Electrode, battery, and method having an inclined alloy layer

Abstract

The present disclosure relates to an electrode (1) for a secondary lithium metal battery. The electrode comprises a current collector (2), a lithium-containing anode metal layer (3), and at least one inclined metal alloy layer (4a, 4b) extending along one or both sides of the anode metal layer. The inclined metal alloy layer contains a mixture of lithium and a further metal composition, and the concentration of lithium relative to the further metal composition decreases outward from the anode metal layer. Furthermore, the present disclosure relates to a battery comprising the electrode and a manufacturing method.

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 such an electrode.

Background Art

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

[0003] During charging, Li ions move from the cathode through the electrolyte to the anode and deposit as Li metal (Li 0 ). During discharging, Li ions return to the cathode. However, during the plating / stripping cycle, the battery suffers from lithium loss due to the detrimental reaction of lithium with the electrolyte and / or the formation of porous or dendritic lithium deposits, which further increases the risk of short circuit and decreases the operating life and performance of the battery.

[0004] J. Lou et al. ("Nanomaterials 11, 300", 2021) describe a LiSn alloy anode composition that suppresses the growth of lithium dendrites. However, this layer is composed of only a single overall composition of a relatively large amount of inappropriate or suboptimal Li conductive material, which can be regarded as a dead weight from the perspective of electrical efficiency and does not participate in the battery reaction. Furthermore, its chemo-mechanical stability remains room for improvement in terms of both the mechanical expansion coefficient and the electric field lines across the intermediate layer.

[0005] C. Zhong et al. ("Materials Today Energy 18, 100528", 2020) describe various multi-element Sn-Co-Sb alloy anodes for retaining Li with different ratios of Sn:Co:Sb. These alloy compositions are manufactured by tilting the substrate. Therefore, these alloy compositions are not homogeneous across the horizontal subplane parallel to the substrate. As a result, in the vertical direction, the composition varies from local spot to local spot and consists of a relatively large amount of inappropriate or suboptimal Li-conductive material (a dead weight from the perspective of electrical efficiency) that does not participate in the battery reaction.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present disclosure aims to resolve or at least mitigate one or more of the above-mentioned drawbacks by providing an electrode, a method, and a battery as disclosed herein.

[0008] Furthermore, the present invention aims to provide a battery with improved performance and / or lifespan by reducing one or more of the harmful reactions of the anode metal during manufacturing and / or the harmful volume and surface changes due to the repetition of Li insertion and extraction during battery cycles, particularly the initial charge cycle. As will be described in more detail hereinafter, the electrodes as disclosed herein can advantageously contribute to one or more of the above objectives.

Means for Solving the Problems

[0009] According to a first aspect, an electrode, particularly an electrode for a secondary lithium metal battery, is provided. The electrode comprises at least a current collector and an anode metal layer extending along one or more surfaces of the current collector. The anode metal layer typically comprises at least a battery active metal composition that is at least or substantially lithium metal. Optionally, the active metal composition can include other battery active metals such as (alkaline earth) alkali metals such as K, Na, and Ca. The anode metal layer comprises at least one gradient metal alloy layer. The gradient metal alloy preferably extends along one or both sides of the anode metal layer substantially conformally.

[0010] Depending on the position of the gradient metal alloy layer, this layer can be understood as a cover layer provided along the surface of the anode metal layer located on the opposite side of the current collector, or as an intermediate layer extending between the anode metal layer and the current collector.

[0011] The inclined metal alloy layer typically comprises a mixture of a battery active metal composition, which is typically lithium metal, and a further metal composition other than the active metal composition. This further metal composition can include one or more other metals (typically other than lithium) that alloy with the battery active metal composition. Typically, these metals are selected to have at least a lower redox potential than the active anode active composition of the battery. The abundance (e.g., volume % concentration) of lithium (the battery active metal) relative to this further metal composition decreases in a direction away from the interface with the anode metal layer. In a direction orthogonal to this (along the interface with the anode metal layer), the relative abundance of the metals in the mixture is preferably constant.

[0012] The concentration of lithium (the anode active metal) relative to the further metal composition gradually decreases from a maximum value (e.g., 100%) at the interface with the anode metal layer to a minimum value (e.g., 0%) at the interface located on the side beyond the thickness of the inclined metal alloy layer.

