Electrodes with a protected carbon-based scaffold

Abstract

This disclosure provides an electrode 1 comprising a 3D composite current collector 2 having a conductive substrate current collector 3 having a plurality of laterally dispersed conductive upright scaffolding elements 4, the carbon-based protrusions 6 covered by a passivation layer 10 for shielding the pillars from direct contact with the electrode or electrolyte material, wherein the passivation layer (10) is composed of a first composition (10c) that enables electron transport to the substrate and is resistant to lithium transport across the passivation layer. In a preferred embodiment, the electrode is coated with a stack of functional battery layers comprising a seed layer 20, an anode metal layer 30, and an anode passivation layer 40. This disclosure further relates to a method for manufacturing the electrode and an energy storage device comprising the electrode.

Description

Technical Field

[0001] The present disclosure relates to electrodes, particularly electrodes comprising a 3D current collector. The present disclosure further relates to energy storage devices and manufacturing methods comprising the electrodes.

Background Art

[0002] Rechargeable lithium-ion battery (LiB) technology is considered a potential technology option for next-generation energy carriers in the global energy shift, such as electrification of transportation and renewable energy storage grids. State-of-the-art LiBs aim to improve the safety issues related to the liquid nature of the electrolyte while improving the current energy density of about 270 Wh / kg at the cell level due to the limited capacity of graphite (370 mAh / g) at the anode. To increase the viability of electric mobility, a combination of higher energy density cells (e.g., >400 Wh / kg) and the use of intrinsically safe solutions is targeted. One way may be to shift to all-solid-state batteries with lithium metal anodes that enable a potentially high specific capacity of 3860 mAh / g and a redox potential of -3.04 V.

[0003] However, the cycle life of lithium metal anodes is plagued by, for example, the formation of porous and dendritic crystals as a result of battery charging in liquid electrolytes. In addition, lithium metal batteries are subject to one or more of several other problems, including cell short circuits due to hillock formation (non-uniform Li metal deposition), and over time, the formation of a porous and non-uniform anode structure that can lead to an increase in the diffusion paths of Li ions and electrons, and thus an increase in polarization, and the evolution of dead Li encapsulated by a film of solid electrolyte interphase (SEI) reaction products. These porous deposits also promote progressively larger volume changes within the anode during plating / stripping cycles, which can lead to poor life cycle stability.

[0004] US10741835 discloses an anode structure for a lithium metal battery, comprising a current collector, a seed layer selected to facilitate the electrochemical plating of metallic lithium deposited on the current collector, a separator, and a host structure between the seed layer and the separator for hosting metallic lithium during charging. A first adhesive layer and a second adhesive layer are required to bond the host structure to the seed layer and the separator, respectively.

[0005] S. Yoon (Journal of Power Sources, 2015, 279, 495) describes film anode carbon nanotubes (CNTs) for use in flexible lithium-ion batteries. The film anodes are based on disordered carbon nanotubes and are prepared by chemical vapor deposition and direct spinning. The carbon nanotubes support an anode metal. This study proposes heat treatment under a nitrogen atmosphere to affect performance.

[0006] JP2006 / 156351A relates to an anode for a lithium metal polymer secondary battery. The anode is made from an anode current collector metal foil or metal foam having a surface in which multiple recesses are indented into the metal current collector in a predetermined shape, either chemically by etching the surface or physically by pressing the surface of the metal current collector. The 3D metal structure contributes to the weight of the secondary battery.

[0007] DE102010008782A1 relates to a negative electrode comprising a conductive polymer matrix (metallized cloth or fleece) coated with a metal or metal alloy as a current collector, and a composite material at least partially embedded therein, wherein the negative electrode comprises at least one metal or metalloid, or an alloy thereof and / or an intermetallic phase, capable of forming an alloy or intermetallic phase with lithium.

[0008] EP3261157 describes a battery having a substrate current collector with metal pillars as a conductive structure covered with electrode and electrolyte layers. An insulator covers a portion of the conductive structure, preventing a conductive path between the first electrode and the second electrode. The metal pillars contribute to the battery's weight, and the insulator preventing the conductive path between the electrodes contributes to the battery's internal resistance. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 10741835 [Patent Document 2] Japanese Patent Publication No. 2006-156351 [Patent Document 3] German Patent Application Publication No. 102010008782 [Patent Document 4] European Patent Application Publication No. 003261157 [Non-patent literature]

[0010] [Non-Patent Document 1] Journal of Power Sources(Netherlands),2015 Vol.279,p.495-501 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] This disclosure mitigates one or more of the above-mentioned drawbacks by providing an anode, particularly an electrode comprising a 3D composite current collector, which has specific advantages for use with or as a host for a metal anode, while providing a combination of increased safety and cycle stability.

[0012] Generally, the concept of a 3D structured electrode comprises a conductive carrier having a 3D scaffold structure with multiple carbon-based protrusions coated to function as an anode of a metal electrode-based battery, for example, an upright pillar structure. The 3D scaffold structure can be of any geometric shape, preferably as upright pillars, or more preferably as a structure having holes or upright wall structures.

[0013] More specifically, in a preferred concept, the carbon-based protrusions of the 3D structured electrode are densely packed and then coated, and comprise a conductive 3D vertically aligned carbon nanotube scaffold that can function, for example, as an anode in a metal electrode-based battery.

[0014] In another preferred concept, a 3D structured electrode comprises spatially separated upright polymer protrusions, such as pillars or wall structures, which are coated and can function, for example, as an anode in a metal electrode-based battery.

[0015] Preferably, the electrode is suitable as an anode for a metal electrode-based battery.

[0016] The 3D composite current collector comprises a conductive substrate current collector having multiple laterally dispersed conductive upright scaffolding elements.

[0017] The scaffolding element comprises carbon-based protrusions extending in a direction away from the base on the substrate. In a preferred embodiment, the scaffolding element comprises a structure of aggregated carbon nanotubes oriented mostly parallel to the direction away from the substrate. Alternatively or additionally, the scaffolding element comprises polymer-based protrusions. The carbon-based protrusions may be conductive, which is typically the case with the structure of aggregated carbon nanotubes, or the carbon-based protrusions may be electrically resistive, which is often the case with polymer materials.

[0018] In the embodiment, for one or more of the scaffolding elements, the carbon-based protrusions comprise a structure of aggregated carbon nanotubes. Alternatively or additionally, for one or more of the scaffolding elements, the carbon-based protrusions are polymer-based protrusions.

[0019] Carbon-based protrusions, such as aggregated carbon nanotubes or polymer protrusion structures, are coated with a passivation layer. The passivation layer defines an outer wall that encapsulates the underlying composition, particularly the polymer or aggregated carbon nanotube structure. The passivation layer helps protect the underlying carbon-based protrusions from the base of the conductive substrate current collector, including along its sidewalls, up to the upper surface of the distal end of the structure away from the substrate, and including the upper surface.

[0020] As will be described in more detail herein, the electrodes disclosed herein can be advantageously used in many applications or configurations, including, but are not limited to, anodes comprising such electrodes, cathodes comprising such electrodes, and energy storage devices comprising the electrodes, for example, in one or more of the anodes and cathodes therein, or as one or more of them. Generally, these applications / configurations involve supplying one or more subsequent layers of functional material along the outer surface of a current collector forming a multilayer stack, e.g., a lithium metal battery multilayer. Thus, the upright scaffolding element can be understood as supporting one or more subsequent layers of functional material, e.g., a battery active layer, while providing the function of dispersed current collection / dispersion between the subsequent layers. Additionally, and as will be described in more detail below, the upright scaffolding element can be understood as reducing current density on a 3D surface, improving the uniformity of anode and / or cathode material dispersion, mitigating dendritic crystal formation, reducing irreversible loss of anode material during battery manufacturing and / or battery cycling, and / or reducing power density loss over battery life. [Means for solving the problem]

[0021] According to a first aspect, an electrode comprising a 3D composite current collector is provided, the 3D composite current collector comprising a conductive substrate current collector having a plurality of laterally dispersed conductive support elements, the support elements comprising a carbon-based protrusion extending in a direction away from the base of the substrate and a passivation layer covering the upright side wall including the tip of the carbon-based protrusion, whereby the passivation layer enables electron transport to the substrate and is composed of a first composition that is resistant to the transport of lithium (metallic metal and lithium ions) across the passivation layer, the passivation layer.

[0022] The passivation layer advantageously protects the protrusion underlying the support element from direct contact with the electrode material and / or electrolyte material, reducing or even essentially preventing its degradation due to a redox reaction resulting from a harmful chemical reaction between the battery active material, for example, lithium metal and the carbon-based composition contained in the protrusion. Additionally, by using a passivation layer that enables electron transport to the substrate, the conductivity of the substrate current collector can be maintained even when electrically non-conductive carbon-based protrusions (e.g., polymer protrusions) are used. The passivation layer can also advantageously provide a clearly defined and / or smooth surface regardless of the material of the underlying protrusion. Such a clearly defined and / or smooth surface is typically more suitable for the deposition of the electrode material than the outer surface of the carbon-based protrusion, which can be irregular, porous, and / or fluffy depending on the type of material.

[0023] The passivation layer is composed of a first composition 10c that enables electron transport to the substrate while being resistant to the transport of lithium across the passivation to the anode material and / or electrolyte material, for example, the protrusion structure. An elongated interstitial structure is defined in the complementary space between the opposing side walls of adjacent ones of the support elements.

