U.S. patent application number 16/631767 was filed with the patent office on 2020-06-11 for forming a layer of functional material on an electrically conductive substrate.
The applicant listed for this patent is IMEC VZW Katholieke Universiteit Leuven, KU LEUVEN R & D. Invention is credited to Philippe M. Vereecken, Stanislaw Piotr Zankowski.
Application Number | 20200181789 16/631767 |
Document ID | / |
Family ID | 59366291 |
Filed Date | 2020-06-11 |
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United States Patent
Application |
20200181789 |
Kind Code |
A1 |
Zankowski; Stanislaw Piotr ;
et al. |
June 11, 2020 |
Forming a Layer of Functional Material on an Electrically
Conductive Substrate
Abstract
At least one embodiment relates to a method for forming a layer
of functional material on an electrically conductive substrate. The
method includes depositing an interlayer on the substrate. The
interlayer includes a transition metal oxide, a noble metal, or a
noble-metal oxide. The interlayer has a thickness between 0.5 nm
and 30 nm. The method also includes depositing a functional
material precursor layer on the interlayer. Further, the method
includes activating the functional material precursor layer by
annealing to form the layer of functional material.
Inventors: |
Zankowski; Stanislaw Piotr;
(Leuven, BE) ; Vereecken; Philippe M.; (Leuven,
BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IMEC VZW
Katholieke Universiteit Leuven, KU LEUVEN R & D |
Leuven
Leuven |
|
BE
BE |
|
|
Family ID: |
59366291 |
Appl. No.: |
16/631767 |
Filed: |
July 10, 2018 |
PCT Filed: |
July 10, 2018 |
PCT NO: |
PCT/EP2018/068674 |
371 Date: |
January 16, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/0407 20130101;
C25D 11/045 20130101; B82Y 30/00 20130101; C25D 3/12 20130101; C25D
11/18 20130101; C25D 9/06 20130101; H01M 4/045 20130101; C23F 1/28
20130101; C25D 11/10 20130101; H01M 4/0442 20130101; C25D 11/34
20130101; H01M 4/86 20130101; C23F 1/00 20130101; H01M 4/661
20130101; C25D 9/02 20130101; H01M 4/0404 20130101; B82Y 40/00
20130101; C23C 2222/20 20130101; C25D 11/12 20130101; H01M 4/72
20130101; H01M 4/0452 20130101; H01M 4/0471 20130101; H01M 4/80
20130101; H01M 8/0232 20130101; C23F 1/20 20130101; C25D 11/024
20130101; C25D 1/006 20130101; C25D 11/24 20130101; H01M 8/0247
20130101 |
International
Class: |
C25D 1/00 20060101
C25D001/00; H01M 4/66 20060101 H01M004/66; H01M 8/0232 20060101
H01M008/0232; H01M 8/0247 20060101 H01M008/0247; C25D 11/04
20060101 C25D011/04; C25D 11/10 20060101 C25D011/10; C25D 11/34
20060101 C25D011/34; C25D 9/06 20060101 C25D009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2017 |
EP |
17181782.8 |
Claims
1. A method for forming a layer of functional material on an
electrically conductive substrate, the method comprising:
depositing an interlayer on the substrate, wherein the interlayer
comprises a transition metal oxide, a noble metal, or a noble-metal
oxide, and wherein the interlayer has a thickness between 0.5 nm
and 30 nm; depositing a functional material precursor layer on the
interlayer; and activating the functional material precursor layer
by annealing to form the layer of functional material.
2. The method according to claim 1, wherein depositing the
functional material precursor layer comprises depositing an
electrode material precursor layer, and wherein activating the
functional material precursor layer comprises annealing in the
presence of an ion containing precursor to form a layer of active
electrode material.
3. The method according to claim 1, wherein depositing the
functional material precursor layer comprises anodic
electrodeposition.
4. The method according to claim 1, wherein the electrically
conductive substrate is a transition metal substrate.
5. The method according to claim 1, wherein the electrically
conductive substrate is a three-dimensional substrate comprising a
plurality of electrically conductive structures being aligned
longitudinally along a first direction.
6. The method for forming a layer of functional material according
to claim 5, wherein the electrically conductive substrate further
comprises a plurality of electrically conductive interconnecting
structures oriented along a second direction different from the
first direction.
7. The method according to claim 1, wherein the interlayer
comprises a transition metal oxide, and wherein depositing the
interlayer comprises electrodeposition in a solution having a pH
between 7 and 12.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a national stage entry of
PCT/EP2018/068674 filed Jul. 10, 2018, which claims priority to EP
17181782.8 filed on Jul. 18, 2017, the contents of each of which
are hereby incorporated by reference.
FIELD
[0002] The present disclosure relates to methods for forming a
layer of active electrode material on an electrically conductive
substrate, such as for example on a three-dimensional metal
substrate comprising a plurality of electrically conductive
(nano)structures.
BACKGROUND
[0003] Solid-state batteries, and more in particular thin-film
solid-state batteries are attractive energy storage devices.
Solid-state batteries are based on solid-state battery cells
typically comprising a stack of a first current collector layer, a
first electrode layer (e.g. a positive active material layer or
cathode layer), a solid electrolyte layer, a second electrode layer
(e.g. a negative active material layer or anode layer), and a
second current collector layer. The batteries may further be
encapsulated, such as for example in a polymer package.
[0004] In the example of solid-state Li ion insertion battery
cells, the current collector layers may comprise a metal foil, such
as a foil of aluminum, nickel, or copper and the active cathode
layer may for example comprise lithiated transition metal oxides or
salts, such as lithium manganese oxide (LMO), lithium cobalt oxide
(LCO), or lithium iron phosphate (LPO). The anode layer may for
example comprise carbon, silicon, spinel lithium titanium oxide
(LTO), or metallic lithium. The solid-state electrolyte may
comprise glassy, ceramic, crystalline, or polymer
lithium-containing materials. Due to the high electric and ionic
resistivity of the active materials, the anode and cathode layer
thicknesses are limited to less than 5 micrometers. This results in
a limited energy and power density of the thin film solid-state
battery cells.
[0005] To overcome these limitations, three-dimensional electrode
structuring has been proposed to increase the surface area of the
electrodes, thus increasing the amount of the active materials
present in a unit area of a battery cell. In such three-dimensional
approaches, one of the main manufacturing challenges is conformal
coating of battery materials on the three-dimensional electrode
surfaces. Another challenge is the need for advanced, low-cost
methods for manufacturing the three-dimensional electrode
structures.
[0006] A three-dimensional electrode structure may for example
comprise or consist of a plurality of electrically conductive
nanowires oriented along a same direction and being closely spaced,
for example with a spacing between neighboring nanowires smaller
than the nanowire length, such as for example a spacing that is a
factor of 1.2 to 10 smaller than the nanowire length. A relatively
cheap method for manufacturing such plurality of electrically
conductive nanowires comprises electroplating of a metal in a
porous anodic aluminum oxide (AAO) template formed by anodization
of an aluminum foil. Up to 100 micrometer thick porous aluminum
oxide templates can be produced. However, the pores or channels of
the templates produced by anodization of aluminum foils are always
covered with an insulating aluminum oxide barrier layer having a
thickness of tens to hundreds of nanometers. This barrier layer may
be removed from the channel bottoms to enable subsequent formation
of the plurality of electrically conductive nanowires by
electroplating.
[0007] Various methods may be used to remove the barrier layer from
the channel bottoms, without separation of the template from the
underlying remaining part (non-anodized part) of the aluminum foil.
For example, the voltage used in the anodization process may be
gradually reduced during the final stage of anodization. This
results in a reduction of the interpore distance and of the pore
size at a bottom of the channels, with a barrier layer of smaller
thickness, for example 1 nm or less. Such barrier layer thickness
is sufficiently small to allow electroplating of a metal inside the
channels or pores. However, this approach results in nanowires
poorly connected to the substrate, through long (hundreds of
nanometers long) root-like, thin (a few nm in diameter) nanowires.
This may result in poor mechanical stability of the nanowires
network, prone to delamination from the substrate.
[0008] Another method for removing the barrier layer from the
channel bottoms of the template comprises thinning the barrier
layer by immersing the template in an H.sub.3PO.sub.4 solution that
slowly etches the barrier layer. This, however, results in
excessive pore widening, resulting in nanowires formed in such a
template that have a rather large diameter and that fill most of
the volume. This limits the volume remaining available for the
active electrode material to be coated thereon, eventually limiting
the energy density of the electrode.
[0009] Yet another method for removing the barrier layer from the
channel bottoms of the template comprises separation of the
template from the underlying remaining part (non-anodized part) of
the aluminum foil. According to this method, the aluminum foil is
removed, e.g. dissolved, after formation of the porous template.
This results in a fragile, free-standing template with an exposed
barrier layer at one side and open pores at another side. The
exposed barrier layer is then removed, for example by single-side
etching in a diluted H.sub.3PO.sub.4 solution, and a thin metal
layer is deposited to act as a working electrode for subsequent
electrodeposition of metallic nanowires in the template. However,
the fragility of the free-standing template makes this method hard
to implement in large-scale manufacturing.
[0010] Hence, there is a need for a method that allows removing the
barrier layer from the channel bottoms of a porous anodic template
for subsequent formation therein of a plurality of spaced nanowires
e.g. by electroplating, wherein pore widening is avoided at one
hand, wherein pore narrowing is avoided on the other hand, and
wherein the method is suitable for implementation in large-scale
manufacturing.
[0011] In a method for fabricating solid-state batteries having a
three-dimensional electrode structure, there is a need for forming
an active electrode material layer on the three-dimensional
electrode structure. The active electrode material layer may be
formed by a process that allows conformal deposition. A method that
can be used is electroplating. For example, in case of Li ion
insertion electrodes, manganese oxide (MnO.sub.x with
1.ltoreq.x.ltoreq.2) may be used as a cathode precursor material,
which is then further transformed into an active lithium manganese
oxide (LMO) electrode material upon conversion with lithium
(lithiation).
[0012] In the large-scale manufacturing of commercial batteries, a
hot acidic bath containing MnSO.sub.4 and H.sub.2SO.sub.4 is
typically used for the synthesis of MnO.sub.x. However, due to the
acidic nature of the bath, electrodeposition cannot be carried out
on most metals, due to their inherent oxidation and dissolution in
an acidic environment upon application of an anodic current. The
only metals suitable for anodic deposition of MnO.sub.2 from acidic
baths are the noble metals such as Pt or Au or metals forming a
stable, dense passive oxide layer on their surface, such as
titanium. However, these metals are either very expensive (noble
metals) or very difficult to electrodeposit (titanium).
[0013] Other methods for the fabrication of manganese oxide cathode
precursors use neutral manganese baths based on organic complexes
of Mn.sup.2+, such as acetates or citrates. These baths, having a
pH close to 7, can be used to electroplate MnO.sub.x precursors on
less noble metals, such as Ni. However, due to the near-neutral pH
of such baths and due to the presence of dissolved oxygen, these
solutions are not stable and, upon time, MnO.sub.x precipitates are
formed in the bath. This substantially limits the applicability of
these baths for large-scale manufacturing, where stability of the
baths is important from an economical and industrial point of view.
The change in the composition of the bath may also lead to changes
in electroplating kinetics, resulting in poor reproducibility.
[0014] Further, in a method for fabricating solid-state batteries
an annealing step (lithiation step) is typically done after
deposition of the cathode precursor material on the electrode
structure, to thereby activate (lithiate) the cathode precursor
material and form an active (lithiated) cathode material. When
using a non-noble metal such as for example a transition metal for
forming the electrode structure, such annealing step may lead to
thermal degradation (e.g. due to oxidation or another chemical
reaction) of the electrode structure.
[0015] Hence, there is a need for a method that allows forming a
layer of active electrode material on a broad range of metals,
wherein the method may be a low-cost process suitable for
large-scale manufacturing and wherein the method allows
substantially conformal deposition. Further, there is a need for a
method with a reduced risk of degradation of the electrode material
during subsequent processing, such as annealing.
SUMMARY
[0016] Some embodiments of the present disclosure provide methods
that allow conformally forming a layer of a functional material
such as an active electrode material on a broad range of metals or
metal substrates, including for example transition metal
substrates, e.g. three-dimensional transition metal substrates
comprising a plurality of spaced (nano)structures, wherein the
methods enable reproducible, conformal deposition of the functional
material layer, and wherein degradation, such as for example
oxidation, of the metal during (subsequent) processing, such as
annealing, is substantially reduced.
[0017] The above is at least partially accomplished by a method
according to the present disclosure.
[0018] According to a first aspect, the present disclosure is
related to a method for transforming at least part of a valve metal
layer into a template comprising a plurality of spaced channels
aligned longitudinally along a first direction. A method according
to the first aspect of the present disclosure comprises a first
anodization step anodizing at least part of the valve metal layer
in the thickness direction and thereby forming a porous layer of
valve metal oxide comprising a plurality of channels, each channel
having channel walls aligned longitudinally along the first
direction and having a channel bottom, the channel bottoms being
coated with a first insulating metal oxide barrier layer as a
result of the first anodization step; next a protective treatment
inducing hydrophobic surfaces to the channel walls and channel
bottoms; a second anodization step after the protective treatment,
thereby substantially removing the first insulating metal oxide
barrier layer from the channel bottoms and inducing anodization
only at the bottoms of the plurality of channels and creating a
second insulating metal oxide barrier layer at the channel bottoms;
and an etching step in an acidic etching solution or in a basic
etching solution, thereby removing the second insulating metal
oxide barrier layer from the channel bottoms. The plurality of
spaced channels may, for example, comprise a plurality of spaced
nanochannels.
[0019] In the context of the present disclosure, a valve metal is a
metal selected from the group of aluminum, tungsten, titanium,
tantalum, hafnium, niobium, vanadium,. and zirconium. In the
context of the present disclosure, a valve metal layer is a layer
comprising a valve metal or a valve metal alloy. A valve metal
layer may be a single layer or it may be a layer stack comprising
at least two valve metal layers. In some embodiments of a method of
the first aspect of the present disclosure, a valve metal layer
comprising a layer of aluminum, an aluminum alloy, titanium, a
titanium alloy, tantalum, or a tantalum alloy may be used.