[0013] Alternatively or additionally, the concentration of lithium decreases stepwise from the surface located in the anode layer. Thus, in some preferred embodiments, the inclined metal alloy layer can be formed as a multilayer stack comprising a plurality of sub-layers, and the concentration of lithium metal (the anode metal) relative to the further metal composition in subsequent sub-layers of the stack decreases in a direction away from the anode metal layer. Therefore, the inclined metal alloy layer and / or the anode metal layer may be understood to form a laminate such as, for example, a nanolaminate.

[0014] While not desiring to be bound by theory, the inventors have discovered that the advantages of providing a gradient layer comprising a mixture of a battery active metal composition, typically lithium, and a further metal composition other than the active metal composition, are related to the formation of layers having anisotropic volume expansion. This is thought to suppress volume and surface changes due to repeated insertion and extraction of anode metal (e.g., lithium) during battery cycling, particularly during the first cycle and / or the first plurality of cycles, and thus prevent the gradual degradation of the metal anode layer.

[0015] Depending on the position below and / or above the anode metal layer, the gradient metal alloy layer may provide the function of a passivation layer and / or a seed layer.

[0016] It has been found that by imparting a gradient composition to the metal alloy layer throughout its thickness, the total amount of material (further metal composition) that does not participate in the battery reaction can be advantageously reduced without affecting the beneficial properties as described herein.

[0017] As will be described in more detail hereinafter, advantageously, the gradient metal alloy layer can relax heterogeneous anode metal plating as a seed layer (particularly during the initial charge cycle and / or subsequent charge operations during battery operation). Further, this seed layer may enable homogeneous anode metal stripping during battery discharge operation. Advantageously, the combination of these effects contributes to improving the performance, durability, and / or safety of the battery by relaxing the formation of isolated anode metal domains (so-called mossy domain structures) and / or by relaxing the formation or propagation of so-called dendrites.

[0018] When formed as a passivation layer, advantageously, this gradient metal alloy layer results in a loss of the battery's active material, particularly during battery assembly and / or electrode storage, due to the atmosphere (O 2 , CO 2 , and / or N 2The deterioration of the anode metal, such as harmful reactions caused by exposure to (0), can be alleviated.

[0019] Thus, in some preferred embodiments, the gradient metal alloy layer is formed between the current collector and the anode metal layer, i.e., as an interfacial layer between the current collector and the anode metal layer, and the relative concentration of lithium in the mixture increases to 100% in the direction away from the current collector, preferably at the interface with the anode metal layer.

[0020] Thus, in some other or further preferred embodiments, the gradient metal alloy layer is formed along the surface of the anode metal layer located on the opposite side of the current collector, i.e., along the outer surface of the electrode located on the opposite side of the current collector for bonding with the separator of the battery system, and the relative concentration of lithium in the mixture decreases in the direction away from the anode metal layer, preferably to substantially 0% by volume. The greater the relative amount of the additional anode metal towards the outer interface, the better the protection of the underlying anode metal (e.g., Li) against harmful reactions with the atmosphere.

[0021] In a more preferred embodiment, the electrode comprises one of these gradient metal alloy layers along both surfaces of the anode metal layer, i.e., one gradient metal alloy layer along the interface between the current collector and the anode metal layer, and further comprises an additional gradient metal alloy layer along the outer surface of the electrode located on the opposite side of the current collector. The composition of the additional metal composition in each of these gradient layers may be the same, but it is not necessary to be the same. For example, the additional metal composition contained in the lower (seed) layer may be selected to optimize the electrical contact with the current collector and achieve optimal wettability of the subsequent anode metal layer, while the additional metal composition contained in the upper (passivation) layer may be selected to be aggressive towards the anode metal or anode metal ions (e.g., Li metal / ions) while minimizing the reactivity with the atmosphere.

[0022] According to another or further aspect, a secondary battery comprising an electrode as disclosed herein is provided. Further, the battery comprises a separator and a counter electrode. The separator typically includes an electrolyte composition such as, for example, a solid, semi-solid, or liquid electrolyte composition. Further, the battery can include one or more of an anode liquid composition and / or a cathode liquid composition. The anode metal layer included in the electrode comprises at least one graded metal alloy layer (above, below, or on both sides). Advantageously, the graded metal alloy layer provides the battery with the advantages described with respect to passivation, seeding, or both passivation and seeding, depending on its position.

[0023] In some embodiments, the battery is configured as a secondary anode metal battery, typically a secondary lithium metal battery (LMB), and the counter electrode comprises a layer of cathode composition filled with anode metal cations (lithium ions in the case of an LMB). In a preferred embodiment, the anode metal layer has a thickness within the range of <20 μm prior to the initial charge cycle of the battery. The amount of anode metal (lithium in the case of an LMB) thus provided has been found to provide an effective buffer to compensate for losses that occur depending on the total amount of active anode metal provided by the cathode composition during the progression of the battery cycle.