[0024] In a preferred embodiment, the carbon-based protrusion tapers towards the tip, for example, a tapered pillar. The tapered shape can advantageously increase the overall surface area of ​​the 3D current collector while keeping the volume of battery inert material relatively low. In addition, as will become apparent from below, the inclined sidewall surface of the tapered protrusion, in contrast to vertical walls, improves control over the thickness of the subsequently added cover layer (e.g., by vapor deposition).

[0025] In a preferred embodiment, the carbon-based protrusions include an organic polymer.

[0026] In another preferred embodiment, the carbon-based protrusions consist of upright pillars formed from a carbon-based polymer or polymer composition material. A carbon-based polymer refers to a polymer whose polymer backbone contains carbon-carbon bonds, e.g., an organic polymer or polymer composition. Polymer protrusions may consist of thermoplastic resins, thermosetting resins, and / or elastomers. Suitable polymers may be selected from a list including, but not limited to, polyethylene, polypropylene, polyolefin, polystyrene, polycarbonate, polyethylene terephthalate, polyamide, polyacrylate, polyurethane, and liquid crystal polymers (LCP), and epoxy. In some embodiments, the protrusions, e.g., pillars, consist of essentially organic polymers.

[0027] Compared to metal or ceramic protrusions, carbon-based protrusions (such as those containing carbon nanotubes and / or polymer-based protrusions) can have a relatively reduced overall contribution to the total weight of the electrode, improving, for example, the power-to-weight performance of energy storage products.

[0028] Alternatively or in addition, the protrusions, such as pillar structures, may be composite materials comprising, for example, a polymer composition including one or more fillers and / or cover layers. The fillers and / or cover layers can advantageously increase the mechanical stability and / or thermal stability of the protrusions, for example, considering temperature or volume fluctuations during anode manufacturing and / or operating life in batteries. Preferably, the fillers are in the form of particles such as nanoparticles. Suitable examples of fillers are metal particles, carbon particles, ceramic particles, or combinations thereof. Conductive particles (e.g., carbon particles or metal particles) can be applied to increase the conductivity of the protrusions.

[0029] The filler may be present within the composite protrusion in an amount of 0 to 50% by weight relative to the weight of the protrusion, for example, 0 to 30% by weight or 1.0 to 25% by weight. Too much filler may adversely affect the structural properties and / or the weight of the protrusion.

[0030] Alternatively, or in addition to the presence of fillers and / or cover layers, the polymer composition protrusions may include pores. Advantageously, such pores can be applied to reduce the weight of carbon-based protrusions. Preferably, the pores represent 0 to 50 volume percent of the protrusion volume, for example, 0 to 30 volume percent or 1.0 to 25 volume percent. Excessive pore volume can adversely affect the structural integrity of the protrusion.

[0031] In some embodiments, the passivation layer includes a metal layer, which optionally extends along the surface of the substrate and thereby includes portions that interconnect adjacent conductive upright scaffolding elements. The metal layer can advantageously increase current collection between the substrate, particularly when the metal extends between adjacent protrusions.

[0032] Alternatively or in addition, the passivation layer may include a layer of semiconductor material. Semiconductor materials having conductivity between an insulator and a conductor (e.g., a metal) have the advantage of providing appropriate current collection while reducing the effective electric field toward the scaffold tip, thereby reducing the risk of dendritic crystal formation and / or improving battery cycle life, thanks to their resistivity, which can relatively reduce the plating potential of the anode metal (e.g., Li) near the tip of the scaffold element. Suitable semiconductor materials include titanium nitride, zirconium nitride, and indium tin oxide. To minimize overall reduced current collection performance, the layer of semiconductor material preferably extends between adjacent scaffold elements. Most preferably, the layer of semiconductor material is limited to upright protrusions.

[0033] In a preferred embodiment, the passivation layer is a laminate, which optionally includes a metal layer with a portion extending along the surface of the substrate, and a layer of semiconductor material, wherein the semiconductor material layer covers the metal layer and does not interconnect adjacent conductive upright scaffolding elements between adjacent protrusions.

[0034] In other or further preferred embodiments, the thickness of the semiconductor layer along the upright sidewall increases toward the tip. This gradually further reduces the effective electric field at the tip of the scaffold.

[0035] Preferably, the electrode may further include a sublayer extending between the carbon-based protrusions and the passivation layer. The sublayer can increase the mechanical and / or thermal stability of the carbon-based protrusions, particularly the organic polymer protrusions. The sublayer is preferably formed from an electrical insulator and interconnects adjacent conductive upright scaffolding elements. Suitable materials include, but are not limited to, silicon oxides and aluminum oxides, as well as ceramics and metal oxides.

[0036] A first composition included in or essentially forming the passivation layer may be formed from one or more metals selected from the group including, but not limited to, Cu, Ni, Al, and stainless steel, or a metallic composition that accepts a negligible amount of lithium, which can advantageously combine electronic conductivity with effective blocking of lithium diffusion.

[0037] In some embodiments, the first composition comprises, or essentially consists of, an electrical insulator having a thickness and resistivity configured to form a tunnel junction (e.g., Al2O3 or TiO2).

[0038] To improve the plating uniformity of the anode metal along the scaffolding surface, a seed layer can be provided to coat the scaffolding element. The seed layer may include a composition selected for alloying with lithium (e.g., Sn, In, Zn, Ag, Au, etc.).

[0039] In some embodiments, the electrode further includes an alkali metal anode layer (e.g., lithium) covering a plurality of scaffolding elements. The layer may be supplied before the initial charge cycle of the battery (e.g., from an external source). Alternatively, the layer may be formed as a result of the initial charge cycle or further charge cycles of the battery. To reduce the reactivity of the exposed surface of the anode metal, an anode passivation layer may be provided, preferably completely covering the anode metal layer. The anode passivation layer may consist of, for example, a metal or metalloid composition alloying with lithium metal. Alternatively or in addition, the anode passivation layer may consist of an organic or inorganic composition or a mixture thereof, as is known with SEI layers.

[0040] In further embodiments, the electrodes may be provided with an electrically insulating cap. The cap is provided to cover the top of the scaffolding element in order to reduce the electric field at the top. The electrically insulating cap may be provided on the anode passivation layer, between the anode metal layer and the anode passivation layer, or on the seed layer.

[0041] In other or further embodiments, the electrode further comprises an electrolyte coating the scaffold element. Alternatively or in addition, the electrode may further comprise particles of anode or cathode material.

[0042] The aspect ratio, defined by dividing the height of a protrusion by its width, can range from 1:1 to 10:1, or up to 20:1, for polymer-based pillars.

[0043] In preferred embodiments, the conductive substrate is provided as a flexible metal foil or as a metal-coated flexible carrier. The flexible substrate can be advantageously used to provide curved or flexible electrodes. Additionally, the flexible substrate can be processed effectively and consistently by a continuous manufacturing process such as roll-to-roll processing.

[0044] The electrode may also include an optional intermediate layer between the scaffolding element and the substrate current collector, the intermediate layer being chemically inert to the substrate current collector. In this way, degradation of the substrate current collector due to reaction with the scaffolding element, such as oxidation of the substrate current collector, can be reduced or even avoided. Alternatively or additionally, the adhesion of the scaffolding element to the substrate current collector can be improved. Suitable materials for the intermediate layer include metal oxides, titanium nitride, zirconium nitride, and ceramic materials such as indium tin oxide.

[0045] To enable the flexibility of the formed electrodes, laterally dispersed conductive upright scaffolding elements can be segmented into sectors, each sector having lateral separation from adjacent sectors by a gap according to the intended substrate bending axis.

[0046] In some embodiments, the electrodes disclosed herein can be provided on opposing surfaces of a single carrier substrate. Depending on the subsequent cover layer, for example, a type-specific battery active material provided on either surface, these dual electrodes can be used in series or bipolar assemblies of battery stacks.

[0047] Further embodiments of the present disclosure relate to energy storage devices comprising electrodes disclosed herein, such as lithium metal batteries. In some embodiments, the storage device may comprise a composite solid electrolyte membrane separating the opposing anode and cathode sides of the storage device.

[0048] Further embodiments relate to methods for manufacturing electrodes and / or batteries disclosed herein. Thus, a method for manufacturing electrodes disclosed herein is provided. The method includes providing a 3D composite substrate current collector having a conductive substrate current collector having a plurality of laterally dispersed carbon-based protrusions extending away from the base of the substrate, and coating the upright sidewalls including the tips of the carbon-based protrusions with a passivation layer (10) made of a first composition (10c) that enables electron transport to the substrate and is resistant to lithium transport over passivation. [Brief explanation of the drawing]

[0049] These and other features, aspects, and advantages of the apparatus, systems, and methods of this disclosure will be better understood from the following description, the appended claims, and the appended drawings.

