nm is particularly helpful in maintaining the energy density of the anode.

[0025] Preferably, the core element, also referred to as the conductor, is at least partially formed of aluminum, copper, steel, or a polymer material. For example, the core element is formed of aluminum or an aluminum alloy. For example, the core element is formed of copper or a copper alloy. For example, the core element is formed of steel or a steel alloy. In particular, the steel alloy is stainless steel (i.e., steel with a purity of at most 0.025 wt% sulfur and phosphorus content). In particular, the steel alloy is corrosion-resistant and contains at least chromium and / or nickel as alloying elements. For example, the alloy composition of the steel alloy can be determined by optical emission spectrometry (OES) or by X-ray fluorescence analysis (XRF). wt% is an abbreviation for weight percentage.

[0026] The following method steps are performed to produce the anode according to the invention: First, a core element is provided. The core element is preferably formed from a core material derived from aluminum, copper, steel, or a polymer material. Subsequently, a magnesium coating is applied to at least a portion of the surface of the core element. Then, a protective layer is applied to the surface of the magnesium coating.

[0027] According to a preferred embodiment of the present invention, a magnesium coating is applied to at least a portion or all of the surface of the core element by means of electroplating, lamination, PVD, CVD, ALD, plating, thermal spraying or melting processes.

[0028] The magnesium coating preferably has a layer thickness in the range of 50 nm to 200 μm (especially 1 μm to 50 μm).

[0029] For example, in an electroplating process, the electrochemical electrolysis of magnesium on the core element takes place in a deposition bath. In a lamination process, coating materials (e.g., a magnesium coating and a protective layer) are transferred or laminated onto the structured core element. In a plating process, a metal layer, also known as a cladding, is formed on the substrate or core element by pressure and temperature, and particularly also by subsequent heat treatment. In a thermal spraying process, liquefied magnesium is sprayed onto the substrate (i.e., the core element).

[0030] PVD is an abbreviation for "Physical Vapor Deposition." The PVD process is performed under vacuum and at temperatures ranging from 150°C to 500°C. A physical process is used to convert the starting material for the magnesium coating into a gaseous phase. The gaseous material is then directed to the surface of a core element, where it condenses and forms a magnesium coating. For example, in the PVD process, particles are extracted from a magnesium target by sputtering in a plasma and then transported to the surface of the core element. The PVD process can be used to produce particularly pure and homogeneous coatings.

[0031] CVD is an abbreviation for "Chemical Vapor Deposition". In the CVD process, a layer is deposited on the heated surface of a core element due to a chemical reaction originating from the gas phase. The CVD process is characterized by at least one reaction on the surface of the core element. This reaction involves at least one gaseous starting compound and at least two reaction products, at least one of which is in the solid phase. The CVD process can be used to produce particularly uniform coatings.

[0032] ALD is an abbreviation for "Atomic Layer Deposition." The ALD process is a highly modified CVD process with a self-confined surface reaction performed in at least two cycles. The material to be deposited is chemically combined with one or more carrier gases. These carrier gases are alternately fed into the reaction chamber, where they react with the surface of the core element, and then magnesium bound in the gas is deposited on the surface of the core element. The ALD process can be used to produce particularly thin coatings.

[0033] For example, in a melting process, magnesium is melted and applied to the core element by dipping or spraying. The melting process offers not only cost advantages but also the advantages of rapid formation and large-area coating.

[0034] According to a preferred embodiment of the present invention, a protective layer is applied to the entire surface of the magnesium coating by a PVD process, a CVD process, or an ALD process.

[0035] Alternatively, a protective layer can be coated onto magnesium foil, which is then applied to the core element. The magnesium foil is preferably produced using a rolling process.

[0036] According to a preferred embodiment of the invention, a protective layer is applied to the surface of the magnesium coating during anode operation. In other words, the battery cell is designed such that a protective layer is formed on the magnesium coating of the anode during magnesium battery operation, protecting the magnesium coating from oxidation, optimizing anode cycle performance, reducing interfacial resistance, and improving the kinetics of the dissolution and deposition processes. For example, the electrolyte is formed by depositing one of the following elements as a protective layer on the magnesium coating of the anode: aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, and silver. Alternatively, an alloy of at least two elements from the group consisting of aluminum, copper, tin, silicon, titanium, tantalum, niobium, nickel, molybdenum, and silver is deposited.

[0037] Furthermore, the present invention relates to a magnesium battery including an anode according to the invention. In particular, the magnesium battery has a plurality of battery cells, wherein each battery cell has a plurality of anodes and cathodes arranged in a liquid electrolyte or a solid electrolyte.

[0038] Cathodes made from cathode materials containing sulfur have proven suitable for use with anodes according to the invention. V₂O₅ or MgMn₂O₄ have proven particularly suitable as base materials for the intercalation reaction used to form the cathode. Sulfur-permeated carbon, sulfur-carbon compounds, or SPAN (sulfurized poly(acrylonitrile)) have proven particularly suitable as base materials for the conversion reaction used to form the cathode.

[0039] For the formation of electrolytes in magnesium batteries, electrolyte salts such as the following have proven to be suitable:

[0040] MgTFSI2 Bis(trifluoromethanesulfonylimide)magnesium

[0041] Mg(B(hfip)4)2 tetratetra(hexafluoroisopropoxy)magnesium borate

[0042] Mg(BH4)2 magnesium borohydride

[0043] In addition, mixtures of Mg(BH4)2 and Li(BH4) (=lithium borohydride) or Mg(B(hfip)4)2 and Li(B(hfip)4) (=lithium tetratetrafluoroisopropoxy)borate) have been shown to improve performance.