[0024] In other embodiments, the total amount of active anode metal can be determined by the initial amount of anode metal contained in the anode metal layer (i.e., the amount prior to the initial battery cycle). For example, in one embodiment, the battery is configured as a secondary lithium-air battery. In another embodiment, the electrode is used in the assembly of a secondary lithium-sulfur battery (Li-S).

[0025] In any case, preferably, the amount of anode metal is the areal capacity of the battery (mAh / cm 2) is in an amount such that it is ≧1, preferably ≧4. Regarding the thickness, the anode metal layer preferably has a thickness of ≧5 μm, more preferably a thickness of ≧20 μm or more, and has a thickness such as up to 50 μm or 100 μm, for example. When the anode metal layer (e.g., Li) is dispersed on the 3D structure anode, its thickness can be appropriately adjusted.

[0026] According to yet another or other aspect, a method of manufacturing an electrode as described herein is provided. This method includes the steps of preparing a current collector, depositing an anode metal composition containing lithium as a layer, and one or more steps of depositing a gradient metal alloy layer containing a mixture of lithium and a further metal composition, wherein the concentration of lithium with respect to the further metal composition decreases outward from the anode metal layer. The step of depositing the gradient metal alloy layer generally includes the step of co-depositing lithium (or another anode metal composition) and a further metal composition.

[0027] In a preferred embodiment, the step of co-depositing includes one or more of vapor deposition and electrochemical deposition.

[0028] In another or further preferred embodiment, this method is a step of forming a gradient metal alloy layer as a multi-layer stack comprising a plurality of subsequently deposited sub-layers by repeatedly performing the step of depositing a gradient metal alloy layer containing a mixture of lithium and a further metal composition, wherein the concentration of lithium in the subsequent sub-layers of the stack decreases in one direction from the first sub-layer in the anode metal layer.

[0029] In other or further preferred embodiments, preferably the current collector is a flexible elongated foil such as a metal foil or a metal-coated foil. Advantageously, this method is for performing the step of depositing the anode metal composition and the step of depositing the gradient metal alloy layer (if present, comprising sub-layers) in, for example, a well-regulated inert atmosphere (e.g., moisture, oxygen, CO2 and / or N 2 It can be configured as a roll-to-roll process that includes passing the current collector through each spatially separated station, such as a station within (e.g., substantially absent of)

[0030] These and other features, aspects, and advantages of the devices, systems, and methods of the present disclosure will be better understood from the following description, the appended claims, and the accompanying drawings.

Brief Description of the Drawings

[0031]

Figure 1A

Figure 1B

Figure 1C

Figure 2A

Figure 2B

Figure 2C

Figure 3A

Figure 3B

Figure 3C

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Best Mode for Carrying Out the Invention

[0032] The terms used to describe specific embodiments are not intended to limit the present invention. In this specification, the articles "a," "an," and "the" are intended to include the plural as well as the singular, unless the context clearly dictates otherwise. The phrase "and / or" includes any and all combinations of one or more of the associated listed items. The terms "comprises" and / or "comprising" are understood to specify the presence of the stated features, but do not preclude the presence or addition of one or more other features. Further, when a particular step of a method is indicated as following another step, unless otherwise indicated, that step can follow immediately after the other step, or one or more intermediate steps may be performed before that particular step is carried out. Similarly, when a connection between structures or components is described, unless otherwise indicated, this connection may be established directly, or through intermediate structures or components.

[0033] Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings in which the embodiments of the invention are illustrated. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-sectional views of idealized embodiments and intermediate structures in some cases of the present invention. In this description and the drawings, like numerals indicate like elements throughout. Relative terms and their derivatives are to be construed to indicate the orientation shown in the drawings in the context of the orientation being described or discussed. These relative terms are for convenience of description and do not require the system to be constructed or operated in a particular orientation unless otherwise specified.

[0034] Next, electrode 1 will be described in more detail with reference to FIGS. 1 to 3B. As will be further described with reference to FIG. 3C, this electrode can be particularly beneficial in the assembly of a secondary anode metal battery.