[0050] [Figure 1A] A cross-sectional side view of the electrode disclosed herein is shown. [Figure 1B] A partial cross-sectional side view of an embodiment of the electrode disclosed herein is shown. [Figure 1C] This specification provides a partial cross-sectional view of an embodiment of the electrode disclosed herein. [Figure 1D] This specification provides a partial cross-sectional view of an embodiment of the electrode disclosed herein. [Figure 1E] This specification provides a partial cross-sectional view of an embodiment of the electrode disclosed herein. [Figure 1F] This specification provides a partial cross-sectional view of an embodiment of the electrode disclosed herein. [Figure 1G]This specification provides a partial cross-sectional view of an embodiment of the electrode disclosed herein. [Figure 2A] A partial cross-sectional side view of an embodiment of a 3D anode comprising the electrodes disclosed herein is shown. [Figure 2B] A partial cross-sectional side view of an embodiment of a 3D anode comprising the electrodes disclosed herein is shown. [Figure 3A] A top cross-sectional view of the electrode disclosed herein is shown. [Figure 3B] Various embodiments of a 3D anode, including an electrical insulating cap, are depicted. [Figure 4A] Various embodiments of a 3D anode, including an electrical insulating cap, are depicted. [Figure 4B] Various embodiments of a 3D anode, including an electrical insulating cap, are depicted. [Figure 5A] Further embodiments of the electrodes disclosed herein are illustrated below. [Figure 5B] A cross-sectional side view of the electrode disclosed herein is shown. [Figure 6A] A schematic side view of a battery equipped with the electrodes disclosed herein is provided below. [Figure 6B] Further embodiments of the electrodes disclosed herein are illustrated below. [Figure 6C] Further embodiments of the electrodes disclosed herein are illustrated below. [Figure 7A] A schematic example of a method for manufacturing the electrodes disclosed herein is provided below. [Figure 7B] This specification provides a schematic top view of an embodiment relating to the manufacture of an electrode disclosed herein. [Modes for carrying out the invention]

[0051] The terms used to describe specific embodiments are not intended to be limitations of the invention. Where used herein, the singular forms "a," "an," and "the" are intended to also include the plural forms unless the context otherwise explicitly indicates. The terms "and / or" include any and all combinations of one or more of the associated listed items. The terms "comprises" and / or "comprising" will be understood to specify the presence of a described feature, but not to exclude the presence or addition of one or more other features. Where a particular step of a method is referred to as following another step, unless otherwise specified, it should be further understood that it may follow that other step directly, or one or more intermediate steps may be performed before the particular step. Similarly, where connections between structures or components are described, it should be understood that these connections may be established directly or through intermediate structures or components, unless otherwise specified.

[0052] As used herein, the terms anode and anode composition may be understood to refer to elements and materials that function as negative electrodes, respectively, during the normal discharge routine of a battery, releasing electrons in an electrochemical oxidation reaction with the anode / anode material, which acts as acceptor / reducing material. Cathode and cathode composition relate to their corresponding counterparts (positive electrode / electron acceptor). During the charging routine, the roles of oxidizer / reducing agent are obviously reversed.

[0053] The present invention is described in full below with reference to the accompanying drawings illustrating embodiments of the invention. In the drawings, absolute and relative sizes of systems, components, layers, and areas may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-sectional illustrative drawings of idealized embodiments and intermediate structures of the invention. In the description and drawings, similar figures refer to similar elements throughout. Relative terms, and their derivatives, should be interpreted as referring to orientations as described thereafter or shown in the drawings considered. These relative terms are for illustrative purposes only and do not require the system to be constructed or operated in a particular orientation unless otherwise specified.

[0054] In relation to embodiments comprising aggregated carbon nanotube structures, where specific features are described / depicted, it will be understood that, unless otherwise stated or evident from the context, such features are equally assumed to be in relation to other carbon-based structures (e.g., polymer-based pillars).

[0055] Conversely, features described / depicted in relation to embodiments having polymer-based protrusions will be understood to be equally assumed in relation to embodiments having carbon nanotube-based protrusions, unless otherwise stated or evident from the context.

[0056] Figure 1A illustrates a cross-sectional side view of an electrode 1 as disclosed herein. The electrode is illustrated to include a 3D composite current collector 2. The current collector comprises a conductive substrate current collector 3 having a plurality of laterally dispersed conductive upright scaffolding elements 4. The scaffolding elements 4 comprise carbon-based projections 6, in this case, structures of aggregated carbon nanotubes 7 oriented mostly parallel to the direction away from the substrate 3. The carbon-based projections 6 are covered with a passivation layer 10 to shield the carbon nanotubes 7 from direct contact with the electrode material (e.g., an anode metal) and / or electrolyte, thereby comprising a first composition 10c that enables electron transport between the aggregated carbon nanotube structures. The passivation layer 10 defines an outer wall including the side walls 5 of the upright scaffolding elements. Elongated interspace structures 5i between adjacent scaffolding elements 4 provide space for a continuous functional layer.

[0057] Advantageously, the conductive substrate can be provided as a flexible metal foil, e.g., copper foil, or as a metal-coated flexible carrier 3C, e.g., a metal-coated plastic film, as illustrated in Figures 1B, 5A, 6A, and 6B. The flexible metal foil and / or metal-coated carrier advantageously allow for reduced manufacturing time by enabling the electrodes to be coiled, conform to the shape of the external 3D-shaped carrier, and / or facilitating a roll-to-roll manufacturing process.

[0058] It will be understood that the shape and dimensions of the scaffolding element 4 may depend on the application. Typically, the height s7 of the carbon-based protrusion 6 is at least 2 μm. The taller the structure, the more pronounced the 3D current collection effect becomes, for example, the larger the amount and volume of electrode material that can electrically communicate with the current collector. Upper limits may simply be defined by process limitations. For example, specific upper limits, such as limitations on providing carbon nanotube structures exceeding >100 micrometers (μm), and / or limitations on providing a conformal coating layer at the base of the structure. Structures with heights in the range of 5 μm to 50 μm have been found to strike a practical balance between device performance, such as overall capacity, and manufacturing complexity.

[0059] A buffer layer is typically provided between the conductive substrate current collector and the carbon nanotubes, on which the carbon nanotubes grow. As is known in the art, the buffer layer typically includes an oxide layer, which may be a conductive oxide that provides catalyst seed particles that catalyze the growth of the carbon nanotubes. Depending on the growth conditions, catalyst residue may remain at the bottom interface of the carbon nanotubes (base-type carbon nanotube growth), and / or catalyst residue may be present at the end tips of the carbon nanotubes (tip-type growth).

[0060] The lateral separation w1 between the opposing side walls 5 of adjacent carbon-based protrusions 6, e.g., aggregated structures of carbon nanotubes 7, determines the dimensions of the interspatial structure 5i and therefore the volume available for the deposition of subsequent layers of electroactive material (e.g., electrode or electrolyte material). The closer adjacent scaffolding elements are positioned, the more uniform the current collection from the subsequent cover layer can be. Furthermore, the greater the separation of adjacent scaffolding elements and the smaller their lateral dimensions, the greater the volume available for subsequent layers of functional electroactive material and the smaller the relative contribution of carbon nanotubes.

[0061] The practical range for lateral dimensionalization of the structure, for example, the cross-sectional separation w2 between opposing side walls 5 of the carbon-based protrusions 6, was found to be in the range of 0.1 μm to 20 μm. The thinner the structure, the smaller the contribution of the carbon nanotube structure to the overall weight and volume compared to the electroactive material disposed along the structure and between it. A value of approximately 100 nm was found to constitute a practical lower limit for a practical balance between increasing reduction and manufacturing complexity.

[0062] The shape of the scaffolding element can include one or more of the following: isolated structures such as pillars or cylinders; wall structures with elongated dimensions in the lateral direction along the substrate; patterned, e.g., zigzag wall structures; and interconnected wall structures with wall cross-sections. Pillar-shaped structures can provide the maximum surface area per unit volume of carbon, while scaffolding elements have a smaller surface / volume ratio. Such structures have dimensions that extend laterally along the substrate, such as wall cross-sections, patterned wall cross-sections (e.g., zigzag), or interconnected wall cross-sections, which can advantageously provide increased resilience to forces along the lateral direction (e.g., bending). Figure 7B (right) provides a top view of an exemplary structure of aggregated carbon nanotubes arranged in a hexagonal pattern.

[0063] The passivation layer 10 comprises, or essentially consists of, a first composition 10c that enables electron transport between the aggregated carbon nanotube structure and the first composition 10c. The passivation layer of the first composition 10c extends along the outer surface of the aggregated carbon nanotube structure from the base of the conductive substrate current collector to the terminal end and tip of the structure. Obviously, the passivation layer can also extend along the conductive substrate current collector 3 between adjacent carbon-based protrusions 6 (e.g., between adjacent aggregated carbon nanotube structures or between adjacent polymer-based protrusions).

[0064] Advantageously, the passivation layer 10 can form an essentially closed coating, or shell, while enabling electron transport capability between it and the aggregated carbon nanotube structure. Providing an essentially closed shell reduces the possibility of foreign substances, such as electroactive materials, coming into contact with individual carbon nanotubes 7 and entering the internal volume 7i within the structure, i.e., between adjacent carbon nanotubes 7.

