U.S. patent application number 15/665142 was filed with the patent office on 2019-01-31 for continuous production of binder and collector-less self-standing electrodes for li-ion batteries by using carbon nanotubes as an additive.
The applicant listed for this patent is HONDA MOTOR CO., LTD., NANOSYNTHESIS PLUS, LTD.. Invention is credited to Avetik Harutyunyan, Neal Pierce, Elena Mora Pigos.
Application Number | 20190036102 15/665142 |
Document ID | / |
Family ID | 62981113 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190036102 |
Kind Code |
A1 |
Pierce; Neal ; et
al. |
January 31, 2019 |
CONTINUOUS PRODUCTION OF BINDER AND COLLECTOR-LESS SELF-STANDING
ELECTRODES FOR LI-ION BATTERIES BY USING CARBON NANOTUBES AS AN
ADDITIVE
Abstract
The present disclosure is directed to a method and apparatus for
continuous production of composites of carbon nanotubes and
electrode active material from decoupled sources. Composites thusly
produced may be used as self-standing electrodes without binder or
collector. Moreover, the method of the present disclosure may allow
more cost-efficient production while simultaneously affording
control over nanotube loading and composite thickness.
Inventors: |
Pierce; Neal; (Beavercreek,
OH) ; Harutyunyan; Avetik; (Columbus, OH) ;
Pigos; Elena Mora; (Galena, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HONDA MOTOR CO., LTD.
NANOSYNTHESIS PLUS, LTD. |
Tokyo
Columbus |
OH |
JP
US |
|
|
Family ID: |
62981113 |
Appl. No.: |
15/665142 |
Filed: |
July 31, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/583 20130101;
H01M 4/133 20130101; C01P 2006/40 20130101; Y10S 977/842 20130101;
B82Y 40/00 20130101; Y10S 977/75 20130101; H01M 4/505 20130101;
Y02E 60/10 20130101; Y10S 977/948 20130101; C01B 32/16 20170801;
H01M 4/0419 20130101; H01M 4/52 20130101; B82Y 30/00 20130101; C01G
53/50 20130101; H01M 4/525 20130101; H01M 4/625 20130101; H01M
4/485 20130101; C01B 32/162 20170801; C01B 2202/02 20130101 |
International
Class: |
H01M 4/04 20060101
H01M004/04; H01M 4/505 20060101 H01M004/505; H01M 4/525 20060101
H01M004/525; H01M 4/62 20060101 H01M004/62; C01B 32/16 20060101
C01B032/16; C01G 53/00 20060101 C01G053/00 |
Claims
1. A method of making a self-standing electrode, the method
comprising: fluidizing an electrode active material; and
co-depositing the fluidized electrode active material and
single-walled carbon nanotubes onto a movable porous flexible
substrate to form a self-standing electrode that is a composite of
the electrode active material and the single-walled carbon
nanotubes.
2. The method of claim 1, further comprising synthesizing the
single-walled carbon nanotubes in a carbon nanotube synthesis
reactor.
3. The method of claim 1, wherein the electrode active material is
selected from graphite, hard carbon, lithium metal oxides, lithium
iron phosphate, and metal oxides.
4. The method of claim 1, wherein the carbon nanotubes and the
electrode active material do not contact each other until they are
co-deposited onto the substrate.
5. The method of claim 1, wherein the fluidizing of the electrode
active material comprises distributing a carrier gas through,
sequentially, a porous frit and a bed of the electrode active
material, in an active material container, to form an aerosolized
electrode active material.
6. An apparatus for producing a self-standing electrode, the
apparatus comprising: a carbon nanotube synthesis reactor
configured to synthesize carbon nanotubes; an active material
container configured to fluidize an electrode active material; and
a movable porous flexible substrate configured to collect the
carbon nanotubes and the fluidized electrode active material and
form the self-standing electrode comprising a composite of the
carbon nanotubes and the electrode active material.
7. The apparatus of claim 6, wherein the active material container
comprises: a porous frit; and a vertical shaker.
8. The apparatus of claim 6, wherein the movable porous flexible
substrate is connected to a roll-to-roll system.
9. The apparatus of claim 6, wherein the electrode active material
is selected from graphite, hard carbon, lithium metal oxides,
lithium iron phosphate, and metal oxides.
Description
JOINT RESEARCH AGREEMENT
[0001] The presently claimed invention was made by or on behalf of
the below listed parties to a joint research agreement. The joint
research agreement was in effect on or before the date the claimed
invention was made, and the claimed invention was made as a result
of activities undertaken within the scope of the joint research
agreement. The parties to the joint research agreement are 1) Honda
Research Institute USA, Inc.; and 2) NanoSynthesis Plus, Ltd.
