Electrodes with tapered alloy layers, batteries and methods

Abstract

The present disclosure relates to an electrode (1) for a secondary lithium metal battery, comprising a current collector (2), a negative metal layer (3) comprising lithium, and at least one tapered metal alloy layer (4a, 4b) extending along one or more opposite faces of the negative metal layer. The graded metal alloy layer comprises a mixture of lithium and another metal component, wherein a concentration of lithium relative to the another metal component decreases outwardly from the negative electrode metal layer. The invention also relates to a battery comprising the electrode and a manufacturing method thereof.

Description

Technical Field

[0001] The present disclosure relates to an electrode for a secondary battery, particularly a secondary lithium metal battery, a manufacturing method, and a battery including the electrode. Background Art

[0002] Rechargeable lithium-ion batteries (LiBs) are the technology of choice for today’s electric vehicles and renewable energy storage grids. To increase energy density, next-generation battery technologies tend to turn to lithium metal anodes, which have a potential high specific capacity of 3860 mAh / g and a redox potential of -3.04 V. These anodes can be combined with cathodes of various chemical choices such as NMC (lithium nickel manganese cobalt oxide), LFP (lithium iron phosphate), LNMO (lithium nickel manganese oxide), sulfur or air.

[0003] During charging, Li ions travel from the positive electrode through the electrolyte to the negative electrode, while Li metal (Li 0 ) deposits. During discharge, they return to the positive electrode. However, during the plating / stripping cycles, the cell experiences lithium loss due to adverse reactions of lithium with the electrolyte and / or due to the creation of porous or dendritic lithium deposits, which further creates an increasing risk of short circuits, reducing the operable cell life and performance.

[0004] J. Lou, et al. (Nanomaterials 11, 300, 2021) described a LiSn alloy anode composition that inhibits lithium dendrite growth. However, the layer only includes a single monolithic composition consisting of a relatively large amount of non-or non-optimal lithium-conducting material, which can be regarded as a burden in terms of electrical efficiency and does not participate in the battery reaction. In addition, the chemical-mechanical stability leaves room for improvement in both the mechanical expansion coefficient and the interlayer electric field lines.

[0005] C. Zhong, et al. (Materials Today Energy 18, 100528, 2020) describe various multi-element Sn-Co-Sb alloy negative electrodes with different ratios of Sn:Co:Sb for holding Li. The alloy composition is made by tilting the substrate. Therefore, the alloy composition is not uniform in any horizontal sub-plane parallel to the substrate. Therefore, in the vertical direction, the composition of each local point is different and consists of a relatively large amount of non-or non-optimal lithium conductive material that does not participate in the battery reaction (which is a burden in terms of electrical efficiency). Summary of the invention

[0006] The present disclosure aims to obviate or at least mitigate one or more of the above disadvantages by providing electrodes, methods and batteries as disclosed herein.

[0007] The present invention is also intended to provide a battery with improved performance and / or life by mitigating one or more of the following: adverse reactions of the negative electrode metal during manufacturing and / or adverse volume and surface changes during repeated insertion and extraction of Li during battery cycling, especially initial charging cycles. As explained in more detail below, the electrodes disclosed herein can advantageously contribute to achieving one or more of the above-mentioned goals.

[0008] According to a first aspect, an electrode is provided, specifically an electrode for a secondary lithium metal battery. The electrode comprises at least a current collector and a negative electrode metal layer extending along one or more faces of the current collector. The negative electrode metal layer comprises at least a battery active metal component, usually at least or substantially lithium metal. Optionally, the active metal component may contain other battery active metals, such as alkaline (earth) metals such as K, Na and Ca. The negative electrode metal layer comprises at least one graded metal alloy layer. The graded metal alloy preferably extends substantially conformally along one or more relative faces of the negative electrode metal layer.

[0009] Depending on the location of the graded metal alloy layer, the layer may be understood as a covering layer provided along the face of the negative electrode metal layer opposite the current collector, or as an intermediate layer extending between the negative electrode metal layer and the current collector.

[0010] The graded metal alloy layer comprises a mixture of a battery active metal component (usually lithium metal) and another metal component other than the active metal component. The other metal component may comprise one or more other metals (usually metals other than lithium) alloyed with the battery active metal component. The metal is generally selected to have at least a lower redox potential than the battery active negative electrode active composition. The abundance (e.g., concentration in vol%) of lithium (battery active metal) relative to another metal component decreases in a direction away from the interface with the negative electrode metal layer. In the direction orthogonal thereto (along the interface with the negative electrode metal layer), the relative abundance of the metals in the mixture is preferably constant.