[0065] Thus, the application of the shielding coating, i.e., the passivation layer 10, has been found to mitigate or even prevent degradation of the carbon nanotube structure due to interactions between carbon nanotubes, such as irreversible chemical reactions, resulting from direct contact with electroactive materials, particularly highly reactive anode metal compositions, especially at defect sites. Additionally, the passivation layer 10 has been found to minimize the loss of functional electroactive materials, such as anode metals, due to interactions with carbon nanotubes. Furthermore, the passivation layer 10 has been found to increase the cycle life of electrochemically active devices comprising the electrode 1 by increasing the structural integrity of the scaffold 4 and reducing volume changes within the carbon-based protrusions 6, such as porous polymer-based protrusions or pores in the interior 7i of the aggregated carbon nanotube structure, thereby preventing or essentially avoiding the infiltration of electrode metals / metal ions into the void spaces of the carbon-based protrusions 6.

[0066] Advantageously, the passivation layer 10 may be provided such that the penetration of the passivation material into the structure of aggregated carbon nanotubes passing through the outermost portion surrounding the inner core can be minimized, resulting in the coating material forming a shell, thereby allowing the voids defined as the spaces between adjacent aggregated carbon nanotubes in the central portion of the structure to remain essentially free of the coating material, i.e., the first composition 10c. Clearly, the shielding material can permeate to some extent between the carbon nanotubes in the outermost portion of the structure of aggregated carbon nanotubes forming the composite zone. However, as will be described in more detail below, the thickness of this composite zone can be well less than 25 nm, e.g., less than 5 nm, leaving a core in which the aggregated carbon nanotubes can remain in an uncoated state. Limiting the passivation composition to the outermost portion of the structure advantageously minimizes the total weight per unit volume of the electrode while maintaining current collection / dispersion characteristics.

[0067] Generally, the passivation layer 10 comprises, or essentially consists of, a composition referred to as the first composition 10c, which has reduced reactivity to carbon nanotubes, particularly to defect sites, compared to the anode or cathode composition, and the corresponding electrolyte composition in contact with the electrode. Preferably, composition 10c is selected to have significantly reduced, preferably negligible, electrochemical activity under normal operating potentials.

[0068] The inventors found that the objective of providing a closed passivation layer 10 for shielding carbon nanotubes 7 to prevent direct contact with external materials while enabling electron transport between them and carbon-based protrusions 6 can be achieved by a conductive composition.

[0069] Therefore, in some embodiments, the first composition 10c (contained in or essentially constituting the passivation layer) includes or essentially consists of a metal, a metalloid, or a mixture of one or more metals and / or metalloids, such as an alloy.

[0070] The metal and / or metalloid-based composition for the passivation layer 10 is generally selected from elements having electronegativity >1.5 on the Pauling scale. A preferred composition 10c may contain, or essentially consist of, elements selected from the later d-block and early p-block of the periodic table, i.e., groups 9 to 14 of the periodic table. To shield the carbon nanotubes 7 from direct contact with electrode or electrolyte materials (electroactive materials), such as an anode metal composition, for example, a metal selected from alkali and / or alkaline earth metals, including but not limited to Li, Na, K, and Mg, the metal and / or metalloid-based composition for the passivation layer is preferably formed from a fairly noble composition containing, or preferably essentially consisting of, elements selected from the group consisting of nickel, copper, titanium, aluminum, and combinations thereof, of which copper, nickel, and their alloys are most preferred from a practical and / or economic standpoint. Naturally, semiconductor materials, including, but not limited to, TiN, ZrN, or ITO, may be used as alternatives or additions.

[0071] Aluminum was found to be particularly stable for shielding the carbon nanotubes 7 from direct contact with the cathode composition and / or electrolyte, while copper was found to be less preferable, particularly due to its relatively low electrochemical stability at high operating potentials (>3V), although similar compositions could be used in principle. The thickness of the metal or metalloid-based passivation layer 10 is at least such that it provides a functionally closed conformal cover layer. Suitable deposition techniques include dry deposition methods such as PVD (physical deposition), ALD (atomic layer deposition), and spatial ALD, optionally followed by wet deposition techniques such as electrochemical deposition or plating to increase the thickness of the passivation layer 10. In absolute terms, the metal or metalloid-based passivation layer can already be formed with a thickness of about 2 nm. To reduce the density of point defects, the thickness is preferably >5 nm. Thicker layers, e.g., >10 nm, >25 nm, or even >100 nm, are also effective. However, in order to minimize the contribution of the passivation layer to the overall weight of the electrode, the thickness of the metal or metalloid-based passivation layer is preferably <200 nm, for example, in the range of 5-10, 5-20 nm, 5-50 nm, 10-50 nm, or 10-100 nm.

[0072] The inventors have surprisingly found that the objective of providing an effective passivation layer 10 for shielding carbon nanotubes from direct contact with external materials while enabling electron transport between the aggregated carbon nanotube structure and the carbon nanotube structure can be equally achieved by a composition generally considered to be electrically insulating, provided that such a layer is functionally thin and allows electron tunneling across the coat while shielding the underlying carbon-based protrusions from direct contact with external materials. Thus, in some embodiments, the first composition 10c comprises or essentially consists of an electrically insulating composition such as a metal and / or mixed metal oxide. For effective tunneling across the passivation layer, the surface of the carbon-based protrusion to which the passivation layer 10 is applied should be in electrical contact with the substrate current collector 3. This is the case, for example, for conductive carbon-based protrusions such as carbon nanotubes, or polymer-based protrusions comprising a polymer material having a conductive filler.

[0073] Suitable materials that can be used in the first composition 10c to form the tunnel junction include metal oxides such as HfOx, ZrOx, LaOx, SiOx, AlOx, and TiOx, mixed metal oxide compositions such as SrTiOx(STO) and BaSrTiOx(BST), and mixtures of metal oxides and / or mixed metal oxides. Particularly preferred materials include silicon oxide, aluminum oxide, titanium oxide, and combinations thereof, and these conformal layers can be effectively provided by atomic layer deposition. The maximum thickness of the layer that can produce sufficient tunneling depends on the material used, but is typically 5 nm or less. Therefore, the thickness of the insulator-based passivation layer is generally <5 nm, preferably 3 nm or less. The minimum thickness is generally >1 nm. Advantageously, the conformal insulator-based passivation layer 10 can be as thin as five single layers. Advantageously, metal oxide-based passivation layers were found to be particularly effective in shielding carbon nanotubes from electrode and electrolyte compositions under both anode and cathode conditions.

[0074] In preferred embodiments, particularly when electrode 1 is used as part of or as an anode, electrode 1 further comprises a seed layer 20 covering a scaffold element 4 for receiving the anode metal composition, as shown in Figure 1B. Advantageously, the seed layer can be deposited directly onto the scaffold element, i.e., without an intermediate adhesive layer, minimizing the amount of dead material per unit volume. To further minimize its contribution to the overall weight of the electrode, the seed layer 20 is preferably functionally thin, typically in the range of about 2 nm to about 100 or 200 nm, preferably 5 to 50 nm, with increasing thickness of the seed layer reducing the density of point defects at the expense of an increase in relative weight contribution. The seed layer 20 is generally formed from a composition 20c having a high affinity for one or more anode metal compositions selected from alkali and alkaline earth metals. Thus, the seed layer 20 can be understood as providing an effective wetting layer that improves the uniformity of the anode metal layer deposited or plated thereon. This reduces or essentially avoids localized or non-uniform anode metal deposition, thereby mitigating the occurrence of lithium dendritic crystal and / or porous (mossy) anode metal layer growth, even during long battery cycles. Providing such a seed layer 20 contributes to the objectives of increasing battery safety (by reducing dendritic crystal formation), improving cycling life, and increasing power density (by reducing porous / mossy anode metal formation). Suitable compositions include materials generally considered to be lithophilic, sodium-philic, potassium-philic, etc. In some embodiments, the seed layer 20 comprises or essentially consists of a seed composition 20c alloyed with the anode metal composition, for example, having affinity for the anode metal and enabling the formation of a mixture having a seed element content of >10 wt%, e.g., >50%, or 0-100 wt%. Particularly preferred seed compositions 20c include zinc and zinc oxide, or tin and tin oxide, which are found to be reduced to their corresponding metallic states upon initial contact with a more electropositive anode metal, such as Li or Na, or preferably by a prior reduction step involving hydrogen.Both Zn and Sn, as well as their oxide-based seed layers, can be advantageously provided as essentially closed conformal cover layers, for example, by ALD. Naturally, if the electrode is used on the cathode side for energy storage applications, or is intended to be used as a cathode-side electrode, a seed layer for the anode metal is not required.

[0075] In preferred embodiments, the electrode is intended for use as an anode or as part of an anode, and further comprises a layer of anode composition, typically an anode metal composition, or a cathode composition covering a plurality of scaffold elements. Using an anode composition, the electrode is also referred herein to as a pre-filled anode or a pre-filled 3D anode. Using a cathode composition, the electrode is also referred herein to as a pre-filled cathode or a pre-filled 3D cathode.

[0076] Figures 1C to 1G illustrate the electrode features described herein for embodiments in which the scaffold structure is embodied by a carbon-based pillar 6p. The embodiment illustrated in Figure 1C differs from the embodiment described in relation to Figure 1A primarily in that the pillar is formed from a polymer, provided on a carbon base. For example, the polymer-based pillar 6p is a passivation layer covering the pillar, extending from the base of the substrate 3 along its sidewalls to the tip of the polymer pillar, and including the tip. Polymer protrusions such as the polymer pillar structure may be provided by methods known in the art, including but not limited to photolithography patterning, (micro)imprinting, and (screen)printing. In contrast to carbon nanotube-based scaffold elements, polymer-based scaffold elements can have a smaller range of aspect ratios (height / width), for example, preferably at least 1:1 to 10:10, or 20:1.