[0035] For example, electrode 1 as shown in FIGS. 1B, 1C, 2A, 2B, 3A, and 3B includes a current collector 2, an anode metal layer 3, and at least one gradient metal alloy layer 4, 4a, 4b. This anode metal layer 3 contains or is mainly composed of one or more elements selected from Na, K, Mg, and / or Ca, and preferably contains Li or is mainly composed of Li. The gradient metal alloy layer contains a mixture of one or more elements (preferably lithium) contained in the anode metal layer 3 and a further metal composition containing one or more other elements alloyed with the anode metal.

[0036] As shown in FIG. 1A, the gradient metal alloy layer 4 extends as a conformal layer along one or both of the two surfaces 31, 32 of the anode metal layer 3.

[0037] As will be described in more detail with reference to FIG. 2C, the concentration (in vol%) or relative abundance of the anode active material (e.g., Li) with respect to the other metal composition decreases outward from the interface between the anode metal layer 3 and the gradient metal alloy layer 4.

[0038] Generally, the thickness t3 of the anode metal layer, the thicknesses t4, t4a, t4b of the gradient metal alloy layer, and the positions of the anode metal layer 3 and the gradient metal alloy layer 4 with respect to the current collector 2 are determined by the intended use of the electrode, for example, by the type of battery system in which the electrode is used.

[0039] In one embodiment, such as that shown in FIG. 1B for example, the anode metal layer 3 is provided as an intermediate layer extending between the current collector 2 and the inclined metal alloy layer 4a. Therefore, the inclined metal alloy layer 4a can be understood to form a cover layer facing the atmosphere before being assembled into the battery. Therefore, the inclined metal alloy layer 4a forms a protective layer, i.e., a passivation layer, which alleviates the harmful reaction (deterioration) of the underlying anode metal layer 3, such as by exposure to the atmosphere before and / or during assembly into the battery system.

[0040] In another or further embodiment, such as that shown in FIG. 1C for example, the inclined metal alloy layer 4b is provided as an intermediate layer between the current collector 2 and the anode metal layer 3. Therefore, the inclined metal alloy layer 4b can be understood to form a seeding layer for receiving a layer of the anode metal composition, such as by deposition before assembly into the battery system, and / or as part of a plating path or charging path of the assembled battery system (as shown in FIG. 3C for example).

[0041] In yet further other embodiments, such as those shown in FIGS. 2A, 3A, and 3C for example, the electrode 1 comprises a first inclined metal alloy layer 4a and a second inclined metal alloy layer 4b, where one layer forms a seed layer 4b provided as an intermediate layer between the current collector 2 and the anode metal layer 3, and the other layer forms a passivation layer provided along the surface of the anode metal layer 3 located on the opposite side of the seed layer.

[0042] The further metal composition mentioned above contains one or more elements selected from zinc, magnesium, and / or metals or metalloid elements of Groups 13-15, preferably including 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 (the decrease in slope during battery cycling) is that the resulting alloy has relatively little volume expansion, and the less the volume expansion, the more preferable. Therefore, preferably, this further metal composition contains one or more of indium (In), zinc (Zn), magnesium (Mg), bismuth (Bi), and / or tin (Sn), and most preferably contains tin.

[0043] Ternary alloys (e.g., Li-Cu-Sn), quaternary alloys (e.g., Li-Al-O-N), or alloys of four or more elements are possible. In this regard, refer to the compositions disclosed in the publication "Adv. Sci. 1600517" (2017) by Y. Zhu et al. This publication is incorporated herein by reference.

[0044] Preferably, the current collector comprises or mainly consists of a metal foil or a polymer foil coated with a metal, preferably a metal foil or a polymer foil coated with a metal that comprises a composite material containing copper (Cu), nickel (Ni), or one or more of them and comprises or mainly consists of them.

[0045] In some embodiments, the current collector may be a so-called 3D current collector or a composite 3D current collector comprising a plurality of high aspect ratio conductive scaffold elements oriented away from the foil (e.g., in a substantially normal direction). For example, the conductive scaffold elements can comprise vertically aligned carbon nanotubes, such as an array of pillars grown from a catalyst seed on a Cu foil. Therefore, in some embodiments, the electrode comprises a structured current collector comprising a plurality of conductive protrusions extending from a base and covered by an anode metal layer and an inclined metal alloy layer.

[0046] In some embodiments, the inclined metal alloy layer has a thickness t4, t4a, t4b in the range of 5 to 500 nm. For the seed layer, the thickness t4b is preferably in the range of 5 to 25 nm. It has been found that a seed layer having a thickness within this range enables efficient relaxation of volume expansion and seed film formation while minimizing the content of the inert metal.