BACKGROUND
[0002] Single-walled carbon nanotubes (SWNTs) as additives in
various matrices has become one of the most intensively studied
areas for applications, owing to their excellent electrical and
mechanical properties and high aspect ratio, which is crucial for
composite materials. Among various applications, the exploitation
of SWNTs as an additive material for performance enhancement of
battery electrodes is very promising. The core of mixing
technologies is based on liquid process and includes five required
steps: a) synthesis of nanotubes, b) dispersion of nanotubes in the
proper solvent (de-aggregation), c) functionalization of the
nanotube surfaces (protecting against aggregation), d) mixing with
binder, and e) mixing with active material (preparing slurry).
These preferences are not only expensive, but they also degrade
nanotube properties; for example, dispersion by ball milling,
sonication, etc. leads to the inevitable reduction of aspect ratio
and the introduction of defects, and as a result, more nanotube
loading (weight %) is required for improved performance.
SUMMARY
[0003] In some embodiments, the present disclosure is directed to a
method of making a self-standing electrode, the method comprising
fluidizing an electrode active material; and co-depositing the
fluidized electrode active material and single-walled carbon
nanotubes onto a movable porous flexible substrate to form a
self-standing electrode that is a composite of the electrode active
material and the single-walled carbon nanotubes.
[0004] In some embodiments, the present disclosure is directed to
an apparatus for producing a self-standing electrode, the apparatus
comprising a carbon nanotube synthesis reactor configured to
synthesize carbon nanotubes; an active material container
configured to fluidize an electrode active material; a movable
porous flexible substrate configured to collect the carbon
nanotubes and the fluidized electrode active material and form the
self-standing electrode comprising a composite of the carbon
nanotubes and the electrode active material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic block diagram illustrating an
exemplary method of making a self-standing electrode according to
an embodiment of the present disclosure.
[0006] FIG. 2 is a flow diagram illustrating an exemplary apparatus
for making a self-standing electrode according to an embodiment of
the present disclosure.
[0007] FIG. 3 is a schematic view illustrating a vessel according
to an embodiment of the present disclosure.
[0008] FIG. 4 shows an example of a schematic of an apparatus
according to an embodiment of the present disclosure.
[0009] FIG. 5 shows an example of an alternate schematic of an
apparatus according to an embodiment of the present disclosure.
[0010] FIG. 6 shows Raman characterization (.lamda.=633 nm) of
carbon nanotubes synthesized according to an embodiment of the
present disclosure.
[0011] FIG. 7 shows Raman characterization (.lamda.=532 nm) of
carbon nanotubes synthesized according to an embodiment of the
present disclosure.
[0012] FIG. 8 shows derivative thermogravimetric analysis (DTG) of
carbon nanotubes synthesized according to an embodiment of the
present disclosure.
DETAILED DESCRIPTION
[0013] The present disclosure provides method and apparatus for the
production of self-standing electrodes. Also provided are
self-standing electrodes comprising a mixture of nanotube and
electrode active materials.
[0014] In an embodiment, a self-standing electrode is prepared by
separately providing aerosolized nanotubes and aerosolized
electrode active material, and directing the aerosolized nanotubes
and the aerosolized electrode active materials to a movable porous
substrate to form a self-standing electrode thereon comprising the
mixed carbon nanotubes and the electrode active material.
[0015] The present disclosure is directed to a method and apparatus
for continuous production of self-standing electrodes for Li-ion
batteries by using a single step co-deposition of carbon nanotubes
and electrode active material on a moving porous substrate. Carbon
nanotubes from the synthesis reactor and the fluidized active
material powder may be directly deposited from a container onto a
porous flexible substrate that is attached to a roll-to-roll system
(FIGS. 4 and 5).
[0016] The resulting deposited layer contains well dispersed
nanotubes in an active electrode material. Independent control of
the nanotube and active material deposition rate allows adjustment
of the ratio of nanotube to active material (weight %). The
thickness of the composite obtained can be controlled, for example
by varying the substrate motion speed for a given deposition rate.
The composite can be removed from the porous substrate, and the
layer is self-supporting, flexible, and can be cut to any desirable
size. The composite can be used as an electrode without any
additional binder or collector (alumina or copper, depending on the
electrode type). The exploitation of this electrode opens the
opportunity to increase the energy and power densities of
batteries. In addition, using decoupled sources for nanotube and
active material powder deposition, as well as implementing a
roll-to-roll system, may allow for control over nanotube loading
(weight %) and composite thickness. Moreover, the method of the
present disclosure can be run continuously, and may provide cost
efficiency.
[0017] In some embodiments, the present disclosure is directed to a
method of making a self-standing electrode, the method comprising
fluidizing an electrode active material; and co-depositing the
fluidized electrode active material and single-walled carbon
nanotubes onto a movable porous flexible substrate to form a
self-standing electrode that is a composite of the electrode active
material and the single-walled carbon nanotubes.