[0011] The concentration of lithium (negative active metal) relative to the other metal component gradually decreases from a maximum value (eg, 100%) at the interface with the negative electrode metal layer to a minimum value (eg, 0%) at the interface across the thickness of the graded metal alloy layer.

[0012] Alternatively, or in addition, the lithium concentration gradually decreases from the surface of the negative electrode layer. Therefore, in some preferred embodiments, the tapered metal alloy layer can be provided as a multilayer stack comprising a plurality of sublayers, whereby in subsequent sublayers of the stack, the concentration of lithium metal (negative electrode metal) relative to another metal component decreases in a direction away from the negative electrode metal layer. Therefore, the tapered metal alloy layer and / or the negative electrode metal layer can be understood to form a laminate, for example, a nanolaminate.

[0013] Without wishing to be bound by theory, the inventors have found that the advantage of providing a graded layer comprising a mixture of a battery active metal component (usually lithium) and another metal component in addition to the active metal component involves forming a layer with anisotropic volume expansion. It is believed that this will inhibit the volume and surface changes of the negative electrode metal (e.g., Li) during repeated insertion and extraction during battery cycling, especially in the first and / or first cycle, thereby preventing the gradual degradation of the metal negative electrode layer.

[0014] Depending on the location below and / or above the negative electrode metal layer, the graded metal alloy layer can provide the function of a passivation layer and / or a seed layer.

[0015] It has been found that providing a metal alloy layer having a graded composition throughout the thickness advantageously reduces the total amount of material (the other metal component) that does not participate in the cell reaction without affecting the beneficial properties described herein.

[0016] As will be described in more detail below, the graded metal alloy layer acts as a seed layer, which can advantageously mitigate uneven negative electrode metal plating (particularly during the initial charge cycle and / or during subsequent charging operations during battery operation). In addition, the seed layer can allow for uniform stripping of negative electrode metal during battery discharge operations. These effects can advantageously contribute to a combination of improved battery performance, durability, and / or safety by reducing the formation of isolated negative electrode metal domains (so-called mossy domain structures) and / or reducing the formation or propagation of so-called dendrites.

[0017] When provided as a passivation layer, the graded metal alloy layer can advantageously mitigate degradation of the negative electrode metal, such as adverse reactions due to exposure to the environment (O2, CO2 and / or N2), which can lead to loss of battery active materials, particularly during battery assembly and / or electrode storage.

[0018] Therefore, in some preferred embodiments, the graded metal alloy layer is disposed between the current collector and the negative electrode metal layer, that is, as an interface layer between the current collector and the positive electrode metal layer, whereby the relative concentration of lithium in the mixture increases in a direction away from the current collector, preferably increasing to 100% at the interface with the negative electrode metal layer.

[0019] Therefore, in some other or further preferred embodiments, the graded metal alloy layer is provided along the surface of the negative electrode metal layer relative to the current collector, that is, arranged along the outer surface of the electrode relative to the current collector to engage with the separator of the battery system, wherein the relative concentration of lithium in the mixture decreases in the direction away from the negative electrode metal layer, preferably to substantially 0 vol%. The higher the relative amount of another negative electrode metal toward the outer interface, the better the protection of the underlying negative electrode metal (such as Li) from adverse reactions with the environment.

[0020] In a further preferred embodiment, the electrode includes a graded metal alloy layer along both faces of the negative electrode metal layer, i.e., a graded metal alloy layer along the interface between the current collector and the negative electrode metal layer, and another graded metal alloy layer along the outer surface of the electrode opposite to the current collector. The composition of the other metal component in each of these graded layers can be the same, but does not need to be the same. For example, the other metal component contained in the bottom (seed) layer can be selected to optimize the electrical contact with the current collector and provide optimal wetting for the subsequent negative electrode metal layer, while the other metal component contained in the top (passivation) layer can be selected to minimize the reactivity to the environment while being transgressive to the negative electrode metal or negative electrode metal ions (e.g., Li metal / ions).

[0021] According to another or further aspect, a secondary battery is provided, comprising an electrode as disclosed herein. The battery further comprises a separator and a counter electrode. The separator typically comprises an electrolyte composition, for example, a solid, semi-solid or liquid electrolyte composition. The battery may also comprise one or more of a negative electrode liquid composition and / or a positive electrode liquid composition. The negative electrode metal layer included in the electrode is provided with at least one graded metal alloy layer (above, below or on both sides). Depending on the position, the graded metal alloy layer advantageously provides the battery with the benefits described in terms of passivation, seeding or passivation and seeding.