[0047] When the inclined metal alloy layer is provided along the surface of the anode metal layer for bonding to the separator of the battery (as a passivation layer or a protective layer), a thickness t4a of about 50 to 100 nm can realize effective relaxation of volume expansion during cycling and shielding from the atmosphere while minimizing the content of the inert metal.

[0048] Similarly, the thickness of the anode metal layer t3 is determined by the intended use. In principle, this thickness can range from infinitesimal to a maximum of about 20 μm or more. Note that in some embodiments, the anode metal layer may be part of a portion of the inclined metal alloy layer, such as the outermost sublayer, or may overlap this portion.

[0049] In other or further embodiments, the anode metal layer can be specified as a layer having a thickness typically ≦20 μm depending on the amount of the specified anode metal. The amount of the anode metal used can be understood as a buffer amount for compensating for the anode metal loss from the total amount of the anode metal as defined, for example, by the cathode composition during battery operation. For example, in an electrode configured to be assembled into an anode metal - air battery (such as a lithium - air battery) or an anode metal - sulfur battery (such as a lithium - sulfur battery), in still other or further embodiments, the anode metal layer can be specified as a layer having a thickness typically ≧5 μm depending on the total amount of the anode metal (such as lithium) of the system.

[0050] In some embodiments, such as those shown in FIG. 2C (right), for example, the concentration of lithium (anode active metal) with respect to the additional metal composition gradually decreases from a maximum value (e.g., 100%) at the interface with the anode metal layer to a minimum value (e.g., 0%) at the interface located beyond the thickness of the gradient metal alloy layer.

[0051] Of course, it is not necessarily required that the concentration of the anode active metal with respect to the additional metal composition ranges from about 100 percent in the anode metal layer 3 to about 0 percent at the interface located on the opposite side beyond the gradient metal alloy layer 4. Other ranges are also expected, such as ranges having an upper limit of about 90, 80, or 70% and / or a lower limit of about 10, 20, or 30%, for example, ranges 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% are expected.

[0052] However, for the passivation layer, in order to reduce harmful reactions with the atmosphere, such as with lithium, it is highly preferred that the concentration of the anode active metal (e.g., Li) decreases to about 0 percent.

[0053] In some preferred embodiments, such as those shown in FIGS. 2B and 2C (left), for example, the gradient metal alloy layer 4 is formed as a multilayer stack 4s comprising a plurality of sub - layers 4 - 1, 4 - 2, 4 - 3, 4 - n, and the concentration of lithium with respect to the additional metal composition in subsequent sub - layers 4 - 2, 4 - 3, 4 - n of this stack decreases from the first sub - layer 4 - 1 at the position of the anode metal layer 3.

[0054] Forming the inclined metal alloy layer and / or the anode metal layer as a laminate has been found to provide advantages in terms of uniformity across the manufacturing batch and reduction of manufacturing complexity. As will be described in more detail with reference to Figure 4D, the (nano)laminate can be formed particularly effectively by a continuous manufacturing process such as, for example, a roll-to-roll (R2R) process, and subsequent sub-layers are formed in a spatially separated and preferably air-excluded processing unit (such as, for example, an R2R manufacturing line comprising a plurality of deposition units that can be individually configured to deposit a particular mixture of particular sub-layers).

[0055] Alternatively or additionally, a continuous or at least semi-continuous gradient, such as, for example, that shown in Figure 2C (left), can be achieved by one or more processing units, such as, for example, a deposition station, configured to perform a temporal adjustment of the deposition parameters.

[0056] Advantageously, this electrode can be implemented as a double-sided electrode. For example, this can be implemented by forming an anode metal layer and at least one inclined metal alloy layer as disclosed herein along two surfaces (front and back) located on both sides of a common current collector. Alternatively, the double-sided electrode can be provided by positioning two single-sided electrodes back-to-back. Advantageously, the double-sided electrode can be used in the manufacture and assembly of a battery with improved energy density by forming an integrated electrode stack.

[0057] FIG. 3A shows an embodiment of a double-sided electrode 1 comprising a first layer of an anode metal layer and at least one inclined metal alloy layer as disclosed herein along a first surface 21 of a single electrode foil 2, and a second layer of an anode metal layer and at least one inclined metal alloy layer as disclosed herein along a second surface 22 of the single electrode foil 2. In some embodiments as illustrated, for example, the double-sided electrode comprises two inclined metal alloy layers 4a, 4b on respective surfaces of the current collector 2, i.e., one inclined layer 4b located between the anode metal layer 3 and the current collector 2, and another inclined layer 4b along the surface of the anode metal layer 3 located on the opposite side of the current collector 2. The color gradation of the layers 4a and 4b indicates that the concentration of the anode metal (preferably Li) decreases outward from the anode metal layer 3.