[0077] The embodiment shown in Figure 1D differs from the embodiment described in relation to Figure 1C, primarily in that the pillar has a tapered shape in the direction from the base 6b of the pillar to the tip 6t of the pillar. The tapered projection is accessible using the general methods listed above, for example, by using a mold of the appropriate shape. The side walls can be inclined in a continuous linear manner, as shown, but are not necessarily required.

[0078] In the embodiment shown in Figure 1D, the passivation layer further includes portions 10p connecting adjacent scaffolding elements 4. Portions 10p cover the surface of the substrate 3 between adjacent carbon-based, or for example, polymer-based, pillars 6p. To maintain high conductivity with the substrate 3, the interconnection section (portion 10p) is preferably metallic.

[0079] An optional intermediate layer (not shown) may be provided between the scaffolding element 4 and the substrate. Preferably, the intermediate layer is made of a material that is chemically inert to the substrate current collector. In this way, degradation of the substrate current collector due to reaction with the scaffolding element, such as oxidation of the substrate current collector, can be reduced or even avoided. Oxidation of the substrate current collector is undesirable because it can adversely affect the structural integrity and / or conductivity of the current collector. Alternatively or additionally, the adhesion of the scaffolding element to the substrate current collector can be improved. In one embodiment, the intermediate layer is provided only between the scaffolding element 4 and the substrate 3. In another embodiment, the intermediate layer may also be provided on a portion of the substrate between adjacent scaffolding elements 4, for example, the entire substrate. In that case, the intermediate layer is preferably made of an electronically conductive material compatible with additional layers that may (directly) contact the intermediate layer, such as an alkali metal anode layer and an electrolyte layer. Suitable materials for the intermediate layer include ceramic materials such as metal oxides. If the intermediate layer needs to be conductive, conductive oxides such as indium tin oxide are preferred.

[0080] In the embodiments shown in Figures 1E and 1F, the passivation layer is a laminate. The laminate includes a metal base layer 10a and a cover layer 10b. The base layer 10a extends between adjacent pillars, but does not need to. The cover layer 10b is made of a material having a lower electronic conductivity than the base layer, such as a semiconductor. In contrast to the base layer, the cover layer 10b does not extend between adjacent protrusions. Preferably, the cover layer 10b is limited to the protrusions, for example, as shown. In a preferred embodiment, for example, as shown in Figure 1F, the cover layer 10b has a thickness that increases from a minimum at or near the base 6b of the protrusion (e.g., pillar or wall) to a maximum at or near the top 6t of the protrusion.

[0081] Figure 2A depicts a partial cross-sectional side view of an embodiment of electrode 1 including a layer of anode metal 30. The anode metal layer includes or essentially consists of an anode metal composition 30c. As shown, the layer is provided directly on top of the seed layer 20 and forms a homogeneous cover layer on the scaffolding elements. The anode metal layer 30 also extends between adjacent scaffolding elements in a direction along the adjacent scaffolding elements. By providing the anode metal composition 30c, the electrode can be advantageously configured as a pre-filled anode for energy storage applications (e.g., batteries).

[0082] In some embodiments, for example, as shown in Figure 2A (left), the layer of anode metal composition 30c is configured to leave space in the inter-spatial structure 5i between adjacent scaffolding elements for a subsequent battery layer containing one or more electrolytes and / or anode materials, forming a 3D battery structure that can benefit from increased power density compared to a 2D layer battery structure, due to a relatively short ion diffusion distance, which facilitates the deposition of functional battery multilayers along the upright sidewalls of the scaffolding elements 4.

[0083] In some preferred embodiments, the anode metal essentially fills the inter-spatial structure between adjacent upright scaffolding elements, and for example, as shown in Figure 2A (right), scaffolding element 4 is essentially embedded in the anode metal composition 30c. Embodiments in which scaffolding element 4 is essentially embedded in the anode metal composition 30c are understood to constitute a planar 2D anode with an internal 3D current collector element that provides distributed current collection and improved electric field uniformity, while benefiting from a passivation layer that provides chemical and mechanical stability that can be used for battery storage applications. Compared to 3D layered battery structures, battery structures including a planar 2D anode can offer a relatively advantageous capacity per unit volume.

[0084] Clearly, the anode metal composition can be provided directly on the carbon-based protrusions 6, i.e., without the passivation layer 10. However, such a configuration would not benefit from the advantages, including improved structural and electrochemical stability, that are provided by the passivation layer as disclosed herein.

[0085] Suitable anode materials include compositions comprising metallic elements selected from the alkali and / or alkaline earth group. Preferably, one or more of lithium, sodium, potassium, and magnesium, of which lithium is particularly preferred for energy storage applications that benefit from the maximized oxidation potential provided by Li. In some embodiments, the anode metal composition is an alloy comprising one or more elements selected from the alkali and / or alkaline earth group alloyed with one or more transition metal elements or metalloid elements such as zinc. Alloying reduces the overall reactivity of the composition to oxidation, particularly oxidation during electrode / battery manufacturing or assembly due to contact with the environment, at the cost of a theoretical penalty in the achievable overall energy density and / or oxidation potential. The inventors have found that losses resulting from alloying an alkali or alkaline earth-based anode metal composition with a relatively unreactive (low electronegativity) metal composition, such as Li-Zn(90 / 10 w / w) to Li-Zn(80 / 20), may outweigh performance losses resulting from oxidation of the anode metal composition, which is essentially an alkali or alkaline earth-based anode metal composition, particularly those imparted during manufacturing under conventional typical dry chamber manufacturing conditions (an atmosphere containing O2, N2, and CO2 but essentially free of water vapor). Therefore, in a preferred embodiment, the anode metal composition comprises an alloy between one or more metals selected from alkali or alkaline earth-based anode metal compositions, preferably lithium, and 5 to 30 weight percent of the composition to be alloyed with it, wherein the composition comprises or essentially consists of elements selected from groups 12 to 14, preferably one or more of Zn, Sn, In, Al, and Si, more preferably at least Zn.

[0086] It will be understood that the anode metal layer can be suitably provided by known deposition methods, including, but not limited to, dry deposition methods such as PVD and ALD, molten deposition, and wet deposition processes such as electroplating, for example, as a conformal cover layer or to essentially fill the interstellar structure.

[0087] Alternatively, electrodes can be manufactured without an anode metal layer. Such electrodes can be used on the anode side of energy storage applications (e.g., Li-metal batteries), where the anode metal is provided by an in-situ plating procedure (conditioning step) in which the anode metal is plated onto a scaffold by reducing metal ions from the electrolyte composition. Compared to pre-filled embodiments, electrodes without an anode metal layer can benefit from a relatively increased storage life.

[0088] Alternatively, the anode or cathode composition can be provided as fine particles, for example, by depositing it as a slurry using a volatile carrier. Thus, in some embodiments, the electrode comprises particles of the anode material, which at least partially fill the interspatial structures between the upright scaffolding elements. Thus, in some embodiments, the electrode comprises particles of the cathode material, which at least partially fill the interspatial structures between the upright scaffolding elements. In embodiments comprising a cover having particles of the anode material, it will be understood that the scaffolding elements may further advantageously include one or more of the functional conformal layers described herein, such as a seed layer (e.g., during battery charging routines) for improving the homogeneity of the anode metal (e.g., lithium) plating, and / or an electrical insulating cap 50 for reducing the electric field near the tip of the scaffolding structure.

[0089] In particular for electrodes containing particles of anode material (each a cathode material), to improve electrical and / or ionic contact between the anode material and each cathode material, the electrode is preferably further provided with a corresponding cathode liquid or anode liquid composition. The cathode liquid / anode liquid can advantageously bridge ionic / electronic state pathways between the electrode and the separator structure and / or solid or semi-solid electrolyte superimposed thereon. In the case of electrodes containing particulate anode / cathode material compositions, the anode liquid / cathode liquid can advantageously fill the remaining gap volume between particles, further improving electron / ionic conduction between adjacent particles.

[0090] In some preferred embodiments, if the electrode comprises a layer of anode metal composition, the electrode may further advantageously comprise an anode passivation layer.

[0091] Figure 2B depicts a partial cross-sectional side view of an embodiment of electrode 1 shown in Figure 2A (left), further comprising an anode passivation layer 40. The anode passivation layer 40 is composed of, or essentially consists of, a passivation composition 40c. The anode passivation layer 40 forms a conformal cover layer that shields the underlying anode metal composition 30c from direct contact with the surroundings. Clearly, the anode passivation layer 40 can offer similar advantages to embodiments in which the scaffolding element 4 is essentially embedded within the anode metal composition 30c (as shown, for example, in Figure 2A, right).