[0022] In some embodiments, the battery is configured as a secondary negative metal battery, typically a secondary lithium metal battery (LMB), wherein the counter electrode comprises a layer of a positive electrode composition loaded with negative metal cations (LMB is lithium ions). In a preferred embodiment, the negative electrode metal layer has a thickness in the range of < 20 μm before the initial charge cycle of the battery. It is found that the amount of negative electrode metal (LMB is lithium) provided thereby provides an overall active anode metal inventory that provides an effective buffer for the potential loss of the replacement positive electrode composition during progressive battery cycling.

[0023] In other embodiments, the total active negative electrode metal inventory can be determined by the initial amount of negative electrode metal contained in the negative electrode metal layer (i.e., before initial battery cycling). For example, in one embodiment, the battery is configured as a secondary lithium air battery. In another embodiment, the electrode is used to assemble a secondary lithium sulfur battery (Li-S).

[0024] In either case, the amount of negative electrode metal is preferably such that the area capacity (mAh / cm 2) ≥ 1, preferably ≥ 4. In terms of thickness, the negative electrode metal layer has a thickness of preferably ≥ 5 μm, more preferably ≥ 20 μm or more, for example, up to 50 μm or 100 μm. When the negative electrode metal layer (e.g., Li) is distributed in the 3D structured negative electrode, the thickness can be appropriately adjusted.

[0025] According to a further aspect, there is provided a method of making an electrode as described herein. The method comprises: providing a current collector; depositing a negative electrode metal component comprising lithium into a layer, and one or more steps of depositing a graded metal alloy layer comprising a mixture of lithium and another metal component, wherein the concentration of lithium relative to the other metal component decreases from the negative electrode metal layer outward. The deposition of the graded metal alloy layer typically comprises co-depositing lithium (or another negative electrode metal component) and the other metal component.

[0026] In a preferred embodiment, the co-deposition comprises one or more of vapor deposition and electrochemical deposition.

[0027] In another or further preferred embodiment, the method includes repeatedly depositing a graded metal alloy layer comprising a mixture of lithium and another metal component to form the graded metal alloy layer into a multilayer stack comprising a plurality of subsequently deposited sublayers, whereby the lithium concentration in subsequent sublayers of the stack decreases in the direction of the first sublayer at the negative electrode metal layer.

[0028] In other or further preferred embodiments, preferably wherein the current collector is a flexible elongated foil, such as a metal or metal-coated foil, the method can advantageously be configured as a roll-to-roll process comprising passing the current collector through respective spatially separated stations, such as stations under a sufficiently regulated inert atmosphere (e.g., with little to no humidity, oxygen, CO2 and / or N2), to carry out the steps of depositing the negative electrode metal component and depositing the graded metal alloy layer (including sublayers, if any). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other features, aspects, and advantages of the apparatus, systems, and methods of the present disclosure will become better understood from the following description, appended claims, and accompanying drawings, in which:

[0030] Figure 1A A cross-sectional side view of a cathode metal layer and a graded metal alloy layer is provided;

[0031] Figure 1B and 1C A cross-sectional side view of an embodiment of an electrode including a current collector, a negative metal layer, and a graded metal alloy layer is provided;

[0032] Figure 2Aproviding a cross-sectional side view of an electrode including a graded metal alloy layer negative electrode along opposing sides of a negative electrode metal layer; and

[0033] Figure 2B A cross-sectional side view of an electrode including graded metal alloy layers provided as a multilayer stack is provided;

[0034] Figure 2C Step-type (left) and gradient-type (right) Li metal concentration profiles are shown;

[0035] Figure 3A and 3B A cross-sectional side view of the electrode is provided;

[0036] Figure 3C An exploded cross-sectional side view of a secondary lithium metal battery is provided; and

[0037] Figures 4A-4D A schematic diagram of a method for making an electrode is provided. DETAILED DESCRIPTION

[0038] The terms used to describe specific embodiments are not intended to limit the present invention. Unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" used herein are also intended to include plural forms. The term "and / or" includes any and all combinations of one or more listed related items. It should be understood that the terms "include" and / or "comprise" specify the presence of features, but do not exclude the presence or addition of one or more other features. It should be further understood that when a specific step of a method is referred to as a subsequent step of another step, unless otherwise stated, it can directly follow another step, or one or more intermediate steps can be performed before performing the specific step. Similarly, it should be understood that when describing the connection between structures or components, unless otherwise stated, such connection can be constructed directly or through intermediate structures or components.