[0058] Of course, the double-sided electrode may be implemented in different manners according to, for example, one or more of the configurations discussed in connection with FIGS. 1B, 1C, and 2A. Similarly, it will be understood that the inclined metal alloy layers of the double-sided electrode may be implemented according to one or more of the continuous gradients and / or stepped gradients described in connection with FIG. 2C.

[0059] FIG. 3B shows a side cross-sectional view of the electrode 1, where the current collector 2 is a current collector having a 3D structure including a plurality of conductive protrusions 2p. These protrusions extend from a base 2b, such as the upper surface of the foil, and are covered by the anode metal layer 3 and the inclined metal alloy layer 4.

[0060] The height and spacing of these protrusions are generally limited by the ability to conformally coat the inclined metal alloy layer, i.e., to form the anode metal layer. Typically, the aspect ratio (AR) (height / width) of the spacing between pillars is generally ≦50. When physical vapor deposition (PVD) is used to deposit each layer, conformal coating is achieved when AR≦5. When electrodeposition is used, the upper limit may be even higher, e.g., ≦50. In the case of sputter deposition and electron gun sputtering, the aspect ratio is typically ≦5. In so-called ionized sputtering, conformal coating can be obtained when AR≦10.

[0061] FIG. 3C shows a side exploded cross-sectional view of a secondary lithium metal battery 100 including an electrode 1 as disclosed herein. The secondary lithium metal battery 100 further includes at least a separator 6 and a counter electrode 7. As is known, this separator is provided to transport anode metal ions between electrodes located opposite each other during operation of the battery. For this reason, the separator typically includes a salt composition containing ions of the anode metal (e.g., Li+). Further, the battery can include one or more additives such as an anode liquid and / or a cathode liquid to reduce the interfacial resistance on each of the anode side and the cathode side of the separator.

[0062] In a preferred embodiment, such as that shown in FIG. 3C for example, the counter electrode 7 of the battery comprises a layer of the cathode composition 8. This cathode composition contains anode metal ions such as, for example, lithium ions. The anode metal ions can be used to plate an anode metal (e.g., Li metal) onto the anode, for example, onto one or more of the seed layer (the inclined metal alloy layer 4b) and the anode metal layer 3 (e.g., in the initial charge cycle). When the anode metal is lithium, such a battery is commonly referred to as a secondary lithium metal battery (LMB). The amount of anode metal contained in the cathode can substantially define the total amount (capacity) of anode metal of the secondary battery 100. Advantageously, as discussed above, the amount of metal contained in the anode metal prior to initial charging can provide a buffer amount to compensate for anode metal loss during long-term battery cycling. In embodiments including a cathode composition that substantially defines the total amount (capacity) of anode metal of the secondary battery, the thickness of the anode metal layer (prior to initial charging) is preferably <20 μm.

[0063] In another embodiment, the battery is configured as a lithium-air (Li-air) battery or a lithium-sulfur (Li-S) battery. It will be appreciated that in the case of Li-Air and Li-S batteries, a cathode composition containing anode metal ions is not required. Instead, the redox reaction of the lithium metal is balanced with respect to each of the compositions containing air and sulfur. Thus, the total amount of active anode metal can be defined by the anode metal layer provided on the electrode 1 prior to the initial operation of the battery. To enable a commercially significant capacity, the thickness of the anode metal layer 3 is typically ≧5 μm, preferably more, for example ≧20 μm or more, for example up to 50 μm or 100 μm at most.

[0064] Generally, a method 200 for manufacturing an electrode 1 for a secondary lithium metal battery 100 includes at least a step 201 of forming a current collector, a step 202 of depositing a lithium-containing anode metal composition as a layer, and one or more steps 203 of depositing a gradient metal alloy layer including a mixture of lithium and a further metal composition, wherein the concentration of lithium with respect to the further metal composition decreases outward from the anode metal layer. The order of steps 202 and 203 can be changed according to the position (i.e., above, below, or both) of the gradient metal alloy layer 4 with respect to the anode metal layer 3. In some embodiments, the gradient metal alloy layer is deposited (subsequently) on top of the anode metal layer, as shown, for example, in FIG. 4B. In other embodiments, one or more gradient metal alloy layers are deposited prior to the deposition of the anode metal layer, as shown, for example, in FIG. 4A. Optionally, a part or all of the anode metal layer 3 can be formed after the electrode is incorporated into the battery system, as described, for example, in connection with FIG. 3C. In some embodiments, the gradient metal alloy layer 4 is deposited both before and after the deposition of the anode metal layer 3, as shown, for example, in FIGS. 4C and 4D.