[0020] In embodiments of a method of the first aspect, performing
the protective treatment may comprise annealing at a temperature in
the range between 300.degree. C. and 550.degree. C.
[0021] In embodiments of a method of the first aspect, performing
the protective treatment may comprise depositing a protective layer
over the channel walls and over the channel bottoms. In such
embodiments, the second anodization step additionally removes the
protective layer only from the channel bottoms.
[0022] Some embodiments of the method of the first aspect of the
present disclosure may allow for the removal of a barrier layer
from the channel bottoms of a template formed by anodization,
wherein the barrier layer can be removed with a limited pore
widening at one hand and with a limited pore narrowing on the other
hand. This results in a template comprising a plurality of spaced
channels having a diameter that is substantially constant along
their entire length, i.e. up to the bottom.
[0023] A limited pore narrowing may allow the formation of a
plurality of structures inside the plurality of channels with
mechanical stability, a limited risk of delamination from an
underlying substrate, and with an electrical and mechanical contact
with the underlying substrate, for example an electrically
conductive underlying substrate.
[0024] A limited pore widening may result in a template comprising
a plurality of spaced channels having a diameter (corresponding to
a final pore diameter) that is smaller than, e.g. substantially
smaller than, a spacing between neighboring channels (wherein the
spacing is defined here as a distance between facing channel
walls). This may allow for the formation of a plurality of
structures inside the plurality of channels of the template that
take in a reduced volume as compared to alternative templates
wherein pore widening results in channels being spaced at a
distance that is typically smaller than their diameter. A plurality
of structures taking in a reduced volume may allow an increased
volume to remain available between the structures, e.g. for
deposition of an additional layer or additional layers. For
example, a plurality of structures formed inside the plurality of
channels may be used as a current collector in electrochemical
devices such as for example electrochemical sensors, batteries,
supercapacitors, fuel cells, (photo)electrolyzers, or chemical
reactors. The increased volume available between the structures may
then, for example, be utilized for providing a layer of functional
material, such as a layer of active electrode material or an
electrolyte material, the present disclosure not being limited
thereto.
[0025] A method of the first aspect of the present disclosure may
be relatively straightforward. It may not require sophisticated
equipment or vacuum equipment and it is therefore potentially
low-cost. It is suitable for implementation in large-scale
manufacturing.
[0026] A method of the first aspect of the present disclosure may
include the use of an anodization based process for forming the
template, which may allow for control of a diameter of the
plurality of spaced channels and a distance between neighboring
channels by controlling a voltage or a current used during
anodization. A method of the first aspect of the present disclosure
may, by the use of an anodization based process for forming the
template, allow for control of a depth of the plurality of spaced
channels by controlling a duration of the first anodization
step.
[0027] In embodiments of a method of the first aspect wherein
performing the protective treatment comprises depositing a
protective layer on the channel walls and on the channel bottoms,
the protective layer may for example comprise hydrophobic silane or
a polymer that is resistant to the etching solution, such as for
example polystyrene, poly(methyl 2-methylpropanoate), or
poly(dimethylsiloxane).
[0028] In embodiments of a method of the first aspect of the
present disclosure the etching solution may be an aqueous solution,
which may allow the template to be formed without the use of
organic solvents, resulting in an environmentally friendly method.
The aqueous etching solution may, for example, be an acidic etching
solution comprising phosphoric acid, sulfuric acid, oxalic acid, or
chromic acid or a combination thereof. Alternatively, the etching
solution may be a basic etching solution e.g. comprising ammonia,
hydrogen peroxide, potassium hydroxide, or a combination
thereof.
[0029] In embodiments of a method of the first aspect, the etching
solution may further comprise a surface tension adjusting agent,
which may, through the surface tension adjusting agent, facilitate
penetration of the etching solution inside the plurality of
channels towards the channel bottoms. The surface tension adjusting
agent may, for example, be selected from ethyl alcohol, isopropyl
alcohol, acetone, and sodium dodecyl sulfate, the present
disclosure not being limited thereto.
[0030] Embodiments of a method of the first aspect of the present
disclosure may further comprise providing ultrasonic waves during
the second anodization step, which may facilitate removal of the
first insulating metal oxide barrier layer and, if present, removal
of the protective layer, from the channel bottoms during the second
anodization step. It may further facilitate removal of the second
insulating metal oxide barrier layer from the channel bottoms
during the etching step. Embodiments of a method of the first
aspect of the present disclosure may comprise providing ultrasonic
waves during the first anodization step. Embodiments of a method of
the first aspect of the present disclosure may comprise providing
ultrasonic waves during both the first anodization step and the
second anodization step.
[0031] In embodiments of a method of the first aspect of the
present disclosure, the first anodization step may anodize only a
part of the valve metal layer in the thickness direction, to
thereby form the template and defining a substrate supporting the
template, wherein the substrate comprises a remaining, non-anodized
part of the valve metal layer. This may allow the formation of
templates from a free-standing metal layer such as a free-standing
metal foil, e.g. a free-standing aluminum foil. In such
embodiments, the need for providing a separate substrate supporting
the valve metal layer may be reduced, which may lead to a reduced
cost. Using a free-standing layer of metal may allow anodization of
the layer at two opposite sides or surfaces, thus allowing the
formation of a stack comprising a first porous layer of valve metal
oxide (first template), a non-anodized valve metal layer
(substrate) and a second porous layer of valve metal oxide (second
template). Such a stack comprising a first template and a second
template at opposite substrate sides may, for example, be used for
forming a plurality of spaced (nano)structures in a fabrication
process of solid-state batteries comprising a stack of battery
cells. In such embodiments, a single substrate may provide support
for nanostructures (the nanostructures e.g. having the function of
a current collector) at both sides of the substrate, thus reducing
the volume occupied by substrate material per battery cell.
[0032] In other embodiments of a method of the first aspect of the
present disclosure the valve metal layer may be provided on an
electrically conductive substrate. In this context, "electrically
conductive substrate" also includes any substrate comprising an
electrically conductive layer at an exposed surface thereof. In
such embodiments, the first anodization step may anodize the valve
metal layer throughout the layer in the thickness direction, to
thereby form a porous layer of valve metal oxide comprising a
plurality of channels, each channel having channel walls aligned
longitudinally along the first direction and having a channel
bottom, the channel bottoms being located at an interface between
the valve metal layer and the underlying electrically conductive
layer or substrate. In such embodiments, the etching step exposes
the electrically conductive layer at the channel bottoms. The
electrically conductive layer may for example be a titanium nitride
layer, a titanium layer, a nickel layer, an indium tin oxide layer,
a gold layer, or a platinum layer, the present disclosure not being
limited thereto.
[0033] According to a second aspect, the present disclosure is
related to a template comprising a plurality of spaced channels
aligned longitudinally along a first direction, wherein the
template is obtainable by a method according to an embodiment of
the first aspect of the present disclosure.
[0034] In general, features of the second aspect of the present
disclosure provide similar features as discussed above in relation
to the first aspect of the present disclosure.
[0035] Embodiments of the template of the second aspect of the
present disclosure may allow the plurality of spaced channels to
have a diameter that is substantially constant along their entire
length, i.e. up to the bottom, and that they may have a channel
bottom free of any barrier layer, i.e. exposing an underlying
substrate. This may allow the formation of a plurality of
structures inside the plurality of channels with mechanical
stability, a limited risk of delamination from an underlying
substrate, and with an electrical and mechanical contact with the
underlying substrate, for example an electrically conductive
underlying substrate.
[0036] Some embodiments of the template of the second aspect of the
present disclosure may allow the plurality of spaced channels to
have a diameter that is smaller than, e.g. substantially smaller
than, a spacing between neighboring channels (wherein the spacing
is defined here as a distance between facing channel walls). This
may allow the formation of a plurality of structures inside the
plurality of channels of the template that take in a reduced volume
as compared to alternative templates wherein pore widening results
in channels being spaced at a distance that is typically smaller
than their diameter. When a plurality of structures takes in a
reduced volume, an increased volume may remain available between
the structures, e.g. for deposition of an additional layer or
additional layers. For example, a plurality of structures formed
inside the plurality of channels may be used as a current collector
in electrochemical devices such as electrochemical sensors,
batteries, supercapacitors, fuel cells, (photo)electrolyzers,. or
chemical reactors. The increased volume available between the
structures may then for example be utilized for providing a layer
of functional material, such as for example a layer of active
electrode material or an electrolyte material, the present
disclosure not being limited thereto.
[0037] In embodiments of a template of the second aspect of the
present disclosure, the first direction may be at an angle in the
range between 60.degree. and 90.degree., for example between
80.degree. and 90.degree., with respect to a surface of the valve
metal layer from which the template is formed. For example, the
first direction may be substantially orthogonal to a surface of the
valve metal layer.
[0038] In embodiments of a template of the second aspect of the
present disclosure, the template may further comprise a plurality
of interconnecting channels oriented along a second direction
different from the first direction, wherein the interconnecting
channels form a connection between neighboring spaced channels
oriented along the first direction. The second direction may for
example be substantially orthogonal to the first direction. A
template comprising such interconnecting channels may allow for the
formation of a plurality of interconnected structures inside the
plurality of channels of the template. Such plurality of
interconnected structures may for example form a mesh-shaped
structure.
[0039] According to a third aspect, the present disclosure is
related to a method for forming a plurality of spaced structures on
a substrate. A method according to the third aspect of the present
disclosure comprises transforming at least part of a valve metal
layer into a template comprising a plurality of spaced channels
aligned longitudinally along a first direction according to an
embodiment of the first aspect of the present disclosure, thereby
forming the template and defining the substrate, and depositing a
solid functional material within the channels of the template to
thereby form the plurality of spaced structures inside the
plurality of spaced channels. This results in a plurality of spaced
structures being aligned longitudinally along the first direction.
The method may further comprise removing the template by etching.
Examples of spaced electrically conductive structures that may be
formed using a method of the third aspect of the present disclosure
are pillars, nanopillars, wires, nanowires, tubes (or "hollow"
wires), nanotubes, meshes, and nanomeshes.
[0040] In the context of the third aspect of the present
disclosure, a functional material or functional material layer is a
material or material layer that satisfies or provides a defined
functionality and/or has defined properties, adjusted for a device
in which it is integrated.
[0041] In embodiments of a method of the third aspect of the
present disclosure, depositing the solid functional material within
the channels of the template may comprise depositing an
electrically conductive material, a semiconductor material, an
electrically insulating material,. or a combination thereof.
[0042] In embodiments, depositing the solid functional material
within the channels of the template may comprise filling the
channels with the solid functional material, e.g. completely
filling the channels in a lateral direction orthogonal to the first
direction. In embodiments, depositing the solid functional material
within the channels may comprise depositing a layer of solid
functional material on the channel walls, thereby only partially
filling the channels in a lateral direction with the solid
functional material and leaving openings inside.
[0043] In embodiments of a method of the third aspect of the
present disclosure, depositing the solid functional material within
the channels of the template may comprise depositing an
electrically conductive material by galvanostatic or potentiostatic
electrodeposition or plating, to thereby form a plurality of spaced
electrically conductive structures. In such embodiments, a
low-resistance electrical contact may be established between the
plurality of spaced electrically conductive structures and an
underlying electrically conductive substrate. The electrical
contact may for example have a contact sheet resistance lower than
1 Ohm cm.sup.2.
[0044] In general, features of the third aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0045] A method of the third aspect of the present disclosure may
allow for the formation of a plurality of spaced structures on a
substrate with mechanical stability, a limited risk of delamination
from the underlying substrate, and a mechanical contact with the
underlying substrate. A method of the third aspect of the present
disclosure may allow for the formation of a plurality of spaced
electrically conductive structures with an electrical contact to an
underlying electrically conductive substrate, such as for example
with a contact sheet resistance lower than 1 Ohm cm.sup.2. A method
of the third aspect of the present disclosure may allow for the
formation of a plurality of spaced structures, e.g. electrically
conductive structures, taking in a relatively limited volume,
thereby leaving an increased volume available in between the
plurality of spaced structures, for example for deposition of an
additional layer, e.g. an additional layer of functional material,
such as e.g. a layer of active electrode material.
[0046] A method of the third aspect of the present disclosure it
may be relatively straightforward. It may not require sophisticated
equipment or vacuum equipment and is therefore potentially
low-cost. It is suitable for implementation in large-scale
manufacturing.
[0047] A method of the third aspect of the present disclosure may
allow for control of a diameter and a length (height) of the
plurality of spaced structures, e.g. electrically conductive
structures, and of a distance between neighboring structures. This
may further enable control of the energy density and power density
of a battery cell having a current collector comprising such a
plurality of spaced electrically conductive structures.
[0048] In embodiments of the method of the third aspect of the
present disclosure the electrically conductive material deposited
within the channels of the template to thereby form the plurality
of spaced electrically conductive structures may be a transition
metal, which may result in a reduced cost. This may further allow a
reduction in a cost of battery cells having a current collector
comprising such plurality of spaced electrically conductive
transition metal structures. In embodiments of the third aspect of
the present disclosure the transition metal may for example be
selected from nickel, copper, and chromium.
[0049] According to a fourth aspect, the present disclosure is
related to an entity comprising a substrate with a plurality of
spaced structures thereon, the plurality of spaced structures being
aligned longitudinally along a first direction and being obtainable
by a method according to an embodiment of the third aspect of the
present disclosure.
[0050] In general, features of the fourth aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0051] In embodiments of an entity of the fourth aspect of the
present disclosure the first direction may be at an angle in the
range between 60 and 90, for example between 80 and 90, with
respect to a surface of the substrate. For example, the first
direction may be substantially orthogonal to a surface of the
substrate.
[0052] In embodiments of an entity of the fourth aspect of the
present disclosure, the entity may further comprise a plurality of
interconnecting structures oriented along a second direction
different from the first direction, wherein the interconnecting
structures form a connection between neighboring spaced structures
oriented along the first direction, thereby forming for example a
mesh-shaped structure. The second direction may for example be
substantially orthogonal to the first direction, the present
disclosure not being limited thereto,
[0053] In embodiments of the fourth aspect of the present
disclosure the plurality of spaced structures and, if present, the
plurality of interconnecting structures, may comprise an
electrically conductive material, a semiconductor material, an
electrically insulating material, or a combination thereof.