[0039] The present invention will be described more fully below with reference to the accompanying drawings, in which embodiments of the invention are shown. In the accompanying drawings, the absolute and relative sizes of systems, components, layers and regions may be exaggerated for clarity. The embodiments may be described with reference to schematic and / or cross-sectional diagrams of possible idealized embodiments and intermediate structures of the present invention. In the specification and drawings, the same numbers always refer to the same elements. Relative terms and their derivatives should be interpreted as referring to the orientation shown in the drawings described at the time or discussed. These relative terms are for ease of description, and unless otherwise stated, the system is not required to be constructed or operated in a specific direction.

[0040] The electrode 1 will now be explained in more detail with reference to Figures 1-3B. Figure 3CAs explained, the electrode is particularly beneficial in the assembly of secondary negative metal batteries.

[0041] Electrode 1, such as Figure 1B , 1C , 2A, 2B, 3A and 3B, comprising: a current collector 2; a negative electrode metal layer 3; and at least one graded metal alloy layer 4, 4a, 4b. The negative electrode metal layer 3 comprises or is substantially composed of one or more elements selected from Na, K, Mg and / or Ca, preferably Li. The graded metal alloy layer comprises a mixture of one or more elements (preferably lithium) contained in the negative electrode metal layer 3 and another metal component, the other metal component comprising one or more other elements alloyed with the negative electrode metal as described above.

[0042] like Figure 1A As shown, the graded metal alloy layer 4 extends as a conformal layer along one or more opposing faces 31 , 32 of the negative electrode metal layer 3 .

[0043] If you will refer to Figure 2C To elaborate further, the vol % concentration or relative abundance of the negative electrode active material (eg, Li) relative to another metal component decreases outward from the interface between the negative electrode metal layer 3 and the graded metal alloy layer 4 .

[0044] The thickness t3 of the negative metal layer and the thickness t4, t4a, t4b of the graded metal alloy layer, as well as the position of the negative metal layer 3 and the graded metal alloy layer 4 relative to the current collector 2 generally depend on the intended application of the electrode, such as the type of battery system in which the electrode is to be used.

[0045] In one embodiment, for example, Figure 1B As shown, the negative electrode metal layer 3 is arranged as an intermediate layer extending between the current collector 2 and the graded metal alloy layer 4a. Therefore, the graded metal alloy layer 4a can be understood as a covering layer formed to face the environment before being assembled into a battery. Therefore, the graded metal alloy layer 4a forms a protective layer, a passivation layer, to alleviate adverse reactions (deterioration) of the underlying negative electrode metal layer 3, such as exposure to the environment before and / or during assembly into a battery system.

[0046] In another or further embodiment, for example, Figure 1C As shown, the graded metal alloy layer 4b is provided as an intermediate layer between the current collector 2 and the negative electrode metal layer 3. Therefore, the graded metal alloy layer 4b can be understood as a seed layer (e.g., such as a negative electrode metal component layer) formed by, for example, deposition before assembly into a battery system and / or by plating or charging paths as a component of the assembled battery system. Figure 3C as shown).

[0047] In yet further embodiments, for example, Figure 2A ,3A As shown in Figure 3C, the electrode 1 includes a first and a second graded metal alloy layer 4a, 4b, one of which constitutes a seed layer 4b, which is provided as an intermediate layer between the current collector 2 and the negative metal layer 3, and the other layer constitutes a passivation layer, which is provided along the surface of the negative metal layer 3 relative to the seed layer.

[0048] The other metal component includes one or more elements selected from zinc, magnesium and / or metals or metalloids of Groups 13-15, preferably one or more of Zn, Mg, Al, Ga, In, Sn, C, Ge, Si and / or Bi. An important aspect of the effect of suppressing volume change (reducing gradual change during battery cycling) is that the volume expansion of the resulting alloy is relatively reduced, so lower volume expansion is increasingly preferred. Therefore, the other metal component preferably includes one or more of indium (In), zinc (Zn), magnesium (Mg), bismuth (Bi) and / or tin (Sn), most preferably tin.

[0049] Ternary alloys (e.g., Li-Cu-Sn), quaternary alloys (e.g., Li-Al-ON) or higher are all possible. In this regard, reference may be made to the compositions disclosed in the article by Y. Zhu et al. in Adv. Sci. 1600517 (2017), which is incorporated herein by reference.

[0050] Preferably, the current collector comprises or consists essentially of a metal foil or a metal-coated polymer foil, preferably comprising copper (Cu), nickel (Ni), or a composite material comprising one or more thereof.