[0065] The step 203 of depositing the graded metal alloy layer includes the co - deposition of lithium and a further metal composition. Co - deposition, i.e., the deposition of both the anode metal composition and one or more further metals, has been found to be a suitable method for forming graded compositions as disclosed herein, for example, layers having a progressive and / or hierarchical concentration gradient. Co - deposition can include one or more of vapor deposition and electrodeposition of each composition (e.g., lithium and the further metal composition) from one or more suitable processes. Suitable processes include chemical vapor deposition, physical vapor deposition, and electrodeposition. Progressive and / or step - like gradients can be achieved, for example, by imparting suitable temporal variations (over the deposition period) that change, for example, concentration or deposition conditions. Alternatively or additionally, the gradient can be obtained by treating the electrodes at a plurality of spatially or thermally separated stations each set to form a layer of a specific thickness at a given concentration.

[0066] Thus, in some embodiments, such as those shown in FIG. 4B for example, the method includes repeatedly performing (e.g., n times) the step of depositing the graded metal alloy layer to form the graded metal alloy layer as a multi - layer stack comprising a plurality of successively deposited sub - layers (n layers), wherein the lithium concentration in the subsequent sub - layers of the stack decreases in one direction from the first sub - layer at the position of the anode metal layer (see layers 4 - 1, 4 - 2, 4 - n in FIG. 2B).

[0067] Advantageously, the electrodes and methods as disclosed herein are particularly suitable for large - scale production, such as by continuous production methods such as roll - to - roll (R2R) processing.

[0068] Figure 4D shows one implementation of an R2R manufacturing method configured to provide a double-sided electrode 1, where the anode layer is sandwiched between corresponding inclined metal alloy layers 4a, 4b along both sides of the current collector 2. Thus, in some embodiments, the current collector is an elongated metal foil or a polymer foil coated with metal, and the steps of depositing the anode metal composition and the inclined metal alloy layer (including sub-layers if present) are configured as a roll-to-roll process.

[0069] In this specification, for purposes of clarity and concise description, features are described as part of the same or different embodiments, but it will be understood that the scope of the invention may include embodiments having combinations of all or some of the described features. Of course, it will be understood that any one of the above-described embodiments or processes may be combined with one or more other embodiments or processes to achieve further improvements in finding consistent designs and advantages.

[0070] In the interpretation of the appended claims, the term "comprising" does not exclude the presence of elements or acts other than those listed in a particular claim, the term "a" preceding an element does not exclude the presence of a plurality of such elements, reference signs in the claims do not limit the claims, a plurality of "means" may be represented by the same or different items or implemented structures or functions, and any of the disclosed devices or parts thereof may be combined together or further separated into other parts as long as there is no specific indication to the contrary. It should be understood that when one claim refers to another claim, this may imply a synergistic advantage achieved by the combination of the respective features of those claims. However, the fact that specific means are described in different claims alone does not indicate that the combination of these means cannot also be used advantageously. Therefore, unless explicitly excluded by the context, the present embodiment may include any effective combination of claims that each claim may in principle refer to any preceding claim as a reference.

Explanation of Reference Signs

[0071] 1 Electrode, double-sided electrode 2 Current collector, single-electrode foil 2b Base 2p Conductive protrusion 3 Anode metal layer 4 Inclined metal alloy layer 4a First inclined metal alloy layer 4b Second inclined metal alloy layer, seed layer 4s Multilayer stack 4-1 First sublayer 4-2 Sublayer 4-3 Sublayer 4-n Sublayer 6 Separator 7 Counter electrode 8 Cathode composition 21 First surface 22 Second surface 31 Surface of anode metal layer Surface of the 32 anode metal layer 100 Secondary lithium metal battery t3 Thickness of the anode metal layer t4 Thickness of the inclined metal alloy layer t4a Thickness of the inclined metal alloy layer t4b Thickness of the inclined metal alloy layer

Claims

1. An electrode (1) for a secondary lithium metal battery (100), comprising: a current collector (2); an anode metal layer (3) containing lithium; and at least one inclined metal alloy layer (4) extending along one or both sides of the anode metal layer, the at least one inclined metal alloy layer (4) containing a mixture of lithium and a further metal composition other than Li, and the concentration of lithium relative to the further metal composition decreasing outward from the anode metal layer. The electrode (1) comprising the above.