[0054] According to a fifth aspect, the present disclosure is
related to a device comprising an entity according to the fourth
aspect of the present disclosure. In embodiments of the fifth
aspect of the present disclosure the device may for example be an
electrochemical device, such as e.g. an electrochemical sensor, a
battery, a supercapacitor, a fuel cell, an electrolyzer, a
photo-electrolyzer, or a chemical reactor, the present disclosure
not being limited thereto.
[0055] In general, features of the fifth aspect of the present
disclosure provide similar advantages features as discussed above
in relation to the previous aspects of the present disclosure.
[0056] According to a sixth aspect, the present disclosure is
related to a method for forming a layer of a functional material on
an electrically conductive substrate, such as for example on a
transition metal substrate. A method according to the sixth aspect
of the present disclosure comprises depositing an interlayer on the
substrate, wherein the interlayer comprises a transition metal
oxide, a noble metal, or a noble-metal oxide, and wherein the
interlayer has a thickness in the range between 0.5 nm and 30 nm,
for example in the range between 0.5 nm and 10 nm; depositing a
functional material precursor layer on the interlayer; and
activating the functional material precursor layer by annealing to
thereby form the layer of functional material.
[0057] In embodiments of the method of the sixth aspect of the
present disclosure the layer of functional material may for example
be a layer of active electrode material. In such embodiments
depositing the functional material precursor layer comprises
depositing an electrode material precursor layer. The annealing
step for activating the electrode material precursor layer may be
done in the presence of an ion containing precursor, such as for
example a lithium containing precursor, a sodium containing
precursor, or a magnesium containing precursor, the present
disclosure not being limited thereto. In embodiments of the sixth
aspect of the present disclosure the electrode material may be a
cathode material or an anode material. The functional material
precursor layer may be a layer of cathode precursor material, for
example comprising manganese oxide, manganese dioxide, cobalt
oxide, manganese nickel oxide, or iron phosphate, or it may be a
layer of anode precursor material.
[0058] In general, features of the sixth aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0059] Providing an interlayer in accordance with a method of the
sixth aspect of the present disclosure may result in a reduced risk
of degradation of the underlying electrically conductive substrate
material, such as for example a reduced risk of oxidation of the
electrically conductive substrate material. The electrically
conductive substrate may for example be used as a current collector
of a battery cell. Providing an interlayer in accordance with a
method of the sixth aspect of the present disclosure may result in
a reduced risk of degradation (e.g. oxidation) of the current
collector material, for example under the influence of the step of
activating the layer of electrode precursor material by
annealing.
[0060] Providing an interlayer in accordance with a method of the
sixth aspect of the present disclosure may result in a reduced risk
of degradation of the underlying electrically conductive substrate
material, e.g. current collector material, under the influence of
an electrochemical deposition process, as may for example be used
for depositing the functional material precursor layer. Such
electrochemical deposition process may for example comprise
deposition in an acidic bath, for example for depositing the layer
of electrode precursor material (electrode material precursor
layer), the present disclosure not being limited thereto.
[0061] In embodiments of the sixth aspect of the present disclosure
depositing the functional material precursor layer, e.g. layer of
electrode precursor material, may comprise anodic electrodeposition
from an acidic solution or from a basic solution, which may,
through anodic electrodeposition, provide a low-cost process
suitable for large scale manufacturing. In some embodiments, the
use of an acidic solution may offer stability of the
electrodeposition bath.
[0062] A method of the sixth aspect of the present disclosure may
allow for the formation of a functional material layer, such as a
layer of active electrode material, on a broad range of metals,
including for example relatively cheap transition metals. This
further allows for example reducing a cost of battery cells having
a current collector structure comprising such plurality of spaced
electrically conductive transition metal structures.
[0063] A method of the sixth aspect of the present disclosure may
allow for the conformal formation of a layer of functional material
on a variety of metal substrates, including transition metal
substrates, for example on three-dimensional transition metal
substrates. More in particular, a method of the sixth aspect of the
present disclosure may allow for the conformal formation of a layer
of active cathode material on a variety of metal substrates,
including transition metal substrates, for example on
three-dimensional transition metal substrates. Compared to
fabrication methods wherein an active anode material is formed on a
three-dimensional substrate, this may allow for the fabrication of
solid-state battery cells with an improved energy density and power
density. This is related to a generally lower capacity of cathode
materials as compared to anode materials. Therefore,
three-dimensional structuring of a cathode layer may increase the
capacity, energy density, and/or power density of a battery cell as
compared to an approach wherein only the anode layer is
three-dimensionally structured and not the cathode layer.
[0064] In embodiments of the sixth aspect of the present disclosure
the electrically conductive substrate may be a three-dimensional
substrate comprising a plurality of spaced electrically conductive
structures being substantially aligned along a first direction,
which may result in a substantially increased electrode surface
area as compared to flat substrates, which may further lead to
substantially higher charging rates of solid-state battery cells
comprising such three-dimensional electrode structure. In
embodiments of the sixth aspect of the present disclosure the
electrically conductive substrate may further comprise a plurality
of electrically conductive interconnecting structures oriented
along a second direction different from the first direction, such
as for example substantially orthogonal to the first direction,
wherein the electrically conductive interconnecting structures form
a connection between neighboring electrically conductive structures
oriented along the first direction.
[0065] Examples of spaced electrically conductive structures are
pillars, nanopillars, wires, nanowires, tubes (or "hollow" wires),
nanotubes, meshes, and nanomeshes. Such structures may enable the
formation of flexible battery cells, due to a reduced mechanical
stress upon bending.
[0066] In embodiments of the sixth aspect of the present disclosure
wherein the interlayer comprises a transition metal oxide,
depositing the interlayer may for example comprise
electrodeposition in a solution having a pH in the range of 7 to
12. The use of a neutral or basic solution for depositing the
interlayer on the substrate, e.g. transition metal substrate, may
allow for the formation of the interlayer with a reduced risk of
degradation of the substrate, e.g. transition metal substrate,
under the influence of the interlayer deposition process. Using an
electrodeposition process for depositing the interlayer may be
suitable for low-cost large-scale manufacturing. The transition
metal oxide may for example comprise chromium oxide, nickel oxide,
titanium oxide, or manganese oxide.
[0067] According to a seventh aspect, the present disclosure is
related to a method for fabricating a solid-state battery cell. A
method according to the seventh aspect of the present disclosure
comprises forming a plurality of spaced electrically conductive
structures on a substrate according to a method of the third aspect
of the present disclosure; forming a first layer of active
electrode material on the plurality of electrically conductive
structures, wherein the first layer of active electrode material
conformally coats surfaces of the plurality of electrically
conductive structures; depositing a solid electrolyte layer over
the first layer of active electrode material; and forming a second
layer of active electrode material over the solid electrolyte
layer, wherein one of the first layer of active electrode material
and the second layer of active electrode material forms a cathode
layer and the other one forms an anode layer of the solid-state
battery cell. The plurality of spaced electrically conductive
structures may form a first current collector of the solid-state
battery cell. The method may further comprise depositing a second
current collector or collector layer over the second layer of
active electrode material.
[0068] In embodiments of the method of the seventh aspect of the
present disclosure forming the first layer of active electrode
material on the plurality of electrically conductive structures may
be done according to an embodiment of the sixth aspect of the
present disclosure.
[0069] In general, features of the seventh aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0070] A method of the seventh aspect of the present disclosure may
include a substantial part of the fabrication steps being done by
using a straightforward, low-cost electrochemical deposition
process. More in particular, the anodization steps in the method
for forming a template, the step of depositing an electrically
conductive material within the template and the step of depositing
an electrode material precursor layer may be done using an
electrochemical deposition process. These steps may be done in the
same equipment. A method of the seventh aspect of the present
disclosure may include electrochemical deposition processes that
are performed in an aqueous solution without organic solvents,
resulting in an environmental-friendly fabrication method.
[0071] According to an eighth aspect, the present disclosure is
related to a method for fabricating a solid-state battery cell. A
method according to the eighth aspect of the present disclosure
comprises: forming a plurality of spaced electrically conductive
structures on a substrate; forming a first layer of active
electrode material on the plurality of spaced electrically
conductive structures in accordance with an embodiment of the sixth
aspect of the present disclosure, wherein the first layer of active
electrode material conformally coats surfaces of the plurality of
spaced electrically conductive structures; depositing a solid
electrolyte layer over the first layer of active electrode
material; and forming a second layer of active electrode material
over the solid electrolyte layer, wherein one of the first layer of
active electrode material and the second layer of active electrode
material forms a cathode layer and the other one forms an anode
layer of the solid-state battery cell. The plurality of spaced
electrically conductive structures may form a first current
collector layer of the solid-state battery cell. The method may
further comprise depositing a second current collector layer over
the second layer of active electrode material.
[0072] In general, features of the eighth aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0073] According to a ninth aspect, the present disclosure is
related to a method for fabricating a solid-state battery. A method
according to the ninth aspect of the present disclosure comprises:
fabricating a plurality of solid-state battery cells in accordance
with an embodiment of the seventh or the eighth aspect of the
present disclosure; and forming a stack of the plurality of
solid-state battery cells with a solid electrolyte being provided
in between neighboring solid-state battery cells.
[0074] In general, features of the ninth aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0075] According to a tenth aspect, the present disclosure is
related to a solid-state battery cell. A solid-state battery cell
according to the tenth aspect of the present disclosure comprises a
plurality of spaced electrically conductive structures; a first
layer of active electrode material conformally coating surfaces of
the plurality of spaced electrically conductive structures; a solid
electrolyte layer over the first layer of active electrode
material; a second layer of active electrode material over the
solid electrolyte layer, wherein one of the first layer of active
electrode material and the second layer of active electrode
material forms a cathode layer and the other one forms an anode
layer of the solid-state battery cell; and a 0.5 nm to 10 nm thick
interlayer between the plurality of electrically conductive
structures and the first layer of active electrode material,
wherein the interlayer comprises a transition metal oxide, a noble
metal, or a noble-metal oxide. In embodiments of the tenth aspect
of the present disclosure the plurality of spaced electrically
conductive structures may form a first current collector layer of
the solid-state battery cell. The solid-state battery cell may
further comprise a second current collector layer over the second
layer of active electrode material.
[0076] In general, features of the tenth aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0077] According to an eleventh aspect, the present disclosure is
related to a solid-date battery comprising at least one, for
example a plurality of, e.g. a stack of, solid-state battery cells
according to the tenth aspect of the present disclosure.
[0078] In general, features of the eleventh aspect of the present
disclosure provide similar features as discussed above in relation
to the previous aspects of the present disclosure.
[0079] Particular aspects of the disclosure are set out in the
accompanying independent and dependent claims. Features from the
dependent claims may be combined with features of the independent
claims and with features of other dependent claims as appropriate
and not merely as explicitly set out in the claims.
[0080] The above and other characteristics and features of the
present disclosure will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings,
which illustrate, by way of example, the principles of the
disclosure. This description is given for the sake of example only,
without limiting the scope of the disclosure. The reference figures
quoted below refer to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0081] FIG. 1 illustrates an example process sequence of a method
for transforming at least part of a valve metal layer into a
template comprising a plurality of spaced (nano)channels according
to an embodiment of the first aspect of the present disclosure.
[0082] FIG. 2 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 1.
[0083] FIG. 3 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 1.
[0084] FIG. 4 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 1.
[0085] FIG. 5 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 1.
[0086] FIG. 6 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 1.
[0087] FIG. 7 schematically shows a cross section of an example of
a template according to an embodiment of the second aspect of the
present disclosure.
[0088] FIG. 8 schematically shows a cross section of an example of
a template according to an embodiment of the second aspect of the
present disclosure.
[0089] FIG. 9 illustrates an example process sequence of a method
for forming a plurality of spaced (nano)structures on a substrate
according to an embodiment of the third aspect of the present
disclosure.
[0090] FIG. 10 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 9.
[0091] FIG. 11 schematically shows a cross section of an example of
an entity according to an embodiment of the fourth aspect of the
present disclosure.
[0092] FIG. 12A schematically shows a cross section of an example
of an entity according to an embodiment of the fourth aspect of the
present disclosure.
[0093] FIG. 12B schematically shows a cross section of an example
of an entity according to an embodiment of the fourth aspect of the
present disclosure.
[0094] FIG. 13 illustrates an example process sequence of a method
for forming a layer of functional material on an electrically
conductive substrate according to an embodiment of the sixth aspect
of the present disclosure.
[0095] FIG. 14 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 13.
[0096] FIG. 15 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 13.
[0097] FIG. 16 schematically shows a cross section illustrating
results of a step of the process sequence of FIG. 13.
[0098] FIG. 17 shows potential transients as measured during
galvanostatic deposition of a MnO.sub.x cathode precursor layer on
Ni nano-mesh samples. The curves labeled (a) corresponds to samples
without an interlayer being provided, whereas the curve labeled (b)
corresponds to samples covered with an interlayer in accordance
with an embodiment of the third aspect of the present
disclosure.
[0099] FIG. 18 shows results of a cyclic voltammetry experiment on
a structure comprising a nickel substrate with a MnO.sub.x layer
deposited thereon. Curves labeled (a) correspond to a structure
without an interlayer being provided, whereas curves labeled (b)
correspond to a structure having an interlayer provided thereon
before deposition of the MnO.sub.x layer, in accordance with an
embodiment of the third aspect of the present disclosure.
[0100] FIG. 19 schematically shows a cross section of an example of
a solid-state battery cell according to an embodiment of the tenth
aspect of the present disclosure.
[0101] FIG. 20 schematically shows a cross section of an example of
a solid-state battery according to an embodiment of the eleventh
aspect of the present disclosure.
[0102] FIG. 21A shows an Scanning Electron Microscopy (SEM) image
of a sample wherein MnO.sub.x is electrodeposited on a Ni nano-mesh
substrate with a NiO interlayer.
[0103] FIG. 21B shows an SEM image of a sample wherein MnO.sub.x is
electrodeposited on a Ni nano-mesh substrate without an
interlayer.
[0104] FIG. 21C shows an SEM image of a sample wherein MnO.sub.x is
electrodeposited on a Ni nano-mesh substrate according to
embodiments of the sixth aspect of the present disclosure. In the
different figures, the same reference signs refer to the same or
analogous elements.