[0051] In some embodiments, the current collector can be a so-called 3D current collector or a composite 3D current collector, which includes a plurality of high aspect ratio conductive support elements oriented away from the foil (e.g., approximately vertically). For example, the conductive support elements can include vertically aligned carbon nanotubes, for example, a column array grown from catalyst seeds on a Cu foil. Thus, in some embodiments, the electrode includes a structured current collector comprising a plurality of conductive protrusions extending from a substrate and covered by a negative electrode metal layer and a graded metal alloy layer.

[0052] In some embodiments, the graded metal alloy layer has a thickness t4, t4a, t4b in the range of 5-500 nm. For the seed layer, the thickness t4b is preferably in the range of 5-25 nm. It is found that the seed layer with a thickness in this range can effectively alleviate volume expansion and act as a seed while minimizing the content of inactive metal.

[0053] When a graded metal alloy layer is provided along the surface of the negative electrode metal layer to interface with the battery's separator (as a passivation or protective layer), it is found that a thickness t4a of about 50–100 nm can effectively mitigate volume expansion during cycling and shield the environment with minimal content of inactive metals.

[0054] The thickness of the negative electrode metal layer t3 also depends on the intended application. In principle, the thickness can range from infinitely thin to up to 20 μm or more. Note that in some embodiments, the negative electrode metal layer can be part of the graded metal alloy layer, such as the outermost sublayer, or partially overlap with it.

[0055] In other or further embodiments, the negative electrode metal layer can be determined as a layer having a thickness of typically ≤ 20 μm, based on a predetermined amount of negative electrode metal. The amount of negative electrode metal provided can be understood as a buffer amount that replaces the loss of negative electrode metal from the total negative electrode metal inventory (e.g., defined by the positive electrode composition) during battery operation. In yet another or further embodiment, such as in an electrode configured as an assembly in a negative electrode metal-air battery (e.g., Li-air battery) or a negative electrode metal-sulfur battery (e.g., Li-S), the negative electrode metal layer can be determined as a layer having a thickness of typically ≥ 5 μm, based on the total negative electrode metal (e.g., Li) inventory of the system.

[0056] In some embodiments, for example, Figure 2C As shown in (right), the concentration of lithium (the negative electrode active metal) relative to the other metal component gradually decreases from a maximum value (e.g., 100%) at the interface with the negative electrode metal layer to a minimum value (e.g., 0%) at the interface across the thickness of the graded metal alloy layer.

[0057] Of course, the concentration of the negative active metal relative to the other metal component does not necessarily need to span the range from about 100% at the negative metal layer 3 to about 0% across the opposite interface of the graded metal alloy layer 4. Other ranges are also contemplated, for example, a range with an upper limit of about 90%, 80% or 70%, and / or a range with a lower limit of about 10%, 20% or 30%, such as 100%-10%, 100%-20%, 100%-30%, 90%-0%, 90%-10%, 90%-20%, 90%-30%, 80%-0%, 80%-10%, 80%-20%, 80%-30%, 70%-0%, 70%-10%, 70%-20% or 70%-30%.

[0058] However, for the passivation layer, it is strongly preferred that the concentration of the negative electrode active metal (eg, Li) be reduced to about 0% to mitigate adverse reactions, such as adverse reactions of lithium with the environment.

[0059] In some preferred embodiments, for example, Figure 2B and 2C As shown in (left), the graded metal alloy layer 4 is provided as a multilayer stack 4s including a plurality of sublayers 4-1, 4-2, 4-3, 4-n, whereby the concentration of lithium relative to another metal component in subsequent sublayers 4-2, 4-3, 4-n of the stack decreases starting from the first sublayer 4-1 on the negative electrode metal layer 3.

[0060] It has been found that providing the graded metal alloy layer and / or the negative electrode metal layer as a laminate can provide advantages in terms of uniformity across a production batch and reduced production complexity. Figure 4D As explained in further detail, the (nano)laminate can be provided particularly efficiently by a continuous manufacturing method, for example a roll-to-roll (R2R) method, whereby subsequent sub-layers are provided at spatially separated and preferably air-excluded processing units (for example, an R2R production line comprises a plurality of deposition units, which can each be configured to deposit a specific mixture of a given sub-layer).

[0061] Alternatively or additionally, a continuous or at least semi-continuous gradient, e.g. Figure 2C (left) can be provided by one or more processing units (e.g., deposition stations) configured to time-regulate deposition parameters.