[0092] To protect the underlying anode while minimizing electrochemical activity, the passivation layer is formed from a composition comprising, or essentially comprising, an anode metal- or at least anode metal ion-conductive or miscible composition having relatively reduced reactivity to one or more, preferably all, of O2, N2, CO2, and H2O. The anode metal conductive or anode metal ion conductive or miscible composition can be understood as a composition having a non-zero, typically at least 5%, preferably more, e.g., >10% or >25%, by weight of the alkali and / or alkaline earth metal-based anode metal composition and / or corresponding ions contained in the anode layer. Suitable compositions include those comprising, or essentially comprising, elements selected from one or more of Group 12 to 14, preferably Zn, Sn, In, Al, and Si, all of which have been found to alloy with desired anode metal compositions such as Li, Na, and Li / Na, each having relatively reduced reactivity to at least one of O2, N2, CO2, and H2O. Metals or metalloids can be suitably deposited using known processes, for example, by PVD. Most preferably, the passivation composition contains at least Zn or Tin, which has been found to be particularly effective in shielding the underlying anode metal, such as Li, from decomposition by O2, N2, H2O, and CO2, while being suitable for layer deposition by dry deposition techniques including PVD and ALD. The passivation layer is preferably thin to reduce the reaction of the underlying anode metal composition with surrounding components. Preferably, the layer has a thickness of at least 5 nm. To reduce the point defect density, the layer may be thicker, for example, ≥10 nm. To minimize the overall weight contribution of the anode passivation layer, the thickness is preferably about 250 nm, for example, 5–200 nm, 10–100 nm, or 20–50 nm. In some embodiments, the passivation layer consists of one or more layers of Sn, Zn, or Al having a thickness in the range of 5–250 nm.The inventors found that each of Sn, Zn, or Al provides sufficient solubility for anode metals such as lithium and sodium, while simultaneously mitigating their oxidation during electrode fabrication and / or battery assembly under dry chamber conditions, with a negligible effect on power density.

[0093] Considering the mutual solubility of the compositions constituting the anode metal layer 30 and the anode passivation layer 40, it will be understood that it may be difficult to identify a clear transition / boundary between the anode passivation layer and the anode metal layer, especially in increasing battery cycle routines (charge / discharge routines).

[0094] Alternatively or in addition, the anode passivation layer may include a stable solid electrolyte interface (SEI) composition. SEI compositions are known in the art and can be formed as a result of an irreversible reaction between anode metal components and the corresponding electrolyte composition. In this disclosure, it is particularly assumed that a stable SEI coating is provided by reacting with a dedicated electrolyte composition using a dedicated wet electrochemical deposition process. Engineering Reports 2021;3:e12339 by Gu et al., which is incorporated herein by reference in its entirety, discusses several reports on the formation of stable SEI layers (Section 3.3) and lithium alloys (Section 3.1), which are also incorporated herein by reference.

[0095] The embodiments described in relation to Figures 2A and 2B should not be interpreted as being limited to carbon nanotube 7-based pillars, and it should be noted that this description also applies to other carbon-based protrusions, particularly polymer-based protrusions such as pillars and wall structures, as described in relation to Figures 1C-1G and 7B.

[0096] Figure 3A provides a depiction of a cross-sectional top view of an electrode, as shown in Figure 2B, showing a scaffold element 4 comprising a stack of conformal cover layers including a seed layer 20, an anode metal layer 30, and an anode passivation layer 40. In this particular embodiment, carbon-based protrusions 6, illustrated as structures of aggregated carbon nanotubes, are formed as separation pillars having a circular cross-section. While separation structures, particularly separation pillars, may be preferred in general to provide the greatest surface-to-volume ratio, it will be understood that this disclosure should not be construed as being limited to such structures. The inventors also explicitly envision separation structures of different shapes, such as having square or different polygonal cross-sections, but also envision structures having elongated cross-sectional dimensions in the direction along the conductive substrate current collector, such as walls, or even interconnected structures such as interconnected wall cross-sections, such as the hexagonal interconnected wall cross-section shown in Figure 7B. Interconnected structures may offer particular advantages in terms of relatively improved mechanical stability, such as resistance to bending and / or delamination on structures having separation protrusions. A wall structure, particularly a wall section of an interconnected structure, may be further provided with one or more channels that at least partially interrupt the wall section. Such channels may be applied to electrodes when manufacturing batteries, improving access to the space between adjacent wall sections for subsequent layers, such as an electrolyte layer.

[0097] In particular, for aggregated carbon nanotube structures or thin polymer-based structures, the lateral dimension of the separated or interconnected structures is preferably not greater than 10 mm, and typically less than 1 mm, in order to reduce cracking or structural damage. Limiting the lateral dimension of the interconnected structures allows for bending of the underlying substrate, and indeed the electrodes as a whole, without loss of essential function.

[0098] In a preferred embodiment, carbon-based protrusions 6, such as aggregated carbon nanotube structures or polymer-based protrusions (having elongated dimensions laterally along the substrate, e.g., pillar / wall structures), are segmented into sectors, each sector separated by adjacent sectors across a gap. Thus, in a preferred embodiment, carbon-based protrusions 6 are segmented into sectors having lateral separation along the substrate bending axis. The gap typically has dimensions in a range with a lower limit of about 5 μm. Preferably, the gap is finally equal to the height of the protrusion, e.g., the height of the polymer-based pillar or carbon nanotube, e.g., 5 to 100 μm. Further separation can allow for smaller bending radii. The upper limit can be several millimeters or more. Typically, the separation is in the range of 5 to 2000 μm, preferably 50 to 1000 μm, and more preferably 100 to 500 μm.

[0099] Alternatively or in addition, as shown in Figure 5A, for example, upright scaffolding elements 4 can be provided on opposing surfaces of the conductive substrate current collector. Figure 5A illustrates an embodiment comprising a conductive substrate current collector 3 having a flexible polymer carrier film 3c coated with copper films 3-1, 3-2 on opposing surfaces. On both sides of the conductive substrate current collector 3 are provided upright scaffolding elements 4-1, 4-2, respectively, as disclosed herein.

[0100] The scaffolding elements on opposing sides of the substrate can be coated with the same electrode material (e.g., identical or similar anode or cathode compositions on both sides). Alternatively, the scaffolding elements can be provided with anode material on one side and cathode material on the other side (e.g., in bipolar stacking). In bipolar stacking, layers 3-1 and 3-2 typically do not contain the same metal (Cu). Instead, it may be preferable that one side is coated with Cu and the other side with a different metal, preferably Al. It is well understood that the choice may depend on the voltage of the electrode material.

[0101] In some preferred embodiments, the electrodes further comprise an electrical insulating cap. Figures 3B, 4A, and 4B illustrate various embodiments of a 3D anode including an electrical insulating cap. The cap 50 covers the top section s5 of the scaffolding element. The cap 50 may be provided, for example, between the seed layer 20 and the anode metal layer 30, between the anode metal layer 30 and the anode passivation layer 40, and / or covering the anode passivation layer 40. By covering the top section of the scaffolding element, the electric field near the top section of the upright scaffolding element can be effectively reduced. Reducing the electric field near the top section of the scaffolding element 4 can favorably reduce the deposition of non-uniform anode metal, such as lithium, during the battery cycle. Reducing non-uniform anode metal deposition near the top of the scaffolding structure can reduce or eliminate the formation of dendritic crystals that could cause short-circuit conditions. Reducing the non-uniform anode metal deposition near the top of the scaffolding structure is further found to improve the uniformity of anode metal deposition along the uncoated sidewall cross section of the structure, which improves cycling life and / or power density during battery operation.

[0102] The cap is preferably formed of a metal or mixed metal oxide or other dielectric inorganic composition 50c. The higher the dielectric constant, the thinner the capping layer can be relative to a given insulating effect. Preferably, the insulating composition 50c has a dielectric constant of at least about 1, more preferably k>10, or k>100. Suitable compositions include SiOx, AlOx, TiOx, HfOx, ZrOx, LaOx, and mixed metal oxide compositions, e.g., STO(SrTiOx), BST(BaSrTiOx), and mixtures thereof. A non-limiting description of exemplary dielectric compositions can be found in Jain et al., IEEE Trans. Advanced Packaging 25(3)454 (2002), which is incorporated herein by reference. It will be understood that the insulating cap is deposited, for example, by dry deposition, such that the bottom portion of the scaffolding remains essentially uncovered by the cap. Generally, the cap is limited to the top portion of the scaffolding element. Typically, the cap extends over a distance of <25% of the length of the carbon nanotube, and over the length of the sidewall of the scaffolding element.

[0103] In one embodiment, the cap is provided directly on the passivation layer. Alternatively, or in addition, the cap may be provided directly on a seed layer (Figure 4B), an anode metal layer (Figure 4A), or an anode passivation layer (Figure 3B). Preferably, the cap covers the anode metal as shown in Figures 4A and 3B. When the cap is provided on the anode metal layer or an anode passivation layer, the anode metal 30 beneath the cap 50 can act as a buffer to compensate for potential anode metal losses that occur during battery operation.

[0104] With respect to the passivation layer 10 and the anode passivation layer 40, the cap 50 is preferably functionally thin to minimize the overall contribution of insulating material per unit volume while significantly reducing electron conduction to the top of the scaffolding element. Typically, the capping layer 50 has a thickness in the range of 5 to 200 nm, for example, 10 to 100 nm or 10 to 50 nm, thereby the thickness of the high-k dielectric composition (e.g., k > 10) may be advantageously at the lower end of that range, for example, 5 to 20 nm or 5 to 10 nm.