DETAILED DESCRIPTION
[0105] The present disclosure will be described with respect to
particular embodiments and with reference to certain drawings but
the disclosure is not limited thereto but only by the claims. The
drawings described are only schematic and are non-limiting. In the
drawings, the size of some of the elements may be exaggerated and
not drawn on scale for illustrative purposes. The dimensions and
the relative dimensions do not correspond to actual reductions to
practice of the disclosure.
[0106] The terms first, second, third,. and the like in the
description and in the claims, are used for distinguishing between
similar elements and not necessarily for describing a sequence,
either temporally, spatially, in ranking or in any other manner. It
is to be understood that the terms so used are interchangeable
under appropriate circumstances and that the embodiments of the
disclosure described herein are capable of operation in other
sequences than described or illustrated herein.
[0107] It is to be noticed that the term "comprising", used in the
claims, should not be interpreted as being restricted to the means
listed thereafter; it does not exclude other elements or steps. It
is thus to be interpreted as specifying the presence of the stated
features, integers, steps or components as referred to, but does
not preclude the presence or addition of one or more other
features, integers, steps,. or components, or groups thereof. Thus,
the scope of the expression "a device comprising A and B" should
not be limited to devices consisting only of components A and B. It
means that with respect to the present disclosure, the only
relevant components of the device are A and B.
[0108] Reference throughout this specification to "one embodiment"
or "an embodiment" means that a particular feature, structure or
characteristic described in connection with the embodiment is
included in at least one embodiment of the present disclosure.
Thus, appearances of the phrases "in one embodiment" or "in an
embodiment" in various places throughout this specification are not
necessarily all referring to the same embodiment, but may.
Furthermore, the particular features, structures or characteristics
may be combined in any suitable manner, as would be apparent to one
of ordinary skill in the art from this disclosure, in one or more
embodiments.
[0109] Similarly it should be appreciated that in the description
of example embodiments of the disclosure, various features of the
disclosure are sometimes grouped together in a single embodiment,
figure, or description thereof for the purpose of streamlining the
disclosure and aiding in the understanding of one or more of the
various inventive aspects. This method of disclosure, however, is
not to be interpreted as reflecting an intention that the claimed
disclosure requires more features than are expressly recited in
each claim. Rather, as the following claims reflect, inventive
aspects lie in less than all features of a single foregoing
disclosed embodiment. Thus, the claims following the detailed
description are hereby expressly incorporated into this detailed
description, with each claim standing on its own as a separate
embodiment of this disclosure.
[0110] Furthermore, while some embodiments described herein include
some but not other features included in other embodiments,
combinations of features of different embodiments are meant to be
within the scope of the disclosure, and form different embodiments,
as would be understood by those in the art. For example, in the
following claims, any of the claimed embodiments can be used in any
combination.
[0111] In the description provided herein, numerous specific
details are set forth. However, it is understood that embodiments
of the disclosure may be practiced without these specific details.
In other instances, standardized methods, structures, and
techniques have not been shown in detail in order not to obscure an
understanding of this description.
[0112] The following terms are provided solely to aid in the
understanding of the disclosure.
[0113] In the context of the present disclosure, a battery cell is
a structure comprising two electrode layers with an electrolyte
layer in between, i.e. a structure comprising a stack of a first
electrode layer (first layer of active electrode
material)/electrolyte layer/second electrode layer (second layer of
active electrode material). The first electrode layer and the
second electrode layer are of opposite polarity. A battery may
comprise a single battery cell or it may comprise a plurality of,
e.g. at least two, battery cells. A battery may comprise two or
more battery cells connected in series or in parallel, or a
combination of series and parallel connected battery cells. A
battery further comprises a first current collector layer and a
second collector layer, the first current collector layer and the
second current collector layer being of opposite polarity.
[0114] In the context of the present disclosure, an ion insertion
battery cell is a battery cell comprising electrodes that can
accept or release cations or anions during operation of the battery
cell. Ion insertion battery cells can rely on the
insertion/extraction of only one cation element, multiple cation
elements, only anions or a mixture of anion and cation elements. An
ion insertion battery cell further comprises an electrolyte that
allows for ionic conduction of the respective ion used, while being
(electro)chemically stable with regard to the used electrode
materials.
[0115] In a rechargeable battery cell, each of the electrodes has a
first polarity during the discharge (i.e. battery operation) and a
second, opposite polarity during charging. Technically speaking
however, the negative electrode is the anode during the discharge
and the cathode during charging. Vice versa, the positive electrode
is the cathode during discharge and the anode when charging the
battery. In the context of the present disclosure, the terminology
of the discharge (i.e. battery operation) is used. Herein further,
with anode the negative electrode is meant and with cathode the
positive electrode is meant. Through the disclosure, when referred
to "anode material" it is meant the negative electrode material and
when referred to "cathode material" it is meant the positive
electrode material.
[0116] In the context of the present disclosure, an active
electrode material is a material that is a component of a battery
electrode layer. In the active electrode material, the actual
electrochemical transformation (change in valence or oxidation
state of the atoms) takes place, which gives rise to storage of
chemical energy in the electrode. An electrode layer is typically
composed of the active electrode material and supporting
material.
[0117] In the context of the present disclosure, the term
"anodization" when applied to a valve metal (such as for example
aluminum) or to a valve metal layer refers to an electrochemical
process comprising applying a potential or a current between the
valve metal layer (the material to be anodized) functioning as a
working electrode at one hand and a counter-electrode at the other
hand, in the presence of an acid electrolyte. This method leads to
the formation of a porous layer of valve metal oxide comprising
plurality of pores or channels, e.g. a cluster of channels,
arranged in an orderly fashion (e.g. hexagonally) perpendicularly
to the surface of the layer. This cluster may be referred to as an
array, due to the orderly nature of the arrangement.
[0118] In the context of the present disclosure, a valve metal is a
metal that can be oxidized using an anodization process (anodic
oxidation) to thereby form a stable valve metal oxide. More in
particular, in the context of the present disclosure, a valve metal
is a metal selected from the group of aluminum, tungsten, titanium,
tantalum, hafnium, niobium, vanadium, and zirconium. In the context
of the present disclosure, a valve metal layer is a layer
comprising a valve metal or a valve metal alloy (or a "doped" valve
metal). An example of an aluminum alloy that may for example be
used in the context of the present disclosure is a copper doped
aluminum layer, e.g. with a doping concentration in the range
between 1% and 10%, the present disclosure not being limited
thereto.
[0119] In the context of the present disclosure, when referring to
a substrate, the substrate may be a planar substrate or a
non-planar, e.g. three-dimensional (3D) substrate. In the context
of the present disclosure, a 3D substrate may for example comprise
a plurality of 3D features, 3D structures, such as 3D micro- or
nano-structures, such as for example a plurality of micro-pillars
or nano-pillars, a plurality of microwires or nanowires or 3D
(nano)meshes, (nano)tubes, and/or other porous structures, such as
for example porous anodized alumina. The 3D features may be present
in a regular pattern, such as for example a regular array pattern,
or they may be randomly distributed over the substrate.
[0120] In the context of the present disclosure, a plurality of
spaced channels refers to a plurality of channels that are
separated in space from one another, i.e. that are located at a
distance from each other. The plurality of spaced channels may be
either completely separated from each other, e.g. by a surrounding
medium, or they may be interconnected, for example partially
interconnected, e.g. by a plurality of interconnecting channels
through a surrounding medium. The plurality of interconnecting
channels may for example have a longitudinal orientation
substantially orthogonal to a longitudinal orientation of the
plurality of spaced channels.
[0121] In the context of the present disclosure, a template
comprising a plurality of spaced channels aligned longitudinally
along a direction may refer to a template comprising a plurality of
channels being completely separated from each other or to a
template comprising a plurality of channels that are
interconnected, for example partially interconnected by a plurality
of interconnecting channels. The interconnecting channels may be
oriented in a direction substantially orthogonal to the
longitudinal direction of the plurality of spaced channels. In the
context of the present disclosure, a template comprising a
plurality of spaced channels aligned longitudinally along a
direction may refer to a template comprising two or more regions
positioned subsequently along the longitudinal direction, wherein
at least a first region comprises a plurality of completely
separated (non-interconnected) spaced channels and wherein at least
a second region comprises a plurality of interconnected spaced
channels (being interconnected by interconnecting channels).
[0122] In the context of the present disclosure, a plurality of
spaced structures, e.g. nanostructures, aligned longitudinally
along a direction refers to a plurality of structures, e.g.
nanostructures, that are located at a distance from each other. The
plurality of (nano)structures may for example comprise
(nano)pillars, (nano)wires, (nano)meshes, or (nano)tubes. The
plurality of structures, e.g. nanostructures, may be either
completely separated from each other, e.g. by a surrounding medium
such as air or a solid material different from the (nano)structure
material, or they may be interconnected, for example partially
interconnected, e.g. by a plurality of interconnecting structures,
e.g. interconnecting nanostructures. The plurality of
interconnecting (nano)structures may for example have a
longitudinal orientation substantially orthogonal to a longitudinal
orientation of the plurality of spaced (nano)structures. The
interconnecting (nano)structures are typically made of the same
material as the spaced (nano)structures themselves. In the context
of the present disclosure, a plurality of spaced (nano)structures
aligned longitudinally along a direction may refer to structure
comprising two or more regions positioned subsequently along the
longitudinal direction, wherein at least a first region comprises a
plurality of spaced, completely separated (non-interconnected)
(nano)structures and wherein at least a second region comprises a
plurality of spaced, interconnected (nano)structures (for example
being interconnected by interconnecting (nano)structures).
[0123] In the context of the present disclosure, a functional
material or functional material layer is a material or material
layer that satisfies or provides a defined functionality and/or has
defined properties, adjusted for a device in which it is
integrated. A functional material may for example comprise a metal,
a metal alloy, a semiconductor, an oxide, a metal hydride, a
ceramic material, a metal-organic crystal, a polymer, or an organic
supramolecular solid, the present disclosure not being limited
thereto. It provides a defined functionality or property, such as
for example a high electrical conductivity, catalytic activity
towards chemical reactions, electrochemical activity towards ion
insertion, high optical absorbance, iridescence, photoluminescence,
high magnetic anisotropy, or piezoelectricity, the present
disclosure not being limited thereto. This is adjusted for the
final device or intended field of application in which it is used.
A functional material or a functional material layer may for
example have the functionality of an electrode, a current
collector, a catalyst, an energy storage material, a light
absorber, a photonic crystal, a light emitter, an information
storage medium, an ion trap, or a gas absorber, the present
disclosure not being limited thereto.
[0124] The disclosure will now be described by a detailed
description of several embodiments of the disclosure. It is clear
that other embodiments of the disclosure can be configured
according to the knowledge of persons skilled in the art without
departing from the technical teaching of the disclosure, the
disclosure being limited only by the terms of the appended
claims.
[0125] According to a first aspect, the present disclosure is
related to a method for transforming at least part of a valve metal
layer into a template comprising a plurality of spaced
(nano)channels aligned longitudinally along a first direction. An
example of a method according to an embodiment of the first aspect
of the present disclosure is schematically illustrated in FIG. 1,
showing a flow chart comprising an example process sequence and in
FIG. 2 to FIG. 8, schematically showing cross sections illustrating
results of successive steps of the process sequence of FIG. 1.
[0126] As illustrated in the example shown in FIG. 1, a method 100
according to an embodiment of the first aspect of the present
disclosure comprises a first anodization step 101 of at least part
of a valve metal layer, the first anodization step 101 resulting in
the formation of a porous layer of valve metal oxide comprising a
plurality of aligned spaced (nano)channels having bottom surfaces
coated with a first insulating metal oxide barrier. The plurality
of (nano)channels formed as a result of the first anodization step
are substantially aligned longitudinally along a first direction.
The plurality of (nano)channels each have (nano)channel walls
substantially aligned longitudinally along the first direction and
a (nano)channel bottom substantially parallel with a surface of the
valve metal layer. As a result of the first anodization step the
surfaces of the (nano)channel bottoms are covered with a first
insulating metal oxide barrier layer, for example a first valve
metal oxide barrier layer.
[0127] In embodiments of the first aspect of the present disclosure
the valve metal layer may be a free-standing layer, for example a
flexible free-standing layer such as a metal foil, or the valve
metal layer may be provided on a substrate, for example on a rigid
substrate or on a flexible substrate. FIG. 2 illustrates an example
of an embodiment wherein the valve metal layer 11 is a
free-standing layer, but the present disclosure is not limited
thereto. The first anodization step 101 may result in a structure
as schematically shown in FIG. 3. It illustrates formation of a
porous layer 12 of anodized metal comprising a plurality of spaced
(nano)channels 13 that are substantially aligned longitudinally
along a first direction. In embodiments of the present disclosure
the first direction may correspond to a thickness direction of the
valve metal layer, i.e. it may be substantially orthogonal to a
surface of the valve metal layer, as schematically illustrated in
the example shown in FIG. 3. However, the present disclosure is not
limited thereto, and the first direction may be at an angle, for
example at an angle in the range between 60.degree. and 90.degree.,
with respect to a surface of the valve metal layer. FIG. 3
illustrates an example wherein the first direction is orthogonal to
the surface of the valve metal layer 11. In other words, the first
direction corresponds to a thickness direction Y of the valve metal
layer 11. The plurality of (nano)channels 13 each have
(nano)channel walls 14 substantially aligned longitudinally along
the thickness direction Y and a (nano)channel bottom 15. As a
result of the first anodization step 101 the surface of the
(nano)channel bottoms 15 is covered with a first insulating metal
oxide barrier layer 21, as shown more in detail in the inset of
FIG. 3.
[0128] In the example illustrated in FIG. 3 the porous layer 12
comprising the plurality of channels 13 is formed only in a part of
the valve metal layer. However, the present disclosure is not
limited thereto. For example, in embodiments according to the first
aspect wherein the valve metal layer 11 is provided on a substrate
(not illustrated) the porous layer 12 comprising the plurality of
(nano)channels 13 may also be formed throughout the valve metal
layer 11, thereby exposing the underlying substrate at the channel
bottoms.