[0062] Advantageously, the electrode can be implemented as a double-sided electrode. For example, by providing a negative electrode metal layer as disclosed herein and at least one graded metal alloy layer along two opposite sides (front and back) of a common current collector. Alternatively, a double-sided electrode can be provided by back-to-back positioning of two single-sided electrodes. The double-sided electrode can be advantageously used in the manufacture and assembly of batteries that increase energy density by providing an integrated electrode stack.

[0063] Figure 3A An embodiment of a double-sided electrode 1 is shown, which includes a first negative electrode metal layer as disclosed herein and at least one graded metal alloy layer along a first side 21 of a single electrode foil 2, and a second negative electrode metal layer as disclosed herein and at least one graded metal alloy layer along a second side 22 of the single electrode foil 2. In some embodiments, for example, as shown, the double-sided electrode includes two graded metal alloy layers 4a, 4b on each side of the current collector 2, i.e., one graded layer 4b between the negative electrode metal layer 3 and the current collector 2, and another graded layer 4b along the face of the negative electrode metal layer 3 opposite the current collector 2. The color gradient in the layers 4a and 4b indicates that the concentration of the negative electrode metal (preferably Li) decreases from the negative electrode metal layer 3 outward.

[0064] Of course, the double-sided electrode can be implemented differently, for example, according to Figure 1B , 1Cand one or more arrangements discussed in 2A. Similarly, it is understood that the graded metal alloy layer of the double-sided electrode can be based on Figure 2C One or more of the continuous and / or step gradients described in .

[0065] Figure 3B A cross-sectional side view of an electrode 1 is provided, wherein the current collector 2 is a 3D structured current collector comprising a plurality of conductive protrusions 2p. These protrusions extend from a base 2b (eg, the top surface of a foil) and are covered by a negative electrode metal layer 3 and a graded metal alloy layer 4.

[0066] The height and spacing of these protrusions are usually limited by the ability to provide conformal coverage of the graded metal alloy layer or the cathode metal layer, respectively. In general, the aspect ratio (AR) (height / width) of the gaps between these pillars is usually ≤ 50. When physical vapor deposition (PVD) is used to deposit the layers, conformal coverage can be achieved for AR ≤ 5. When electrodeposition is used, the upper limit can be higher, such as ≤ 50. For sputtering deposition and electron gun evaporation, the aspect ratio is usually ≤ 5. With so-called ionized sputtering, conformal coverage can be achieved for AR ≤ 10.

[0067] Figure 3C An exploded cross-sectional side view of a secondary lithium metal battery 100 including an electrode 1 as disclosed herein is provided. The secondary lithium metal battery 100 also includes at least one separator 6 and a counter electrode 7. It is known that the separator provides negative electrode metal ion transport between the opposing electrodes during battery operation. Therefore, the separator generally comprises a salt composition comprising ions of the negative electrode metal (e.g., Li + ). In addition, the battery may include one or more additives, such as a negative electrode solution and / or a positive electrode solution, to reduce the interfacial resistance of the negative electrode side and the positive electrode side of the separator, respectively.

[0068] In a preferred embodiment, for example, Figure 3CAs shown, the counter electrode 7 of the battery includes a layer of a positive electrode composition 8. The positive electrode composition includes negative electrode metal ions, such as lithium ions. The negative electrode metal ions can be used to plate the negative electrode metal (e.g., Li metal) onto the negative electrode (e.g., in the initial charging cycle), for example, onto one or more seed layers (graded metal alloy layer 4b) and the negative electrode metal layer 3. When the negative electrode metal is lithium, such a battery is generally referred to as a secondary lithium metal battery (LMB). The amount of negative electrode metal contained in the positive electrode can substantially define the total negative electrode metal inventory (capacity) of the secondary battery 100. As discussed above, before the initial charge, the amount of metal contained in the negative electrode metal can advantageously provide a buffering amount to replace the loss of negative electrode metal during the long-term cycling of the battery. For embodiments including a positive electrode composition that substantially defines the total negative electrode metal inventory (capacity) of the secondary battery, the thickness of the negative electrode metal layer (before the initial charge) is preferably < 20 μm.

[0069] In another embodiment, the battery is configured as a lithium-air (Li-air) or lithium-sulfur (Li-S) battery. It should be understood that for Li-air and Li-S batteries, a positive electrode composition containing negative electrode metal ions is not required. Instead, the redox reaction of lithium metal is balanced with respect to air and sulfur-containing compositions, respectively. Therefore, the total active negative electrode metal inventory can be defined by the negative electrode metal layer provided to the electrode 1 before the initial operation of the battery. In order to achieve commercially relevant capacity, the thickness of the negative electrode metal layer 3 is generally ≥ 5 μm, preferably greater, for example, ≥ 20 μm or greater, for example, up to 50 μm or 100 μm.