[0105] In further embodiments, the electrode 1 further comprises an electrolyte. Figure 5B shows an embodiment comprising an electrolyte 60 covering the scaffolding element 4. The shown embodiment also includes a conformal stack of functional layers, including a seed layer 20, an anode metal layer 30, and an anode passivation layer 40 (represented by a single layer for clarity).

[0106] The electrolyte 60 is typically applied to an electrode containing a pre-filled amount of anode metal composition, i.e., to coat an anode metal layer. Preferably, the anode layer is protected by an anode passivation layer to protect the anode composition from reaction with the surroundings. Alternatively, the electrolyte 60 can be applied to an electrode without a pre-filled amount of anode metal 30 and an anode passivation layer 40. In such a case, the anode composition can be plated from the electrolyte onto the scaffolding element by an in-situ plating process. The electrolyte 60 may be a so-called semi-solid electrolyte containing a solid electrolyte layer, a liquid electrolyte, or mobile ions, e.g., ionic liquids and / or ions dissolved in a suitable solvent and dispersed in a solid matrix, e.g., a polymer network (e.g., a gel) or a porous ceramic network. Solid or semi-solid electrolytes may be particularly preferred in embodiments in which one or more subsequent layers are deposited on top of the electrolyte. The electrode configuration of the present disclosure, which includes an essentially closed passivation layer, advantageously allows or enables the application of semi-solid electrolytes or electrolytes that, even if liquid, have relatively higher ion mobility than their solid counterparts.

[0107] In some embodiments, for example, as shown, the electrolyte fills the remaining elongated interspace region between the scaffolds. Alternatively, a solid or semi-solid electrolyte can be provided as a conformal cover layer covering the scaffolds, thereby providing a subsequent battery layer for the remaining interspace region. In a preferred embodiment, the subsequent battery layer includes an electrolyte having relatively high ionic conductivity, such as a liquid electrolyte, to improve ion diffusion within the structure.

[0108] It will be understood that the electrolyte 60 may also be optionally provided as a planar layer in conjunction with the analyte composition, for example, in embodiments where the electrodes are configured as a planar 2D anode having a 3D current collector with integrated electrodes, as shown in Figure 2A (right).

[0109] Further embodiments relate to energy storage devices, such as lithium metal batteries, comprising the electrode 1 disclosed herein. Advantageously, the electrode can be used on one or more of the cathode and anode sides of the energy storage device.

[0110] Figure 6A schematically illustrates an exploded side view of a battery 100 comprising the electrode 1 disclosed herein. In one embodiment, for example, as shown, the electrode is provided on the anode side of the battery. The cathode side may be a conventional cathode 120 comprising a current collector and a cathode composition. Alternatively or in addition, electrode 1 may also be used on the cathode side of the battery by providing, for example, a cathode composition on and / or between upright scaffolding elements 4. In embodiments in which electrode 1 is used as a current collector on the anode side for energy storage applications, the passivation layer 10 equally protects the underlying carbon nanotubes. Obviously, the seed layer and anode passivation layer are omitted.

[0111] A separator 110 provided between the anode and cathode physically separates the cathode from the anode, preventing short circuits while enabling ion transport. The separator 110 may consist of, or essentially consist of, an electrolyte layer, for example, a solid or semi-solid electrolyte layer as described in relation to Figure 5B. Alternatively or in addition, the separator may be provided as a porous carrier structure containing a liquid electrolyte composition. To improve wetting and ion transport, a cathode liquid composition may be provided at the interface between the cathode and the cathode side of the separator 110, respectively. Alternatively or in addition, an anode liquid composition may be provided at the opposing interface between the anode and the anode side of the separator. In a preferred embodiment, the energy storage device comprises a composite solid electrolyte membrane separating the anode and cathode. As described, the anode and / or cathode may be provided as a planar 2D electrode having an integrated current collector. Alternatively, at least one, or optionally both, of the anode and cathode may be configured as a 3D electrode comprising a conformal stack of battery multilayer films.

[0112] Figures 6B and 6C illustrate further embodiments of the electrodes disclosed herein, comprising a particulate anode / cathode composition containing a plurality of discrete particles of the anode / cathode composition. The particulate anode / cathode composition fills the interspatial structure between adjacent upright scaffolding elements 4. An electrically and / or ionically conductive matrix may be provided to electrically contact the particulate anode / cathode composition. Advantageously, the particulate anode / cathode composition may be deposited following, for example, the deposition of a passivation layer 10 from a slurry containing a volatile carrier liquid. Figure 6B illustrates an embodiment in which electrode 1 is configured as an anode, thereby the interspatial structure 5i between adjacent scaffolding elements filled with particles contains or essentially consists of an anode metal composition 30c, e.g., Li. Advantageously, the scaffolding elements 4 may include a seed layer 20 (not shown) to improve the uniformity of the anode metal plating during battery cycling. Figure 6C illustrates an embodiment in which electrode 1 is configured as a cathode, thereby the interspatial structure 5i between adjacent scaffolding elements filled with particles comprises or essentially consists of the cathode composition 120c. With respect to the anode, the carbon-based projection 6 is protected from direct contact with the cathode material and / or electrolyte by a passivation layer 10-2. In contrast to the anode-side application, the passivation layer 10-2 is preferably composed of or essentially consists of aluminum 10-2c.

[0113] Further embodiments relate to methods for manufacturing electrodes disclosed herein. As schematically shown in Figure 7A, Method 200 includes the steps of: providing a 3D composite substrate current collector having a conductive substrate current collector comprising a plurality of laterally dispersed structures of aggregated carbon nanotubes oriented mostly parallel to the direction away from the substrate; and forming a plurality of laterally dispersed conductive scaffold elements having upright sidewalls by coating the aggregated carbon nanotube structures with a passivation layer of the first composition to shield the carbon nanotubes from direct contact with an electroactive material (e.g., an anode metal) while enabling electron transport between the aggregated carbon nanotube structures and the carbon nanotubes. The aggregated tube structures can be suitably coated with the first composition using known dry deposition methods, including but not limited to physical deposition (PVD) methods such as atomic layer deposition (ALD), spatial atomic layer deposition (sALD), and such ionized physical deposition (iPVD). ALD-based methods can advantageously form a conformal cover layer that encapsulates underlying carbon nanotubes after only a few deposition cycles, e.g., >5 deposition cycles, resulting in a thin passivation layer (<5 nm) that is also suitable for materials conventionally considered to be electrical insulators (e.g., SiOx and AlOx). Optionally, following the deposition of the first composition, a reduction step may be performed, for example, under a hydrogen atmosphere, to at least partially convert (reduce) the composition, e.g., ZnO, to a relatively more conductive metallic form. Alternatively or in addition, the passivation layer, particularly the SEI-based first composition, may be provided by wet deposition methods, including but not limited to electroplating.

[0114] If any intermediate layer is provided between the scaffolding element 4 and the substrate 3, such a layer may be applied to the substrate before using the same techniques that can be used to coat the scaffolding element with a passivation layer, i.e., before using known dry deposition methods including, but not limited to, atomic layer deposition (ALD), spatial atomic layer deposition (sALD), and physical deposition (PVD) such as ionized physical deposition (iPVD).

[0115] Following the deposition of the passivation layer 210, the process may then include a step 220 of depositing a seed layer on the formed upright scaffold elements. The seed layer can be conveniently deposited directly on the passivation layer by the dry deposition method described above.

[0116] In some embodiments, the method includes step 230 of directly depositing an anode metal layer, preferably onto a formed seed layer. The anode metal layer may be deposited by known methods, including but not limited to dry deposition methods such as ALD and PVD, and wet deposition methods such as electroplating. Alternatively, the anode or cathode composition may be deposited as particles from a slurry containing a preferably volatile carrier solvent, as shown in Figure 6B.

[0117] In some preferred embodiments, the method further includes step 240 of coating an anode metal layer or particles with an anode passivation layer. The anode passivation layer can be optionally followed or combined with a reduction step (e.g., with hydrogen) to reduce the formed oxide back to a metal composition, and provided by a dry deposition method.

[0118] In other or further preferred embodiments, the method includes step 250 of covering the top of the upright scaffolding element with an electrically insulating cap. The cap can preferably be provided by a dry deposition method, e.g., by physical deposition at a shallow angle to reduce the deposition of the insulator along the base of the structure, or by ALD, thereby controlling the device by de-exposing the structure (e.g., temporarily and / or concentrated) for complete conformal covering of the scaffolding element, for example, to limit deposition on the top of the scaffolding element. In some embodiments, for example, as shown in Figures 7A and 3B, the cap is provided after providing the anode passivation layer. Alternatively or in addition, the cap may be provided between steps 230 and 240 (e.g., as shown in Figure 4A), between steps 220 and 230 (e.g., as shown in Figure 4B), or between steps 210 and 220, i.e., directly on the formed upright scaffolding element.

[0119] A conductive substrate current collector having a plurality of laterally dispersed structures of aggregated carbon nanotubes oriented mostly parallel to the direction away from the substrate can be formed by methods known in the art, including micropatterning of high-density carbon nanotube structures. In a preferred embodiment, forming a plurality of laterally dispersed structures of aggregated carbon nanotubes oriented mostly parallel to the direction away from the substrate includes step 202 of growing carbon nanotubes from a buffer layer provided along the surface of the conductive substrate current collector, the buffer layer including an oxide layer and a dispersed catalyst or seed particles for growing the carbon nanotubes. After growing the carbon nanotubes, aggregated structures of carbon nanotubes can be formed by step 203 of agglomerating the formed forest of individual carbon nanotubes into condensed aggregated structures by known methods, such as thermal agglomeration and capillary agglomeration, for example, by exposure to a volatile solvent followed by evaporation of the solvent.