[0129] In embodiments of the present disclosure (not illustrated)
the first anodization step may comprise complete immersion of a
free-standing valve metal layer 11 in an anodizing solution. In
such embodiments, the first anodization step may result in the
formation of a first porous layer of valve metal oxide comprising a
plurality of spaced (nano)channels at a first side of the valve
metal layer and simultaneously in the formation of a second porous
layer of valve metal oxide comprising a plurality of spaced
(nano)channels at a second, opposite side of the valve metal layer.
In between the first porous layer and the second porous layer a
non-anodized valve metal layer remains.
[0130] A method 100 according to embodiments of the first aspect of
the present disclosure comprises, after the first anodization step
101, performing a protective treatment 102 (FIG. 1). The protective
treatment induces hydrophobic surfaces to the (nano)channel walls
14 and (nano)channel bottoms 15, i.e. it results in (nano)channels
13 having hydrophobic (nano)channel wall surfaces and hydrophobic
(nano)channel bottom surfaces.
[0131] In embodiments of the first aspect of the present
disclosure, performing the protective treatment may comprise
annealing 102, 1021 (FIG. 1), such as for example annealing at a
temperature in the range between 300.degree. C. and 550.degree. C.
The annealing may be done in an inert atmosphere, such as for
example in nitrogen or argon, or in air. Annealing may be done
under ambient pressure or at a reduced pressure, such as in
vacuum.
[0132] In embodiments of the first aspect of the present
disclosure, performing the protective treatment may comprise
depositing 102, 1022 (FIG. 1) a protective layer over the
(nano)channel walls and over the (nano)channel bottoms. This is
schematically illustrated in FIG. 4, showing a protective layer 31
being provided on the (nano)channel walls 14 and on the first
insulating metal oxide barrier layer 21 that is present on the
(nano)channel bottoms 15. The protective layer 31 is also formed on
an upper surface of the porous layer 12.
[0133] In embodiments the protective layer may be a layer
comprising hydrophobic silane, e.g. formed by vapor deposition, for
example in air or in vacuum, for example at a temperature in the
range between 80.degree. C. and 120.degree. C. In other embodiments
the protective layer may be a polymer layer, e.g. formed by
application of polymer solution onto the pore walls and bottoms of
the template and drying. Such a protective polymer layer may for
example be formed by immersing the sample in 1% to 20% solution of
polystyrene or PMMA (poly(methyl 2-methylpropanoate)) or PDMS
(poly(dimethylsiloxane)), dissolved in acetone, in toluene or in a
chlorinated solvent such as dichloromethane and spin coating the
excess of the solution, followed by drying at a temperature e.g. in
the range between 20.degree. C. and 60.degree. C., e.g. in air or
in vacuum.
[0134] In embodiments of the first aspect of the present
disclosure, performing the protective treatment may comprise both
depositing 102, 1022 (FIG. 1) a protective layer 31 over, e.g.
directly on, the (nano)channel walls and over the (nano)channel
bottoms and annealing 102, 1021 (FIG. 1).
[0135] The protective treatment results in the formation of
hydrophobic surfaces on the (nano)channel walls and (nano)channel
bottoms. Such a hydrophobic surface may provide protection against
wetting, e.g. against wetting by an etchant used in subsequent
process steps, and therefore it may provide protection against
etching.
[0136] A method 100 according to embodiments of the first aspect of
the present disclosure comprises, after the protective treatment
102, 1021, 1022, a second anodization step 103 (FIG. 1). The second
anodization step may for example be done using similar anodization
conditions as used for the first anodization step (e.g., for a
relatively short period, such as for example 1 minute to 30
minutes). In embodiments of the first aspect of the present
disclosure, this second anodization step affects the (nano)channel
bottoms only and induces hydrophilic surfaces at the (nano)channel
bottoms only. In embodiments wherein a protective layer 31 has been
deposited (FIG. 1, step 1022; FIG. 4), the second anodization step
103 results in removal of the protective layer 31 from the bottom
of the plurality of spaced (nano)channels. The second anodization
step thus results in the formation of hydrophilic, unprotected
(nano)channel bottoms (e.g. not protected against wetting). The
second anodization step further results in removal of the first
insulating metal oxide barrier layer 21 from the (nano)channel
bottoms. The second anodization step leaves the plurality of
(nano)channel walls substantially unaffected, i.e. the plurality of
(nano)channel walls remain substantially protected. The second
anodization step results in further anodization only at the bottoms
of the plurality of (nano)channels and creates a second
(unprotected) insulating metal oxide barrier layer at the
(nano)channel bottoms.
[0137] FIG. 5 schematically illustrates a cross section of the
structure as may be obtained after having performed the second
anodization step in a method according to an embodiment of the
first aspect of the present disclosure wherein the protective
treatment comprises annealing. More in particular, FIG. 5
illustrates the first metal oxide barrier layer 21 being removed
from the channel bottoms 15 and being replaced by a second metal
oxide barrier layer 22 at the channel bottoms 15 as a result of the
second anodization step 103.
[0138] FIG. 6 schematically illustrates a cross section of the
structure as may be obtained after having performed the second
anodization step in a method according to an embodiment of the
first aspect of the present disclosure wherein the protective
treatment comprises depositing a protective layer 31. More in
particular, FIG. 6 illustrates the protective layer 31 and the
first metal oxide barrier layer 21 being removed from the channel
bottoms 15 and being replaced by a second metal oxide barrier layer
22 at the channel bottoms 15 as a result of the second anodization
step 103. FIG. 6 further illustrates that the channel walls 14
remain protected by protective layer 31.
[0139] A method 100 according to embodiments of the first aspect of
the present disclosure further comprises an etching step 104 (FIG.
1), for example in an acidic etching solution or in a basic etching
solution. At this stage of the process the (nano)channel walls 14
are substantially protected against etching, e.g. against wetting,
as a result of the protective treatment 102 previously performed,
resulting in hydrophobic surfaces at the (nano)channel walls. At
this stage of the process only the (nano)channel bottoms 15 (more
in particular the second insulating metal oxide barrier layer 22 at
the (nano)channel bottoms 15) are subject to wetting and thus
etching. Therefore, this etching step 104 only removes the second
insulating metal oxide barrier layer 22 from the plurality of
(nano)channel bottoms 15 and does not affect the porous layer 12.
As such, a widening of the plurality of (nano)channels 13 during
this etching step may be substantially avoided. The etching step
may for example comprise etching in an aqueous solution of
H.sub.3PO.sub.4 or KOH. The etching solution may comprise a surface
tension adjusting agent such as for example ethanol, isopropyl
alcohol, acetone or sodium dodecyl sulfate, the present disclosure
not being limited thereto. For example, a solution comprising 1 wt
% to 30 wt % of H.sub.3PO4 and 1 wt % to 60 wt % of isopropyl
alcohol in water may be used for the etching step.
[0140] FIG. 7 schematically illustrates a cross section of the
structure as may be obtained after having performed the etching
step 104 in a method 100 according to an embodiment of the first
aspect of the present disclosure wherein the protective treatment
comprises annealing. More in particular, FIG. 7 illustrates that,
after this etching step 104, the (nano)channel bottoms 15 are
exposed (i.e. the second metal oxide barrier layer 22 has been
removed from the (nano)channel bottoms 15). The (nano)channel walls
14 remain unaffected, and there is no widening of the
(nano)channels 13.
[0141] FIG. 8 schematically illustrates a cross section of the
structure as may be obtained after having performed the etching
step 104 in a method 100 according to an embodiment of the first
aspect of the present disclosure wherein the protective treatment
comprises depositing a protective layer. More in particular, FIG. 8
illustrates that, after this etching step 104, the (nano)channel
bottoms 15 are exposed (i.e. the second metal oxide barrier layer
22 has been removed from the (nano)channel bottoms 15). It also
illustrates that the (nano)channel walls 14 are still covered with
the protective layer 31.
[0142] As illustrated in FIG. 7 and in FIG. 8, the structure
obtained after performing the etching step comprises a template 20
comprising a plurality of spaced (nano)channels 13 aligned
longitudinally along a first direction (in the example shown the
thickness direction Y of the valve metal layer) and a substrate 10
supporting the template 20. FIG. 7 and FIG. 8 thus illustrate
examples of a template 20 according to embodiments of the second
aspect of the present disclosure. In the examples shown in FIG. 7
and FIG. 8 the substrate 10 corresponds to a remaining,
non-anodized part of the valve metal layer 11.
[0143] After the etching step 104 the structure comprising the
substrate 10 and the template 20 (FIG. 7, FIG. 8) may be immersed
in a basic solution of zinc oxide to thereby produce a thin
conductive zinc layer at the (nano)channel bottoms. The presence of
such a thin conductive zinc layer at the (nano)channel bottoms
enables or facilitates electroplating of a variety of metals in the
plurality of (nano)channels in a subsequent step.
[0144] In embodiments of the present disclosure the valve metal
layer 11 may consist of a single layer or it may comprise more than
one, e.g. a plurality of (stacked) layers, e.g. having a different
composition. For example, the valve metal layer may consist of an
aluminum layer, such as for example an aluminum layer of 99% or
higher purity, with a thickness for example in the range between 1
micrometer and 1 mm. In other embodiments it may for example
consist of a doped aluminum layer, such as for example a copper
doped aluminum layer, e.g. with a doping concentration in the range
between 1% and 10% and a thickness e.g. in the range between 1
micrometer and 1 mm. In other embodiments, it may be a layer stack
comprising a first layer and a second layer, wherein the first
layer is for example an aluminum layer of 99% or higher purity and
wherein the second layer is for example a doped, e.g. copper doped,
aluminum layer. The doped aluminum layer may for example have a
doping concentration in the range between 1% and 10% and the
thickness of this layer may for example be in the range between 1
micrometer and 100 micrometers.
[0145] In embodiments of the present disclosure the valve metal
layer 11 may be a free-standing layer such as a free-standing foil,
such as for example an aluminum foil, e.g. having a thickness in
the range between 10 micrometers and 1 millimeter. In other
embodiments of the present disclosure, the layer valve metal layer
may be a non-free-standing layer: it may for example be provided on
a substrate, such as a flexible substrate. Using a flexible
substrate may allow for the fabrication of flexible solid-state
batteries. Examples of flexible substrates that may be used are a
metal foil (such as aluminum, nickel, or copper foil), mica and
polyimide tape. The substrate may be coated with an electrically
conductive layer such as a nickel layer, a titanium layer, or a
titanium nitride layer.
[0146] In embodiments wherein the valve metal layer is a
free-standing layer, the first anodization step may only be done in
part of the layer, i.e. not throughout the valve metal layer, such
that a part of the layer remains unaffected. In such embodiments
the remaining (non-anodized) part of the valve metal layer can be
maintained as a carrier (or substrate 10) for the anodized part
(template 20). In the further description, when reference is made
to a substrate, this may refer to a substrate on which a valve
metal layer is initially provided, or, in embodiments wherein a
free-standing valve metal layer is used, it may refer to a
substrate 10 corresponding to a part of the valve metal layer that
is remaining after the anodization step (i.e. the part that is not
anodized, not transformed into a porous layer), as for example
illustrated in FIG. 7 and FIG. 8. In embodiments wherein the
anodization steps comprise complete immersion of a free standing
valve metal layer 11 in an anodizing solution, resulting in the
formation of a first porous layer of valve metal oxide at a first
side of the valve metal layer and simultaneously in the formation
of a second porous layer of valve metal oxide at a second, opposite
side of the valve metal layer, the substrate 10 (non-anodized part)
is present between the first porous layer and the second porous
layer. In other words, a "first porous layer/substrate/second
porous layer" stack is formed.
[0147] The first anodization step of the valve metal layer, for
example a layer comprising aluminum, may be performed by immersing
the valve metal layer al in an anodizing solution, for example an
acidic medium, such as a solution of sulfuric, oxalic, or
phosphoric acid and applying a constant voltage difference between
the valve metal layer and a counter electrode such as a titanium
electrode (e.g. a sheet or a mesh) or a platinum electrode
(potentiostatic anodization). The voltage difference may for
example be in the range between 10 V and 500 V. Alternatively, a
constant current may be applied to the valve metal layer through
the anodizing solution (galvanostatic anodization). By selecting
and controlling the anodization parameters the size of the
plurality of (nano)channels (e.g. their diameter), and the
distribution of the plurality of (nano)channels (e.g. the distance
between neighboring (nano)channels) may be well controlled.
[0148] For example, experiments were performed wherein a potential
of 40 V was applied between an aluminum layer (working electrode)
and a counter electrode, in a 0.3M oxalic acid at 30.degree. C. to
perform anodization of an aluminum layer. This resulted in the
formation of a plurality of 40 nm wide (i.e. having a diameter of
40 nm) spaced nanochannels having a longitudinal direction
substantially orthogonal to the aluminum layer surface, the
plurality of nanochannels being located at a distance from each
other (distance between the centers of the nanochannels) of about
100 nm in a direction substantially parallel with the aluminum
layer surface.
[0149] The longitudinal size of the plurality of spaced
nanochannels (i.e. the length of the nanochannels, corresponding to
the depth of anodization into the valve metal layer, i.e. the
distance between the nanochannel bottoms and an upper surface of
the valve metal layer) depends on the duration of the first
anodization step. It may for example be in the range between 100 nm
and 100 micrometers, the present disclosure not being limited
thereto. The first anodization step may for example have a duration
in the range between 1 hour and 12 hours.
[0150] Where the valve metal layer comprises an aluminum layer of
high purity, such as for example an aluminum layer of 99% or higher
purity, the first anodization step results in the formation of a
plurality of separated, non-interconnected (nano)channels. Where
the valve metal layer comprises a doped aluminum layer, such as for
example a copper doped aluminum layer, e.g. with a doping
concentration in the range between 1% and 10%, the first
anodization step results in the formation of a plurality of spaced
(nano)channels that are interconnected by interconnecting
(nano)channels having a longitudinal orientation substantially
orthogonal to the longitudinal orientation of the plurality of
spaced (nano)channels. In embodiments wherein the valve metal layer
is a layer stack comprising a first layer and a second layer,
wherein the first layer is for example an aluminum layer of 99% or
higher purity and wherein the second layer is a doped, e.g. copper
doped, aluminum layer, a plurality of spaced (nano)channels is
formed wherein the plurality of spaced (nano)channels are separated
(non-interconnected) in a first region (corresponding to the first
layer) and wherein the plurality of spaced (nano)channels are
interconnected in a second region (corresponding to the second
layer). The formation of interconnecting (nano)channels may result
in an increased surface area and an improved mechanical stability
of (nano)structures that may be formed subsequently within the
template.