[0044] Furthermore, the use of electrolyte salts based on Mg(HMDS)2 (=bis(hexamethyldisil magnesium nitride)) has proven to be appropriate.

[0045] Polyvinyl ethers, especially TEG (tetraethylene glycol dimethyl ether, tetraethylene glycol), DEG (diethylene glycol dimethyl ether, diethylene glycol), DME (1,2-dimethoxyethane, ethylene glycol dimethyl ether, monoethylene glycol), or mixtures of TEG and DME, have proven to be suitable solvents for dissolving electrolyte salts.

[0046] Other proven solvents are THF (tetrahydrofuran) or ionic liquids (such as Pyr). 14 TFSI (=1-Butyl-1-methylpyrrolidone bis(trifluoromethanesulfonyl)imide) Attached Figure Description

[0047] The following description, in more detail, illustrates further measures to improve the invention and a preferred exemplary embodiment of the invention based on two figures, wherein the same elements are provided using the same reference numerals. In the figures:

[0048] Figure 1 A highly simplified schematic cross-sectional view of the magnesium battery according to the invention, shown only partially, is illustrated.

[0049] Figure 2 A highly simplified schematic cross-sectional view of the anode according to the invention, shown only partially, is presented. Detailed Implementation

[0050] Figure 1 A magnesium battery 2 according to the invention is shown in a highly simplified manner. The magnesium battery 2 has a plurality of battery cells 8, wherein, for simplicity, only a portion of a single battery cell 8 is shown herein. The battery cell 8 has a plurality of anodes 1 and cathodes 7 arranged in an electrolyte 6. The surface of the respective anode 1 is completely covered by a protective layer 5.

[0051] Figure 2 It shows according to Figure 1 The anode 1 has a cross-section. The anode 1 has a core element 3, which is formed of aluminum as the core material. A magnesium coating 4 is disposed on the surface of the core element 3 as the active material of the anode 1, wherein the magnesium coating 4 is formed, for example, by a melting process. A protective layer 5 is disposed on the surface of the magnesium coating 4. For example, the protective layer 5 is metallic and formed of aluminum, or ceramic and formed of copper oxide. In particular, a PVD process is suitable for forming the protective layer 5. The protective layer 5 preferably has a layer thickness of at least 0.5 nm and at most 5 μm. The electrolyte 6 is not adjacent to the magnesium coating 4, but only to the protective layer 5. This increases the lifespan of the anode 1 and improves the performance of the magnesium battery 2.

[0052] List of reference numerals

[0053] 1 Anode

[0054] 2 Magnesium batteries

[0055] 3-core components

[0056] 4 Magnesium coating

[0057] 5 protective layers

[0058] 6 Electrolytes

[0059] 7 Cathode

[0060] 8 battery cells

Claims

1. An anode (1) of a magnesium battery (2), comprising: A core element (3) made of a core material, wherein a magnesium coating (4) is arranged at least partially on a surface of the core element (3), wherein a protective layer (5) is arranged on a surface of the magnesium coating (4), characterized in that the protective layer (5) is one of the following cases: - is designed as a metal and consists of one of the following elements: aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, or an alloy of at least two of the following elements: aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, or - is designed as a ceramic and consists of an element from the group comprising aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, carbon, nitrogen, oxygen, or - the protective layer (5) consists of a metal sulfide, wherein the metal sulfide is formed by at least one of the following elements from the group comprising aluminum, copper, silicon, titanium, tantalum, niobium, nickel, molybdenum, silver, or - the protective layer (5) consists of carbon or doped carbon.

2. The anode (1) according to claim 1, characterized in that the ceramic protective layer (5) is a metal oxide layer.

3. The anode (1) according to claim 1, characterized in that the ceramic protective layer (5) is formed by a carbide and / or nitride compound.

4. The anode (1) according to any one of the preceding claims 1 to 3, characterized in that the protective layer (5) has a layer thickness of at least 0.5 nm and at most 5 pm.

5. The anode (1) according to any one of the preceding claims 1 to 3, characterized in that the magnesium coating (4) has a layer thickness in the range of 50 nm to 200 pm.

6. The anode (1) according to any one of the preceding claims 1 to 3, characterized in that the core material is formed by at least one material from the group comprising aluminum, copper, steel, and a polymeric material.

7. A method for producing the anode (1) according to any one of claims 1 to 6, comprising at least the following method steps: - providing the core element (3), - applying the magnesium coating (4) to at least a portion of a surface of the core element (3), and - applying the protective layer (5) to a surface of the magnesium coating (4).

8. The method according to claim 7, characterized in that the magnesium coating (4) is applied to at least a portion of a surface of the core element (3) by means of an electroplating process, a lamination process, a PVD process, a CVD process, an ALD process, a plating process, a thermal spraying process, or a melting process.

9. The method according to claim 7 or 8, characterized in that the protective layer (5) is applied to a surface of the magnesium coating (4) by means of an electroplating process, a PVD process, a CVD process, a plating process, or an ALD process.

10. A magnesium battery (2) comprising: at least one anode (1) according to any one of claims 1 to 6 and at least one cathode (7) made of a cathode material comprising a sulfur component.

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