[0120] The degree of aggregation (DOA) can be characterized as the percentage of voids between adjacent carbon nanotubes within a structure relative to the initial void ratio (i.e., before densification). Here, DOA = 0% corresponds to a non-aggregated state with 100% void ratio (vacuum-acquired nanotubes during growth). Therefore, in preferred embodiments, the DOA is at least 5%, preferably >20%, most preferably greater, for example, >40%, or even above 60%. The smaller the remaining void ratio within the aggregated structure, the greater the integrity of the structure, and the larger the volume fraction of the active material within the device.

[0121] To control the dimensions and spacing of the carbon nanotube structure, the method may include step 201 of patterning the buffer layer by a micropatterning method such as mask lithography.

[0122] Specifically, if the protrusions are polymer protrusions, the manufacturing method may include corresponding polymer processing methods known in the art. Preferred methods include, but are not limited to, photolithography patterning, (micro)imprinting, and (screen)printing, as well as subtractive and / or additive methods. In one embodiment, providing polymer protrusions may include the steps of coating a substrate with one or more suitable precursors, e.g., a crosslinkable polymer layer; then mechanically structuring the coating by, for example, applying a suitablely structured mold or stamp; curing the structured coating by, for example, photocuring heat; removing the mold or stamp; and leaving a 3D structured coating on the substrate. Optionally, the method may include, for example, the removal of residual layers at the bottom of the structure (between the protrusions) by wet or dry etching.

[0123] Figure 7B (left) schematically illustrates a partial top view of a conductive substrate current collector 3 including a patterned buffer layer 7B having individual vertically oriented carbon nanotubes 7 grown therefrom before aggregation. Figure 7B (right) illustrates the same area after capillary aggregation. As shown, the carbon nanotubes aggregate in a hexagonal arrangement of wall segments with relatively high density of carbon nanotubes per unit area (a significant reduction in the gap volume between adjacent carbon nanotubes). Naturally, the aggregation method can be used to fabricate a wide range of structures beyond the embodiments depicted.

[0124] For the purpose of clarity and concise explanation, features are described herein as part of the same or distinct embodiments; however, it will be understood that the scope of the invention may include embodiments having all or some combinations of the described features.

[0125] In interpreting the attached claims, it should be understood that the word “comprising” does not exclude the existence of other elements or actions other than those enumerated in the given claims, the word “a” or “an” preceding an element does not exclude the existence of multiple such elements, any reference numerals in the claims do not limit their scope, some “means” may be represented by the same or different items or implemented structures or functions, and the disclosed devices or parts thereof may be combined together or separated into further parts unless otherwise specifically stated. Where one claim refers to another, this may indicate a synergistic benefit achieved by the combination of their respective features. However, the mere fact that certain measures are enumerated in different claims does not mean that combinations of these measures cannot be used to their advantage. Thus, this embodiment may include all functional combinations of claims, where each claim may, in principle, refer to any prior claim unless explicitly excluded by context. [Explanation of Symbols]

[0126] 1 electrode 2 3D composite current collector 3 Conductive substrate current collector 3-1, 3-2 Copper film 3-1, 3-2 layers 3c Flexible polymer carrier film 4. Conductive upright scaffolding elements 5 side wall 5i Interspace structure 6 protrusions 6b Base of the pillar 6t Pillar tip 6p pillar 7. Aggregated carbon nanotubes 7i internal volume 7B Buffer layer 10 Passivation Layer 10a Metal base layer 10b Cover layer 10c First composition 10p portion 20 Seed Layer 20c composition 30 Alkali metal anode layer 30c Anode Metal Composition 40 Anode Passivation Layers 40c Passivation Composition 50 Electrical Insulation Caps 50c insulating composition 60 electrolytes 100 batteries 110 Separator 120 Cathode 120c Cathode Composition 200 ways 201 Steps 202 steps 203 steps 205 steps 210 steps 220 steps 230 steps 240 steps 250 steps s5 Top section s7 height w1 separation w2 cross section separation

Claims

1. Electrode (1), A 3D composite current collector (2) is provided, which includes a conductive substrate current collector (3) having a plurality of laterally dispersed conductive upright scaffolding elements (4), The aforementioned scaffolding element (4) A polymer-based protrusion (6) extending in a direction away from the base of the substrate, An electrode (1) comprising: a passivation layer (10) covering the upright sidewalls including the tips of polymer-based protrusions to shield the polymer-based protrusions from direct contact with electrode material and / or electrolyte material, wherein the passivation layer (10) is composed of a first composition (10c) that enables electron transport to the substrate and is resistant to the transport of alkali metals and alkali metal ions across the passivation layer.

2. The electrode according to claim 1, wherein the polymer-based protrusion tapers toward the tip.

3. The electrode according to any one of the prior claims, wherein the passivation layer (10) includes a metal layer, the metal layer optionally includes portions that extend along the surface of the substrate, thereby interconnecting adjacent conductive upright scaffolding elements.

4. The electrode according to any one of the prior claims, wherein the passivation layer (10) includes a layer of semiconductor ceramic.

5. The electrode according to any one of the prior claims, wherein the passivation layer (10) is a laminate, and the laminate comprises a metal layer according to claim 3, the metal layer including a portion extending along the surface of the substrate that interconnects adjacent conductive upright scaffolding elements, and a layer of semiconductor ceramic according to claim 4 provided on the metal layer, wherein the semiconductor material has lower conductivity than the metal layer, and thereby the layer of semiconductor ceramic does not interconnect adjacent conductive upright scaffolding elements.

6. The electrode according to claim 4 or 5, wherein the thickness of the semiconductor ceramic layer along the upright side wall increases in the direction toward the tip.

7. The electrode according to any one of the prior claims, further comprising a sub-layer extending between the projection and the passivation layer (10), wherein the sub-layer is made of an electrical insulator and adjacent conductive upright scaffolding elements are not interconnected.

8. The electrode according to any one of the prior claims, wherein the first composition (10c) comprises a metal or metal alloy selected from Cu, Ni, Al, Ti, and alloys thereof.

9. The electrode according to any one of the prior claims, wherein the first composition (10c) includes an electrical insulator having a thickness and resistivity configured to form a tunnel junction.

10. The electrode according to any one of the prior claims, further comprising an intermediate layer between the scaffolding element (4) and the substrate current collector (3), wherein the intermediate layer is chemically inert with respect to the substrate current collector (3).

11. The electrode according to any one of the prior claims, wherein the electrode (1) further comprises a seed layer (20) that at least partially covers the outer surface of the scaffolding element (4) for receiving an anode metal composition (30c), and the seed layer (20) comprises a composition (20c) selected for alloying with an alkali anode metal.

12. The electrode according to any one of the prior claims, further comprising an alkali metal anode layer (30) covering the plurality of scaffolding elements (4).

13. The electrode according to claim 12, further comprising an anode passivation layer (40) covering the alkali metal anode layer (30).

14. The electrode according to claim 13, wherein the anode passivation layer (40) comprises a metal or metalloid composition (40c) that alloys with the alkali metal.

15. The electrode according to any one of the prior claims, further comprising an electrical insulating cap (50) that covers the top portion (s4) of the scaffolding element (4).

16. The electrode according to claim 15, wherein the electrical insulating cap (50) is provided on the anode passivation layer (40), between the anode metal layer (30) and the anode passivation layer (40), or on the seed layer (20).

17. The electrode according to any one of the prior claims, further comprising an electrolyte (60) covering the scaffolding element (4).

18. The electrode according to any one of the prior claims, further comprising particles of an anode or cathode material (30c, 120c).

19. The electrode according to any one of the prior claims, wherein the scaffolding element has an aspect ratio in the range of 1:1 to 20:1, defined by dividing the height by its width.

20. The electrode (1) according to any one of the prior claims, wherein the conductive substrate (3) is provided as a flexible metal foil or as a metal-coated flexible carrier.

21. The electrode (1) according to any one of the prior claims, wherein the laterally dispersed conductive upright scaffolding elements are segmented into sectors having lateral separation aligned according to the substrate bending axis.

22. The electrode (1) according to any one of the prior claims, wherein the conductive substrate (3) is provided with each of the scaffolding elements (4-1, 4-2) on both sides.

23. An energy storage device (100) comprising an electrode (1) as described in any one of the prior claims.

24. The energy storage device according to claim 23, wherein the storage device comprises a composite solid electrolyte membrane that separates the opposing anode and cathode sides of the storage device.

25. A method for manufacturing an electrode according to any one of claims 1 to 22, To provide a 3D composite substrate current collector (2), wherein the 3D composite substrate current collector (2) has a conductive substrate current collector (3) having a plurality of laterally dispersed polymer-based protrusions extending in a direction away from the base of the substrate, A method comprising coating the upright sidewalls, including the tips of the polymer-based protrusions, with a passivation layer (10) made of a first composition (10c) that enables electron transport to the substrate and is resistant to the transport of alkali metals and alkali metal ions across the passivation layer.

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