[0151] For example, experiments were performed wherein a potential
of 40 V was applied between a Cu doped aluminum layer (working
electrode) and a counter electrode, in a 0.3M oxalic acid at
30.degree. C. This resulted in the formation of a plurality of 40
nm wide spaced nanochannels having a longitudinal direction
substantially orthogonal to the metal layer surface, the plurality
of spaced nanochannels being located at a distance from each other
of about 100 nm in a direction substantially parallel with the
metal layer surface, and in addition to the formation of 40 nm wide
branches or interconnecting nanochannels having a longitudinal
direction substantially parallel to the metal layer surface and
being separated by a distance of about 100 nm in a direction
substantially orthogonal to the metal layer surface.
[0152] In embodiments wherein the valve metal layer is provided on
a substrate, such as a flexible substrate, coated with an
electrically conductive layer such as for example a nickel,
titanium, or titanium nitride layer, the first anodization step may
proceed till a plurality of (nano)channels if formed throughout the
valve metal layer. In such embodiments, the bottom of the plurality
of (nano)channels thus formed is located at an interface between
the valve metal layer and the underlying electrically conductive
layer, i.e. at an interface between the porous layer resulting from
the first anodization step and the substrate 10. When during the
first anodization step the bottom of the plurality of
(nano)channels reaches the underlying substrate 10, this leads to a
decrease of current in case of potentiostatic anodization, or an
increase in potential in case of galvanostatic anodization. In this
way, it may be easily detected when the spaced (nano)channels 13
thus formed reach the substrate 10, i.e. at which moment the
plurality of spaced (nano)channels are formed throughout the valve
metal layer.
[0153] In embodiments, the second anodization step 103 may be
performed under irradiation of ultrasonic waves. Such ultrasonic
waves may for example be generated by a ultrasound generating horn,
immersed in the anodizing solution. Providing ultrasonic waves may
facilitate removal of the first insulating metal oxide barrier
layer 21 and, if present, removal of the protective layer 31 from
the (nano)channel bottoms during the second anodization step 103.
Providing ultrasonic waves may further facilitate removal of the
second insulating metal oxide barrier layer 22 from the
(nano)channel bottoms during the etching step 104.
[0154] According to a third aspect, the present disclosure is
related to a method for forming a plurality of spaced
(nano)structures, such as for example a plurality of spaced
electrically conductive (nano)structures, on a substrate. An
example of a method according to the third aspect of the present
disclosure is schematically illustrated in FIG. 9, showing a flow
chart comprising an example process sequence, and in FIG. 7, FIG.
8, FIG. 10 and FIG. 11, schematically showing cross sections
illustrating results of successive steps of the process sequence of
FIG. 9.
[0155] As illustrated in the example shown in FIG. 9, a method 200
according to an embodiment of the third aspect of the present
disclosure comprises first transforming 201 at least part of a
valve metal layer 11 into a template 20 comprising a plurality of
spaced (nano)channels 13 aligned longitudinally along a first
direction, in accordance with a method 100 of the first aspect of
the present disclosure. Examples of a structure resulting from this
step 201 are schematically shown in FIG. 7 and FIG. 8.
[0156] The method 200 further comprises depositing 202 a solid
functional material within the (nano)channels 13 of the template
20. This results in formation of a plurality of spaced
(nano)structures 40 inside the plurality of spaced channels 13, the
plurality of spaced (nano)structures being aligned longitudinally
along the first direction, as schematically shown in FIG. 10. In
the example shown in FIG. 10, the plurality of (nano)channels 13 is
completely filled with the solid functional material, resulting in
a plurality of (nano)wires 40 having a length (size in their
longitudinal direction Y) substantially equal to a thickness of the
template 20. However, the present disclosure is not limited thereto
and in embodiments of the second aspect of the present disclosure
the plurality of (nano)channels 13 may be filled only partially.
For example, in embodiments the functional material may be
deposited within the plurality of (nano)channels 13 only in part of
longitudinal direction Y, resulting in a plurality of
(nano)structures 40 having a length smaller than a thickness of
template 20. This can be controlled by controlling the deposition
time.
[0157] In embodiments of a method of the third aspect of the
present disclosure the solid functional material may be deposited
within the plurality of (nano)channels 13 to thereby fully fill the
plurality of (nano)channels 13 in lateral direction X, which may
result for example in the formation of a plurality of (nano)wires
or (nano)pillars within the plurality of (nano)channels. In other
embodiments, the solid functional material may be deposited within
the plurality of (nano)channels 13 to thereby only partially fill
the plurality of (nano)channels 13 in lateral direction X, which
may for example result in the formation of a plurality of
(nano)tubes or hollow (nano)wires inside the plurality of
(nano)channels 13.
[0158] After having deposited the solid functional material, the
template 20 may be removed by etching 203 (FIG. 9). For this
etching step 203, for example a solution comprising 0.1M to 1M KOH
may be used. The etching time may for example be in the range
between 20 minutes and 90 minutes, and etching may be done at a
temperature e.g. in the range between 20.degree. C. and 60.degree.
C. The resulting structure is schematically shown in FIG. 11. It
contains a plurality of spaced (nano)structures 40 on a substrate
10, more in particular on an electrically conductive substrate 10.
The diameter of the plurality of (nano)structures 40, i.e. their
size in lateral direction X, and their separation (i.e. the
center-to-center distance between neighboring (nano)structures 40)
depends on the diameter and separation of the (nano)channels 13 of
the template 20. The diameter of the plurality of (nano)wires may
for example be in the range between 10 nm and 500 nm, for example
between 10 nm and 300 nm, e.g. between 15 nm and 200 nm or between
50 nm and 200 nm, and their separation distance may for example be
in the range between 15 nm and 500 nm, e.g. between 50 nm and 250
nm, the present disclosure not being limited thereto.
[0159] In embodiments wherein the template is formed by anodization
of only a part of the valve metal layer 11 (i.e. wherein
anodization is done only partially in the thickness direction Y of
the valve metal layer 11), such as in embodiments using a
free-standing valve metal layer, the non-anodized part of the valve
metal layer remains as a carrier or substrate 10 for the plurality
of spaced (nano)structures 40 formed within the template. In such
embodiments removal of the template 20 results in a plurality of
spaced (nano)structures 40 on a remaining part of the valve metal
layer (herein also referred to as a substrate 10), wherein the
plurality of spaced (nano)structures 40 is substantially aligned
longitudinally with their longitudinal direction along the first
direction, such as for example a direction Y substantially
orthogonal to the valve metal layer (substrate) surface, i.e.
substantially orthogonal to direction X
[0160] In embodiments of the third aspect of the present
disclosure, depositing the solid functional material may comprise
depositing an electrically conductive material, a semiconductor
material, an electrically insulating material, or a combination
thereof. Depositing the solid functional material may for example
comprise Chemical Vapor Deposition, e.g. Atomic Layer Deposition,
the present disclosure not being limited thereto. Depositing an
electrically conductive material may for example comprise
depositing the material by galvanostatic or potentiostatic
electrodeposition or plating, the present disclosure not being
limited thereto.
[0161] For example, in a method 200 according to embodiments of the
third aspect of the present disclosure, nickel (nano)structures 40
may be grown galvanostatically from a solution of nickel sulphamate
and boric acid and/or nickel chloride at a temperature in the range
between 20.degree. C. and 60.degree. C. The growth may be performed
by application of a cathodic current e.g. (1-20 mA/cm.sup.2)
between the electrically conductive substrate 10 (or an
electrically conductive layer being part of the substrate 10) and a
metallic counter electrode, such as a nickel or platinum counter
electrode. The (nano)structures are formed inside the plurality of
spaced (nano)channels of the template and may form longitudinally
aligned spaced (nano)wires or (nano)pillars or a three-dimensional
network comprising longitudinally aligned spaced (nano)wires and
interconnecting (nano)structures between the spaced (nano)wires,
depending on the architecture of the (nano)channels of the
template. The length of the (nano)wires can be controlled by
controlling the time of deposition. For instance, it was
experimentally found that deposition of nickel at 10 mA/cm.sup.2
for 150 s inside the channels of a porous template formed from
copper doped aluminum leads to the formation of 2 micrometers high
interconnected nickel (nano)wires.
[0162] For example, in a method 200 according to embodiments of the
third aspect of the present disclosure, a catalyst material such as
for example gold may first be provided at the plurality of
(nano)channel bottoms of the template, e.g. by plating, and
afterwards a semiconductor functional material, such as for example
Si, Ge, InP, GaP, or GaAs may be deposited within the
(nano)channels, e.g. by Chemical Vapor Deposition, to thereby form
a plurality of semiconducting (nano)wires inside the plurality of
(nano)channels.
[0163] For example, in a method 200 according to embodiments of the
third aspect of the present disclosure, a Metal-Insulator-Metal
stack may be deposited within the plurality of (nano)channels, for
example by Atomic Layer Deposition. In such embodiments the
insulator material may for example comprise alumina or HfO.sub.2,
and the metal layer may for example comprise TiN or Ru, the present
disclosure not being limited thereto.
[0164] Although in some embodiments of the third aspect of the
present disclosure the plurality of (nano)structures are aligned
longitudinally with their longitudinal direction Y substantially
orthogonal to the valve metal layer (substrate) surface, i.e.
substantially orthogonal to direction X, the present disclosure is
not limited thereto. In embodiments of the present disclosure the
longitudinal direction of the plurality of spaced (nano)structure
may make an angle of from for example 60.degree. to 90.degree. with
the substrate surface on which the (nano)wires abut. In some
embodiments , this angle is from 80.degree. to 90.degree., e.g.
substantially 90.degree., i.e. substantially orthogonal.
[0165] According to a fourth aspect, the present disclosure related
to an entity comprising a substrate and a plurality of spaced
structures on the substrate, the plurality of spaced structures
being aligned longitudinally along a first direction, as may be
obtained using a method according to an embodiment of the third
aspect of the present disclosure. FIG. 11, FIG. 12A and FIG. 12B
each schematically show a cross section of an example of an entity
according to an embodiment of the fourth aspect of the present
disclosure. FIG. 12A illustrates an example of an entity 50
comprising a substrate 10 and a plurality of spaced structures 51
being aligned longitudinally along a first direction forming an
angle of about 90.degree. with respect to a surface of the
substrate 10, i.e. being oriented substantially orthogonal to a
surface of the substrate. FIG. 12B illustrates an example of an
entity 50 comprising a substrate 10 and a plurality of spaced
structures 51 being aligned longitudinally along a first direction
forming an angle of about 90.degree. with respect to a surface of
the substrate 10, and further comprising a plurality of
interconnecting structures 52 oriented along a second direction
substantially orthogonal to the first direction.
[0166] According to a fifth aspect, the present disclosure relates
to a device comprising an entity according to an embodiment of the
fourth aspect of the present disclosure. Examples of devices
wherein such an entity may be used are batteries, fuels cells,
sensors, supercapacitors (such as Metal-Insulator-Metal
supercapacitors), electrolyzers, photo-electrolyzers, and chemical
reactors.
[0167] According to a sixth aspect, the present disclosure relates
to a method for forming a layer of functional material on an
electrically conductive substrate. A method according to an
embodiment of the sixth aspect of the present disclosure may for
example be used for depositing an active electrode material on, for
example, a transition metal substrate. An example of a method 300
according to the sixth aspect of the present disclosure is
schematically illustrated in FIG. 13, showing a flow chart
comprising an example process sequence, and in FIG. 14 to FIG. 16,
schematically showing cross sections illustrating results of
successive steps of the process sequence of FIG. 13.
[0168] As illustrated in the example shown in FIG. 13, a method 300
according to an embodiment of the sixth aspect of the present
disclosure comprises depositing 301 an interlayer on an
electrically conductive substrate. The interlayer may for example
have a thickness in the range between 0.5 nm and 30 nm, for example
in the range between 0.5 nm and 5 nm, e.g. in the range between 0.5
nm and 3 nm.
[0169] In embodiments of the sixth aspect of the present disclosure
the material of the interlayer is selected to provide protection
against thermal degradation such as for example oxidation (i.e. to
prevent oxidation) of the underlying electrically conductive
substrate material during further process steps. For example, the
material of the interlayer may be selected to have a low
diffusivity of oxygen. It may be selected to be chemically inert
with respect to a functional material precursor plating bath, to
thereby prevent electro-oxidation of the underlying substrate
material, e.g. transition metal, during electrodeposition. It may
be selected to be chemically inert with respect to a layer of
functional material precursor being deposited thereon in a further
process step and/or being annealed in a further process step, to
thereby prevent thermal oxidation of the underlying metal. In the
context of the present disclosure, a low diffusivity of oxygen may
refer to an oxygen diffusivity lower than the oxygen diffusivity in
NiO at temperatures in the range between 300.degree. C. and
500.degree. C. In embodiments of the sixth aspect of the present
disclosure the functional material precursor layer may for example
be an electrode material precursor layer and the layer of
functional material formed on the electrically conductive substrate
may for example be an active electrode material, such as e.g. an
active cathode material or an active anode material of a
solid-state battery cell or battery.
[0170] In embodiments according to the sixth aspect of the present
disclosure different interlayers may be combined, i.e. a stack of
different types of interlayers may be deposited, to thereby provide
protection of the substrate against both thermal oxidation and
electro-oxidation.
[0171] The interlayer may for example comprise a transition metal
oxide, a noble metal or a noble-metal oxide. For example, the
interlayer may comprise NiO.sub.x, Cr.sub.2O.sub.3, TiO.sub.2, RuO,
RuO.sub.2, Ru, Au, or Pt, the present disclosure not being limited
thereto. For example, a transition metal oxide interlayer such as a
nickel oxide interlayer or a chromium oxide interlayer may be
deposited using an electrodeposition process, e.g. in a weakly
basic or basic solution having a pH in the range of 7 to 12. For
example, the interlayer 31 may be deposited by immersing the
substrate in a 0.1 M-1M solution of sodium citrate and applying a
constant anodic current, for example in the range between 1
mA/cm.sup.2 and 100 mA/cm.sup.2 between the substrate (e.g.
comprising a plurality of nickel (nano)wires) and a metallic
counter electrode, for example for 1 to 10 minutes.