[0070] Generally speaking, a method 200 for manufacturing an electrode 1 for a secondary lithium metal battery 100 includes at least the following steps: providing 201 a current collector; depositing 202 a lithium-containing negative electrode metal component into layers, and one or more steps of depositing 203 a graded metal alloy layer comprising a mixture of lithium and another metal component, wherein the concentration of lithium relative to the other metal component decreases from the negative electrode metal layer outward. The order of steps 202 and 203 can vary depending on the position of the graded metal alloy layer 4 relative to the negative electrode metal layer 3 (i.e., above, below, or on both sides). In some embodiments, the graded metal alloy layer is deposited on top of (after) the negative electrode metal layer, for example, Figure 4B In other embodiments, one or more graded metal alloy layers are deposited before depositing the cathode metal layer, for example, Figure 4A Optionally, after assembling the electrodes in the battery system, part or all of the negative electrode metal layer 3 may be provided, for example, Figure 3C In some embodiments, for example, Figure 4C and 4D As shown, the graded metal alloy layer 4 is deposited before and after the cathode metal layer 3 is deposited.

[0071] Depositing 203 the graded metal alloy layer includes co-depositing lithium and another metal component. It has been found that co-deposition, that is, the deposition of the negative electrode metal component and one or more other metals together, is a suitable method for providing a layer having a graded composition (e.g., a gradual and / or layer-by-layer concentration gradient) disclosed herein. Co-deposition can include one or more of vapor deposition and electrodeposition of the corresponding components (e.g., lithium and another metal component) by one or more suitable processes. Suitable methods include chemical and physical vapor deposition and electroplating. By providing appropriate time changes (during the deposition period), for example, changing the concentration or deposition conditions, a gradual and / or step-like gradient can be obtained. Alternatively, or in addition, each gradient can also be obtained by processing the electrode at multiple stations separated in space or temperature, each of which is configured to provide a layer of a specific thickness at a given concentration.

[0072] Thus, in some embodiments, for example, Figure 4B As shown, the method includes repeatedly performing the step of depositing a graded metal alloy layer (e.g., n times) to form the graded metal alloy layer into a multilayer stack including a plurality of subsequently deposited sublayers (n layers), whereby the lithium concentration in the subsequent sublayers of the stack decreases in a direction starting from the first sublayer on the negative electrode metal layer (see Figure 2B Layers 4-1, 4-2, 4-n).

[0073] Advantageously, the electrodes and methods as disclosed herein are particularly suitable for large-scale production, for example, by continuous production methods such as roll-to-roll (R2R) processing.

[0074] Figure 4D An embodiment of an R2R production process configured to provide a double-sided electrode 1 is shown, wherein the negative electrode layer is sandwiched between respective graded metal alloy layers 4a, 4b along both faces of a current collector 2. Thus, in some embodiments, the current collector is an elongated metal foil or metal-coated polymer foil, and wherein the steps of depositing the negative electrode metal component and the graded metal alloy layer (including sublayers if present) are configured as a roll-to-roll process.

[0075] For the purpose of clear and concise description, each feature is described herein as part of the same or independent embodiment, however, it should be understood that the scope of the present invention may include embodiments having a combination of all or some of the described features. Of course, it should be understood that any of the above embodiments or process methods can be combined with one or more other embodiments or process methods to provide further improvements in finding and matching designs and advantages.

[0076] In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or actions than those listed in a given claim; the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; several "measures" may be represented by the same or different items or implemented structures or functions; unless otherwise specifically stated, any disclosed device or part thereof may be combined together or separated into other parts. When one claim refers to another claim, this may mean that synergistic advantages are achieved through the combination of their respective features. However, the fact that certain measures are cited in mutually different claims does not mean that the combination of these measures cannot also be advantageous. Therefore, the various embodiments of the present invention may include all valid combinations of the claims, wherein each claim may in principle refer to any preceding claim unless the context clearly excludes it.

Claims

1. An electrode (1) for a secondary lithium metal battery (100), the electrode comprising: Current collector (2), a negative electrode metal layer (3) comprising lithium, and At least one graded metal alloy layer (4), the graded metal alloy layer extending along one or more opposite faces of the negative electrode metal layer, the graded metal alloy layer comprising a mixture of lithium and another metal component other than Li, wherein the concentration of lithium relative to the another metal component decreases from the negative electrode metal layer outward.