2. The electrode according to claim 1, wherein the concentration of lithium relative to the further metal composition decreases outward from the anode metal layer across the inclined metal alloy layer (4).

3. The electrode according to claim 1 or 2, wherein the anode metal layer (3) overlaps a part of the inclined metal alloy layer (4).

4. The inclined metal alloy layer (4) is a multilayer stack (4s) having a plurality of sub-layers (4-1, 4-2, 4-n), and the concentration of lithium relative to the further metal composition in subsequent sub-layers (4-2, 4-n) of the stack decreases from a first sub-layer (4-1) at the position of the anode metal layer (3). The electrode according to any one of claims 1 to 3.

5. The inclined metal alloy layer (4) is provided between the current collector (2) and the anode metal layer (3), and 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 anode metal layer (3). The electrode according to any one of claims 1 to 4.

6. The inclined metal alloy layer (4) is provided along the surface of the anode metal layer (3) located on the opposite side of the current collector for bonding with a separator (6), and the relative concentration of lithium in the mixture decreases in a direction away from the anode metal layer, preferably decreasing to substantially 0% by volume. The electrode according to any one of claims 1 to 4.

7. The electrode according to any one of claims 1 to 6, comprising one of the inclined metal alloy layers according to claim 5 and a further inclined metal alloy layer according to claim 6.

8. The concentration of lithium in the inclined metal alloy layer (4) decreases from substantially 100% with respect to the further metal composition at the position of the anode metal layer to substantially 0% over the inclined metal alloy layer (4). The electrode according to any one of claims 1 to 7.

9. The further metal composition includes one or more of indium (In), zinc (Zn), magnesium (Mg), bismuth (Bi), and / or tin (Sn), preferably including indium. The electrode according to any one of claims 1 to 8.

10. The current collector (2) is composed of a metal foil or a polymer foil coated with a metal, preferably including copper (Cu), nickel (Ni), or a composite material including one or more of them. The electrode according to any one of claims 1 to 9.

11. The inclined metal alloy layer (4) has a thickness (t4) in the range of 5 to 500 nm. The electrode according to any one of claims 1 to 10.

12. The current collector (2) is a structured current collector including a plurality of conductive protrusions (2p) extending from a base (2b) covered by the anode metal layer (3) and the inclined metal alloy layer (4). The electrode according to any one of claims 1 to 11.

13. On both sides of a common current collector (2), one of the anode metal layer (3) and the at least one inclined metal alloy layer (4) is provided respectively. The electrode according to any one of claims 1 to 12.

14. A secondary battery (100) including the electrode (1) according to any one of claims 1 to 13 as an anode, a separator (6), and a counter electrode (7).

15. A layer of a cathode composition (8) filled with lithium ions is provided, and the anode metal layer (3) has a thickness (t3) within the range of <20 μm. The secondary battery system according to claim 14.

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

17. A method (200) for manufacturing an electrode (1) for a secondary lithium metal battery (100), A step (201) of preparing a current collector, A step (202) of depositing an anode metal composition containing lithium as a layer, One or more steps (203) of depositing a gradient metal alloy layer comprising a mixture of lithium and a further metal composition, wherein the concentration of lithium relative to the further metal composition decreases outwardly from the anode metal layer comprising The step (203) of depositing the gradient metal alloy layer comprises a step of co-depositing lithium and the further metal composition. A method (200). **Claim 18** The method according to claim 17, wherein the step of co-depositing lithium and the further metal composition comprises one or more of vapor deposition and electroplating. **Claim 19** A step of forming the gradient metal alloy layer as a multi-layer stack comprising a plurality of successively deposited sub-layers by repeatedly performing the step of depositing the gradient metal alloy layer, wherein the concentration of lithium in subsequent sub-layers of the stack decreases in one direction from a first sub-layer in the anode metal layer. The method according to claim 17 or 18, comprising the step. **Claim 20** The current collector is an elongated metal foil or a polymer foil coated with a metal, and the step of depositing the anode metal composition and the gradient metal alloy layer (comprising the sub-layers if present) is configured as a roll-to-roll process. The method according to any one of claims 17 to 19.

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