[0172] In particular, in embodiments wherein the electrically
conductive substrate is a transition metal substrate the interlayer
may substantially prevent or reduce oxidation of the transition
metal during further process steps (e.g. for fabricating a battery
cell). For example, it may prevent dissolution of nickel
(nano)structures during deposition of a MnO.sub.x cathode precursor
material layer, for example by anodic electrodeposition, and/or it
may improve the resistance of nickel (nano)structures against
oxidation during later thermal treatments, such as for example
annealing for activating the layer of cathode precursor
material.
[0173] A method according to embodiments of the sixth aspect of the
present disclosure may be used for conformally forming a layer of
active cathode material on a structure comprising a plurality of
spaced (nano)structures, e.g. on a plurality of spaced (nano)wires
or a plurality of spaced (nano)tubes, e.g. as may be formed in
accordance with a method 200 of the third aspect of the present
disclosure, for example on a plurality of spaced (nano)structures
formed of an electrically conductive transition metal. Some
examples of such a structure (three-dimensional substrate) are
schematically illustrated in FIG. 11, FIG. 12A, and FIG. 12B, but
the present disclosure is not limited thereto.
[0174] When referring to a substrate in the context of the sixth
aspect of the present disclosure, an electrically conductive
substrate is indicated. This includes at one hand substrates or
structures entirely made of an electrically conductive material,
and at the other hand also substrates or structures comprising
different materials or different material layers, with an
electrically conductive layer, such as for example a nickel layer,
being exposed at a surface thereof. An example of an electrically
conductive substrate, more in particular a three-dimensional
electrically conductive substrate on which layer of active cathode
material may be formed in a sixth aspect of the present disclosure
is schematically illustrated in FIG. 11, FIG. 12A, and FIG.
12B.
[0175] FIG. 14 schematically shows an electrically conductive
substrate 60, after deposition 301 of an interlayer 41 according to
a method of the sixth aspect of the present disclosure.
[0176] In a next step, after deposition of the interlayer 41, a
method 300 according to the sixth aspect of the present disclosure
comprises depositing 302 (FIG. 13) a functional material precursor
layer on the interlayer 41. The functional material precursor layer
may for example be conformally deposited by potentiostatic or
galvanic electrodeposition, such as anodic electrodeposition. FIG.
15 illustrates the structure after conformal deposition 302 of a
functional material precursor layer 42 on the interlayer 41. A
conformally deposited layer is a layer with a uniform thickness,
exactly following the topography of the underlying layer.
[0177] In a subsequent step, a method 300 according to the sixth
aspect of the present disclosure comprises activating 302 (FIG. 13)
the functional material precursor layer 42 by annealing, to thereby
form the layer of functional material 43. The resulting structure
is schematically illustrated in FIG. 16, showing the electrically
conductive substrate 60, in the example comprising a plurality of
electrically conductive (nano)structures 61, being conformally
coated with a layer of functional material 43, the layer of
functional material 43 being provided over the interlayer 41.
[0178] The functional material precursor layer 42 may for example
be a layer of cathode precursor material, for example comprising
manganese oxide, manganese dioxide, cobalt oxide, manganese nickel
oxide, iron phosphate. The layer of functional material 43 may for
example be a layer of active cathode material, for example
comprising lithium manganese oxide, lithium cobalt oxide, lithium
iron phosphate, or lithium sulphide, the present disclosure not
being limited thereto.
[0179] For example, depositing 302 a layer of cathode precursor
material 42 on the interlayer 41 may comprise depositing a
manganese dioxide (MnO.sub.2) layer on the interlayer by applying a
constant anodic current (e.g. in the range between 1 mA/cm.sup.2
and 100 mA/cm.sup.2) between the electrically conductive substrate
and a metallic counter electrode, after immersing the substrate
with the interlayer in a solution containing for example 0.1M to
10M MnSO.sub.4, e.g. 0.1M to 1M MnSO.sub.4, and 0.1M to 10M
H.sub.2SO.sub.4, e.g. 0.1M to 1M H.sub.2SO.sub.4, at a temperature
in the range between 20.degree. C. and 100.degree. C., e.g. between
20.degree. C. and 50.degree. C. The thickness of the layer of
cathode precursor material may be controlled by controlling the
time of electrodeposition. A layer of MnO.sub.x material deposited
as described hereinabove typically has a porosity in the range
between 10% and 80%. Such a porosity may allow for the
accommodation of an ion precursor for activating the layer of
cathode precursor material (MnO.sub.x), such as for example a
lithium containing precursor for conversion into lithiated
manganese oxide. The porosity may allow for the accommodation of an
electrolyte, which may be provided in a further process step.
[0180] Activating 302 the layer of cathode precursor material by
annealing comprises activating the layer of cathode precursor
material for ion insertion/extraction. This annealing may be done
in the presence of an ion containing precursor, such as for example
a lithium containing precursor, a sodium containing precursor,. or
a magnesium containing precursor, to thereby form a layer of active
cathode material. This activating step may for example comprise
coating the layer of cathode precursor material with a
lithium-containing precursor such as a lithium-containing salt and
afterwards annealing, for example annealing at a temperature in the
range between 250.degree. C. and 600.degree. C.
[0181] Examples are provided hereinbelow, which illustrate
experiments in which a method according to embodiments of the sixth
aspect of the present disclosure was used for forming a layer of
active cathode material on an electrically conductive transition
metal substrate. These examples are provided for illustrating
features of embodiments of the third aspect of the present
disclosure, and to aid the skilled person in reducing the
disclosure to practice. However, these examples should not be
construed as limiting the disclosure in any way.
[0182] The formation of the NiO containing interlayer was found to
show a self-terminating behavior. The thickness of this interlayer
was found to be limited to about 1 nm.
[0183] It was experimentally shown that the interlayer 41 may
prevent electro-oxidation of the underlying nickel substrate 40
during subsequent MnO.sub.x electroplating, while the deposition of
MnO.sub.x by electroplating is still possible.
[0184] This is illustrated in FIG. 17, showing potential transients
as measured during galvanostatic deposition of a MnO.sub.x cathode
precursor layer on Ni nano-mesh samples. The samples used in the
experiments comprise a 3.3 micrometer thick Ni nano-mesh layer on a
TiN/Si wafer. For a first part (1) of the samples, an interlayer 41
was provided on the Ni nano-mesh layer, by electrodeposition in a
0.4M sodium citrate solution at 30.degree. C. and by subsequent
application of an anodic current at 2.4 mA/cm.sup.2 and 6
mA/cm.sup.2 current density for 60 s each. A Pt counter electrode
was used. For a second part (2) of the samples no interlayer was
provided, leaving the Ni nano-mesh layer exposed. The galvanostatic
deposition of MnO.sub.x was done in a 0.3M MnSO.sub.4+0.55M
H.sub.2SO.sub.4 bath at 30.degree. C. using a current density of 16
mA/cm.sup.2 footprint (or 0.16 mA/cm.sup.2 of nano-mesh real area).
The Ni nano-mesh layer acted as a working electrode, a platinum
mesh was used as a counter electrode and Ag/AgCl as a reference
electrode.
[0185] The curve labeled (b) in FIG. 17 shows potential transients
as measured on the Ni nano-mesh substrate covered with an
interlayer 41, according to an embodiment of the third aspect of
the present disclosure. The curve corresponds to the MnO.sub.x
potential and illustrates MnO.sub.x deposition on the Ni nano-mesh
substrate. A SEM analysis did not show any visible degradation of
the nano-mesh. The curve labeled (a) in FIG. 17 shows potential
transients as measured on the Ni nano-mesh substrate on which no
interlayer was provided and wherein the Ni was thus exposed to the
electroplating solution. It corresponds to the potential of Ni
dissolution. A SEM analysis showed degradation of the Ni nano-mesh,
and did not reveal any MnO.sub.x deposition.
[0186] This is further illustrated in FIG. 18, showing results of
cyclic voltammetry experiments. In these experiments, samples
comprising a planar 150 nm thick Ni layer provided by Physical
Vapor Deposition on top of a 150 nm thick TiN layer on a Si wafer
were used. The sample labeled (a) in FIG. 18 was cleaned with
acetone and IPA and dried with N.sub.2, while the sample labeled
(b) was cleaned with 20% HCl, water and IPA and dried with N.sub.2.
An interlayer was subsequently provided on sample (b) by
electrochemical deposition. An anodic current of 6 mA/cm.sup.2 was
passed through the nickel layer immersed in a sodium citrate bath
at 30.degree. C., for 180 s. It was found that this resulted in a
very thin layer of NiO/Ni(OH).sub.2, possibly functionalized with
citrate moieties, formed on the surface of nickel layer:
Ni+3H.sub.2O.fwdarw.NiO+2e.sup.-+2H.sub.3O.sup.+. For the
electrodeposition of a MnO.sub.x layer the samples were used as a
working electrode, a platinum mesh was used as a counter electrode
and Ag/AgCl (3M KCL) was used as a reference electrode. The
solution consisted of 0.3M MnSO.sub.4 and 0.55M H.sub.2SO.sub.4.
The cyclic voltammograms shown in FIG. 18 were recorded between the
open circuit potential of the working electrode and 1.5 V vs
Ag/AgCl, at a scanning speed of 10 mV/s, at 25.degree. C. Curves
labeled (a) correspond to a structure without an interlayer being
provided before deposition of the MnO.sub.x layer, whereas curves
labeled (b) correspond to a structure having an interlayer provided
thereon before deposition of the MnO.sub.x layer, in accordance
with an embodiment of the third aspect of the present disclosure.
Upon application of anodic potentials, nickel dissolution peaks
between -0.1V and 0.3V can clearly be seen for sample (a) without
an interlayer being provided on the nickel electrode, and no nickel
dissolution is visible for sample (b) having a NiO interlayer
between the nickel electrode and the MnO.sub.x active cathode
material. No MnO.sub.x deposition was observed for sample (a). This
illustrates that the anodic dissolution of nickel in the acidic
medium is more thermodynamically and kinetically favorable than
deposition of MnO.sub.x.
[0187] It was further experimentally observed that the type of the
interlayer 41 applied to the metallic substrate influences the
conformality of a further coating provided thereon, such as of the
MnO.sub.x cathode precursor material. This is demonstrated in the
following example of the electrodeposition of manganese oxides
(MnO.sub.x) from acidic solution of MnSO.sub.4 on a Ni nano-mesh
substrate (i.e. an interconnected Ni nanowire substrate). Three
samples were examined. The first sample (a) was obtained from a Ni
nano-mesh having a NiO interlayer thereon of about 2 nm, formed by
anodic electropassivation of the nano-mesh in 0.4 M sodium citrate.
MnO.sub.x was subsequently electrodeposited thereon from a 0.3 M
MnSO.sub.4+0.55 M H.sub.2SO.sub.4 electroplating bath, using an
anodic current density of 16 mA/cm.sup.2 and a plating time of 70
s. For the second sample (b), a MnO.sub.x interlayer was formed on
a Ni nano-mesh by a redox ALD method (e.g. as described in patent
application EP18174756). MnO.sub.x was subsequently
electrodeposited thereon from a 0.3 M MnSO.sub.4+0.55M
H.sub.2SO.sub.4 electroplating bath, using an anodic current
density of 16 mA/cm.sup.2 and a plating time of 50 s. The third
sample (c) was a control sample and had no interlayer on the Ni
nano-mesh. MnO.sub.x was electrodeposited thereon from a 0.3 M
MnSO.sub.4+0.55 M H.sub.2SO.sub.4 electroplating bath, using an
anodic current density of 16 mA/cm.sup.2 and a plating time of 70
s.
[0188] The conformality of the MnO.sub.x coating in each sample was
assessed using Scanning Electron Microscopy (SEM), corresponding
SEM images are depicted in FIGS. 21A-21C. In the first sample, as
seen in FIG. 21A, the deposition on the NiO interlayer resulted in
nonconformal layers of MnO.sub.x, as indicated by the bright
uncoated parts of the nano-mesh which remain visible in the SEM
image. In the second sample, the deposition on the MnO.sub.x
interlayer resulted in conformal layers of MnO.sub.x with adhesion
to the nickel nano-mesh, as indicated by the uniform coating around
individual nanowires in FIG. 21B and the absence of the bright
spots indicative of uncoated Ni. In the third sample, the
deposition on the nano-mesh without interlayer present did not
result in the formation of MnO.sub.x, as indicated by the lack of
any visible coating on the brightly colored nano-mesh in FIG. 21C.
Furthermore, the deposition on the nanowires without interlayer
resulted in degradation of the nano-mesh, which was attributed to
the anodic dissolution of nickel during the electrodeposition.
[0189] From the above, we can deduce that the interlayer choice can
play a significant role in guaranteeing good adhesion and
conformality of the electrodeposited layers. It is believed that
the adhesion and conformality of the electrodeposited layer is
achieved by matching the chemical character and/or the
crystallographic structure of the interlayer and the layer
deposited thereon. As such, the interlayer may consist of the same
material as the material to be deposited (e.g. to be
electrodeposited); such as an MnO.sub.x interlayer for the
electrochemical deposition of MnOx or a TiO.sub.2 interlayer for
the electrochemical deposition of TiO.sub.2.
[0190] In embodiments of a method according to the sixth aspect of
the present disclosure, the interlayer 41 may further protect the
underlying metal, e.g. nickel, for oxidation during later annealing
steps. For example, the step of activating 303 the layer of cathode
precursor material 42 may comprise lithiation (activation for
lithium insertion/extraction), resulting in conversion of the
cathode precursor material (e.g. MnO.sub.x) to a lithium-containing
active cathode material (e.g. manganese oxide (LMO)). The
lithiation may comprise an electrochemical conversion or a
solid-state conversion. The lithiation step may for example
comprise coating the MnO.sub.x layer with a lithium-containing salt
(e.g. Li.sub.2CO.sub.3, LiOH, LiNO.sub.3) and annealing at an
elevated temperature, for example at a temperature in the range
between 250.degree. C. and 600.degree. C., to form electroactive
lithium manganese oxide. It was experimentally found that, due to
the oxidizing nature of MnO.sub.x, upon annealing in a nitrogen
atmosphere of a sample comprising a MnO.sub.x layer being provided
directly on a substrate comprising nickel nanowires, the nickel
nanowires were oxidized. A relatively thick nickel oxide layer was
formed (e.g. 5 nm to 20 nm thick, corresponding to 25% to 100% of
the nanowires diameter). The reaction can be written as
follows:
yNi+2MnO.sub.x.fwdarw.yNiO+MnO.sub.(x-0.5y)
[0191] where 1<x.ltoreq.2 and y.ltoreq.-2(1-x).