2. The electrode according to claim 1, wherein The concentration of lithium relative to the other metal component decreases from the negative electrode metal layer outward across the graded metal alloy layer (4).

3. The electrode according to claim 1 or 2, wherein The negative electrode metal layer (3) overlaps a portion of the graded metal alloy layer (4).

4. An electrode according to any one of the preceding claims, wherein The graded metal alloy layer (4) is a multilayer stack (4s) having a plurality of sublayers (4-1, 4-2, 4-n), whereby the concentration of lithium relative to the other metal component in subsequent sublayers (4-2, 4-n) of the stack decreases starting from the first sublayer (4-1) on the negative electrode metal layer (3).

5. An electrode according to any one of the preceding claims, wherein The graded metal alloy layer (4) is disposed between the current collector (2) and the negative electrode metal layer (3), wherein the relative concentration of lithium in the mixture increases in a direction away from the current collector, preferably increasing to 100% at the interface with the negative electrode metal layer (3).

6. An electrode according to any one of the preceding claims 1 to 4, wherein The graded metal alloy layer (4) is arranged along the surface of the negative electrode metal layer (3) relative to the current collector to engage with the separator (6), and the relative concentration of lithium in the mixture decreases in a direction away from the negative electrode metal layer, preferably substantially to 0 vol%.

7. An electrode according to any one of the preceding claims, wherein The electrode comprises one of the graded metal alloy layer of claim 5 and another graded metal alloy layer of claim 6 .

8. An electrode according to any one of the preceding claims, wherein The concentration of lithium in the graded metal alloy layer (4) decreases from substantially 100% relative to the other metal component at the negative electrode metal layer to substantially 0% across the graded metal alloy layer (4).

9. An electrode according to any one of the preceding claims, wherein The other metal component includes one or more of indium (In), zinc (Zn), magnesium (Mg), bismuth (Bi) and / or tin (Sn), preferably indium.

10. An electrode according to any one of the preceding claims, wherein The current collector (2) comprises a metal foil or a metal-coated polymer foil, preferably comprising copper (Cu), nickel (Ni), or a composite material comprising one or more thereof.

11. An electrode according to any one of the preceding claims, wherein The graded metal alloy layer (4) has a thickness (t4) in the range of 5-500 nm.

12. An electrode according to any one of the preceding claims, wherein The current collector (2) is a structured current collector, comprising a plurality of conductive protrusions (2p) extending from a substrate (2b) and covered by the negative electrode metal layer (3) and the graded metal alloy layer (4).

13. An electrode according to any preceding claim, comprising respective said cathode metal layer (3) and said at least one graded metal alloy layer (4) on opposite sides of a common current collector (2).

14. A secondary battery (100) comprising the electrode (1) according to any one of the preceding claims as a negative electrode, a separator (6) and a counter electrode (7).

15. The secondary battery system according to claim 14, comprising a layer of a positive electrode composition (8) loaded with lithium ions, and wherein the negative electrode metal layer (3) has a thickness (t3) in the range of < 20 μm.

16. The secondary battery according to claim 14 or 15, wherein: The battery is configured as a lithium-air or lithium-sulfur battery, and wherein the negative electrode metal layer has a thickness (t3) of ≥ 5 μm.

17. A method (200) for manufacturing an electrode (1) for a secondary lithium metal battery (100), the method comprising: providing (201) a current collector, depositing (202) a negative electrode metal component including lithium as a layer, and one or more steps of depositing (203) a graded metal alloy layer comprising a mixture of lithium and another metal component, wherein the concentration of lithium relative to the other metal component decreases from the negative electrode metal layer outward, Wherein depositing (203) the graded metal alloy layer comprises co-depositing lithium and the other metal component.

18. The method according to claim 17, wherein: Co-depositing lithium and the other metal component includes one or more of vapor deposition and electrodeposition.

19. The method according to claim 17 or 18 includes repeatedly depositing the graded metal alloy layer to form the graded metal alloy layer into a multilayer stack comprising a plurality of subsequently deposited sublayers, whereby the lithium concentration in subsequent sublayers of the stack decreases in a direction starting from the first sublayer at the negative electrode metal layer.

20. The method according to any one of claims 17 to 19, wherein: The current collector is an elongated metal foil or a metal coated polymer foil, and wherein the step of depositing the negative electrode metal component and the graded metal alloy layer including sublayers if present is configured as a roll-to-roll process.

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