[0192] In most extreme cases (longer annealing times or higher
temperatures), complete oxidation of nickel (nano)wires was
observed. Nickel oxide is a p-type semiconductor and thus is not
suitable as a material for a battery current collector, which
should be conductive for both negative and positive currents.
[0193] By providing an interlayer 41 according to embodiments of
the sixth aspect of the present disclosure, such oxidation of the
current collector material (such as nickel) may be substantially
avoided. Embodiments according to the sixth aspect of the present
disclosure may include an interlayer that forms an effective oxygen
diffusion barrier which shields the underlying metal, e.g. nickel,
from oxidation, e.g. by the active cathode material precursors,
e.g. MnO.sub.x precursors. The interlayer may be a thin layer, e.g.
having at thickness smaller than 30 nm, preferably e.g. smaller
than 5 nm, in view of not adding excessive volume to the electrode
and to have reasonable electronic conductance.
[0194] The interlayer can for example consist of nickel oxide as
described above, or it can consist of a transition metal such as
titanium or chromium, or a noble metal such as ruthenium, gold, or
platinum. The interlayer may also be formed with oxides of such
metals. The metal or metal oxide interlayers may be coated on
(nano) structures, e.g. nickel (nano)structures, either by
electrodeposition or by gas phase methods such as ALD (Atomic Layer
Deposition) or CVD (Chemical Vapor Deposition). The interlayer can
in general be deposited by various methods, such as but not limited
to, electrodeposition, physical vapor deposition, chemical vapor
deposition or atomic layer deposition. Atomic layer deposition may
yield the highest conformality of the deposited interlayer on high
aspect ratio surfaces and may thus for that reason be used. After
coating, an additional step of annealing in a reducing atmosphere
(e.g. H.sub.2/Ar, forming gas) may optionally be done to reduce the
metal oxide to its corresponding metallic form.
[0195] In an embodiment, a spinel LiMn.sub.2O.sub.4 layer of active
cathode material may be formed. After deposition of a layer of
MnO.sub.x as described above, the substrate with deposited
MnO.sub.x may be immersed in a solution containing lithium salts
such as 0.1M to 3M LiOH or LiNO.sub.3 or Li2CO.sub.3, and subjected
to spin coating for removal of excess solution. Next an annealing
step, e.g. at 350.degree. C., may be done to form spinel phase
LiMn.sub.2O.sub.4. The excess of lithium salt may be further
removed by washing in water. The so-formed active material
typically has a porosity between 10% and 80% and allows
accommodating a volume of later provided electrolyte material.
[0196] According to a seventh aspect, the present disclosure
relates to a method for fabricating a solid-state battery cell,
wherein the method comprises forming a plurality of electrically
conductive (nano)structures according to an embodiment of the third
aspect of the present disclosure, and forming a first layer of
active electrode material on the plurality of electrically
conductive structures, wherein the first layer of active electrode
material conformally coats surfaces of the plurality of
electrically conductive structures. Next a solid electrolyte layer
is deposited over the layer of active electrode material, and a
second layer of active anode material is formed over the solid
electrolyte layer. One of the first layer of active electrode
material and the second layer of active electrode material forms a
cathode layer and the other one forms an anode layer of the
solid-state battery cell. A current collector layer may be
deposited over the second layer of active electrode material.
[0197] In embodiments according to the seventh aspect of the
present disclosure the substrate comprises an electrically
conductive layer. In embodiments the substrate may consist of an
electrically conductive layer, such as for example a metal foil,
e.g. an aluminum, copper, chromium, or nickel foil. The plurality
of spaced electrically conductive (nano)structures may for example
comprise (nano)wires or (nano)tubes. The plurality of spaced
electrically conductive (nano)structures may for example comprise
nickel, aluminum, copper, or chromium and they may have a
longitudinal direction oriented substantially orthogonal to the
substrate surface. The cathode material may for example contain
manganese (di)oxide (e.g. MnO or MnO.sub.2), lithium manganese
oxide (e.g. LiMn.sub.2O.sub.4, LiMnO.sub.2, or Li.sub.2MnO.sub.3),
lithium manganese nickel oxide, lithium cobalt oxide (e.g.
LiCoO.sub.2 or LiCo.sub.2O.sub.4), lithium nickel oxide (e.g.
LiNiO.sub.2), cobalt (II,III) oxide, lithium manganese phosphate
(e.g. LiMnPO.sub.4), lithium iron phosphate (e.g. LiFePO.sub.4),
lithium cobalt phosphate (e.g. LiCoPO.sub.4), lithium sulfide (e.g.
Li.sub.2S), lithium titanium sulfide (e.g. LiTiS.sub.2), sodium
iron phosphate, tungsten selenide, vanadium pentoxide, molybdenum
disulfide, or sulfur. The layer of active anode material may for
example comprise lithium titanium oxide (e.g.
Li.sub.4Ti.sub.5O.sub.12), metallic lithium, titanium dioxide,
vanadium pentoxide, silicon, graphite, manganese (II) monoxide,
metallic magnesium, metallic sodium, metallic potassium, metallic
germanium or metallic tin. In some embodiments, it may be formed by
a method according to an embodiment of the third aspect of the
present disclosure. The current collector layer may for example
comprise metallic lithium or a foil of nickel, aluminum, copper,
chromium, or zinc, the present disclosure not being limited
thereto.
[0198] In embodiments according to the seventh aspect of the
present disclosure, a solid electrolyte layer is deposited over the
first layer of active electrode material. The solid electrolyte
layer may be deposited conformally over the first layer of active
electrode material or it may be deposited non-conformally, such as
for example with an upper surface that is substantially flat and
substantially parallel to the substrate surface. In embodiments, a
combination of a conformally coated solid electrolyte layer and a
non-conformally coated solid electrolyte layer may be used. For
example, a first solid electrolyte layer may be conformally
deposited over the first layer of active electrode material and
next a second solid electrolyte layer may be non-conformally
deposited over the first solid electrolyte layer. Deposition of a
solid electrolyte layer may for example be done using
electrodeposition, by drop casting an electrolyte precursor
solution and spin coating the excess of the precursor solution, or
by vapor phase deposition such as atomic layer deposition.
[0199] For example, in an embodiment the solid electrolyte layer
may comprise lithium phosphorous oxynitride (LiPON) or a solid
composite electrolyte (e.g. Li.sub.2S--P.sub.2S.sub.5). A solid
LiPON electrolyte layer may for example be deposited by ALD cycling
of lithium tert-butoxide, trimethylphosphate and water, with or
without addition of nitrogen in the deposition chamber. This leads
to impregnation of the cathode active material with the solid-state
electrolyte. Additionally, a solid electrolyte layer, for example
having a thickness in the range between 50 nm and 1 micrometer may
be deposited on top of the stack, e.g. by sputter coating or spin
coating. Following the additional deposition, the stack may be
subjected to a heat treatment, for example at a temperature in the
range between 50.degree. C. and 350.degree. C., for enhanced
gelification or sintering purposes.
[0200] In embodiments according to the seventh aspect of the
present disclosure, a second layer of active electrode material is
formed over the solid electrolyte layer. The second layer of active
electrode material may be deposited conformally over the solid
electrolyte layer or it may be deposited non-conformally, such as
for example with an upper surface that is substantially flat and
substantially parallel to the substrate surface. In embodiments, a
combination of a conformally coated second layer of active
electrode material and a non-conformally coated layer may be used.
Deposition of a second layer of active electrode material may for
example be done using vapor phase deposition, such as DC
sputtering, thermal evaporation, atomic layer deposition or
chemical vapor deposition. For example, in an embodiment, the
second active electrode material may be metallic lithium. The layer
of metallic lithium may for example have a thickness in the range
between 0.5 micrometer and 10 micrometers. It may for example be
deposited by thermal evaporation of lithium onto the solid
electrolyte layer. In another embodiment, the second layer of
active electrode material may for example comprise spinel
Li.sub.4Ti.sub.5O.sub.12 or amorphous TiO.sub.2. These active anode
materials may for example be deposited by DC sputtering or ALD
coating, followed by annealing (sintering), e.g. at a temperature
in the range between 200.degree. C. and 400.degree. C. If some
embodiments a thin electrically conductive layer, such as an
aluminum layer or a nickel layer, e.g. having a thickness in the
range between 50 nm and 1 micrometer, may be deposited on top of
the layer of active anode material, for example by DC sputtering or
thermal evaporation.
[0201] The battery cell thus obtained may be coated with a polymer
layer such as a polydimethoxysilane (PDMS) layer or a poly(methyl
methacrylate) layer, for example with a thickness in the range
between 100 nm and 5 micrometer, to protect it from air and
moisture. The polymer layer may for example be applied by spin
coating, blade coating, or drop casting, followed by curing at a
temperature for example in the range between 20.degree. C. and
150.degree. C.
[0202] According to an eighth aspect, the present disclosure is
related to a method for fabricating a solid-state battery cell, the
method comprising: forming a plurality of spaced electrically
conductive structures on a substrate; forming a first layer of
active electrode material on the plurality of spaced electrically
conductive structures according to a method of the sixth aspect of
the present disclosure, wherein the first layer of active electrode
material conformally coats surfaces of the plurality of
electrically conductive structures; depositing a solid electrolyte
layer over the first layer of active electrode material; and
depositing a second layer of active electrode material over the
solid electrolyte layer. One of the first layer of active electrode
material and the second layer of active electrode material forms a
cathode layer and the other one forms an anode layer of the
solid-state battery cell. A current collector layer may be
deposited over the second layer of active electrode material.
[0203] According to a ninth aspect, the present disclosure is
related to a method for fabricating a solid-state battery. A method
according to the ninth aspect of the present disclosure comprises:
fabricating a plurality of solid-state battery cells in accordance
with an embodiment of the seventh or the eighth aspect of the
present disclosure; and forming a stack of the plurality of
solid-state battery cells with a solid electrolyte being provided
in between neighboring solid-state battery cells.
[0204] According to a tenth aspect, the present disclosure is
related to a solid-state battery cell. An example of a solid-state
battery cell according to an embodiment of the tenth aspect of the
present disclosure is schematically illustrated in FIG. 19. In the
example shown, the solid-state battery cell 80 comprises a
plurality of spaced electrically conductive structures 70. More in
particular, FIG. 19 shows an embodiment wherein the plurality of
spaced electrically conductive structures 70 is aligned along a
direction substantially orthogonal to a substrate 10 on which those
structures are provided. This is only an example, and in
embodiments of the tenth aspect of the present disclosure other
orientations, shapes and/or configurations may be used. As
illustrated in FIG. 19, the plurality of spaced electrically
conductive structures 70 is conformally coated with an interlayer
71, the interlayer 71 being conformally coated with a first layer
of active electrode material 72. The solid-state battery cell 80
further comprises a solid electrolyte layer 73 over the first layer
of active electrode material 72. In the example shown, the solid
electrolyte layer 73 is provided non-conformally and has an upper
surface that is substantially flat and substantially parallel to a
surface of the substrate 10. However, this is only an example and
the present disclosure is not limited thereto. The solid-state
battery cell 80 further comprises a second layer of active
electrode material 74 over the solid electrolyte layer 73.
[0205] In a solid-state battery cell 80 according to an embodiment
of the tenth aspect of the present disclosure the interlayer 71
may, for example, comprise a transition metal oxide layer, a noble
metal layer, or a noble-metal oxide layer. It may, for example,
have a thickness in the range between 0.5 nm and 30 nm. One of the
first layer of active electrode material 72 and the second layer of
active electrode material 74 forms a cathode layer and the other
one forms an anode layer of the solid-state battery cell 80.
[0206] Battery cells of the tenth aspect of the present disclosure
may further be stacked into batteries or battery packs, for example
for increasing the delivered electrical potential or current of the
device upon discharging.
[0207] According to an eleventh aspect, the present disclosure
relates to a solid-state battery comprising at least one
solid-state battery cell in accordance with an embodiment of the
tenth aspect of the present disclosure. FIG. 20 schematically shows
a cross-section of an example of such a solid-state battery 90. In
the example shown in FIG. 20, the solid-state battery 90 comprises
a single solid-state battery cell 80 corresponding to the example
illustrated in FIG. 19. However, the present disclosure is not
limited thereto. Further, a solid-state battery 90 in accordance
with the eleventh aspect of the present disclosure may comprise
more than one, for example two, for example a plurality of
solid-state battery cells 80 (not illustrated).
[0208] In the solid-state battery shown in FIG. 20, the plurality
of electrically conductive structures 70 have the function of a
first current collector of the battery 90. The solid-state battery
90 further comprises a second current collector 75 over the second
layer of active electrode material 74, and an encapsulation layer
76.
[0209] The foregoing description details certain embodiments of the
disclosure. It will be appreciated, however, that no matter how
detailed the foregoing appears in text, the disclosure may be
practiced in many ways. It should be noted that the use of
particular terminology when describing certain features or aspects
of the disclosure should not be taken to imply that the terminology
is being re-defined herein to be restricted to including any
specific characteristics of the features or aspects of the
disclosure with which that terminology is associated.
[0210] It is to be understood that although example embodiments,
specific constructions and configurations, as well as materials,
have been discussed herein for methods and devices according to the
present disclosure various changes or modifications in form and
detail may be made without departing from the scope of this
disclosure. For example, steps may be added or deleted to methods
described within the scope of the present disclosure.
[0211] Whereas the above detailed description as well as the
summary of the disclosure has been focused on a method for
fabricating a device, the present disclosure also relates to a
device comprising patterned layers obtained using a method
according to any of the embodiments as described above.
* * * * *