[0018] As used herein, "electrode active material" refers to the
conductive material in an electrode. The term "electrode" refers to
an electrical conductor where ions and electrons are exchanged with
an electrolyte and an outer circuit. "Positive electrode" and
"cathode" are used synonymously in the present description and
refer to the electrode having the higher electrode potential in an
electrochemical cell (i.e. higher than the negative electrode).
"Negative electrode" and "anode" are used synonymously in the
present description and refer to the electrode having the lower
electrode potential in an electrochemical cell (i.e. lower than the
positive electrode). Cathodic reduction refers to a gain of
electron(s) of a chemical species, and anodic oxidation refers to
the loss of electron(s) of a chemical species.
[0019] In a non-limiting example as shown in FIG. 1, self-standing
electrodes for Li-ion batteries are prepared by separately
providing aerosolized carbon nanotubes and aerosolized electrode
active materials at step S100, and directing the aerosolized carbon
nanotubes and the aerosolized electrode active materials to a
porous substrate at step S101 to form a composite self-standing
electrode of a desired thickness thereon that comprises the mixed
carbon nanotubes and the electrode active materials. Optionally,
the self-standing electrode can be treated at step S102 to, for
example, increase the density of the self-standing electrode. The
self-standing electrode is self-supported, flexible, and can
optionally be cut to the desired dimensions of a battery electrode.
The self-standing electrode is optionally free of binder and
optionally can be used without a metal-based current collector
(typically alumina or copper depending on the electrode type).
[0020] The apparatus of providing the aerosolized carbon nanotubes
and the aerosolized electrode active materials is not limited in
any way. In an illustrative example as shown in FIG. 2, an
apparatus 5 for the production of self-standing electrodes is
provided. The carbon nanotubes and the electrode active materials
are added to separate vessels 10A, 10B. The carbon nanotubes and
the electrode active materials may be individually collected from
their respective manufacturing processes and directly or indirectly
introduced from such processes into the vessels 10A, 10B at a
desired ratio for the self-standing electrode. One or more carrier
gases 20A, 20B may then be introduced to the vessels 10A, 10B to
aerosolize the nanotubes and the electrode active materials. The
resulting aerosolized streams 30A, 30B comprising the nanotubes and
the electrode active materials (separately) entrained in the
carrier gas are directed to a movable porous substrate 40, such as
a filter. The carrier gas passes through the movable porous
substrate 40 as gas stream 50 while the mixture of the nanotubes
and the electrode active material is captured on the surface of the
movable porous substrate 40 to form the self-standing electrode 60.
The self-standing electrode 60 can be removed from the movable
porous substrate 40 when it reaches the desired thickness.
[0021] Optionally, the apparatus 5 may include a plurality of
movable porous substrates 40, 41 to allow for the continuous
production of self-standing electrodes 60, 61. Although only two
porous substrates are shown, it is to be understood that any number
of porous substrates may be included in the apparatus 5. In a
non-limiting example, when the flow of the aerosolized streams 30A,
30B across the movable porous substrate 40 produces the
self-standing electrode 60 of the desired thickness, valves 33A,
33B may be adjusted to transfer the flow of the aerosolized streams
30A, 30B to a second movable porous substrate 41. The self-standing
electrode 60 may be removed from the first movable porous substrate
40 during formation of the self-standing electrode 61 on the
movable porous substrate 41. When the flow of the aerosolized
streams 30A, 30B across the second movable porous substrate 41
produces the self-standing electrode 61 of a desired thickness, the
valves 33A, 33B may be adjusted to transfer the flow of the
aerosolized streams 30A, 30B back to the first movable porous
substrate 40. The thickness and/or cross-sectional area of the
self-standing electrode 61 may be the same, or different, than the
cross-sectional area of the self-standing electrode 60. For
example, the self-standing electrode 61 may have a greater
thickness and/or cross-sectional area than the self-standing
electrode 60.
[0022] It is to be understood that a variety of different methods
may be used for automatically switching the valves 33A, 33B to
redirect the flow of the aerosolized streams 30A, 30B from one
movable porous substrate to the other. Illustrative examples of
systems that may be used to adjust the valves 33A, 33B to redirect
the flow of the aerosolized streams 30A, 30B include one or more
sensors for detecting the thickness of the self-standing electrodes
60 and 61, one or more pressure sensors for monitoring a pressure
drop across the movable porous substrates 40 and 41 that
corresponds to a desired thickness of the self-standing electrodes
60 and 61, a timer that switches the valves 33A, 33B after a set
time corresponding to a desired thickness of the self-standing
electrodes 60 and 61 for a given flow rate of the aerosolized
streams 30A, 30B, and any combination thereof; after the one or
more pressure sensors measures a pressure drop associated with the
desired thickness of the self-standing electrode 60 or 61 on porous
substrate 40 or 41, or after the one or more thickness sensors
detect the desired thickness of the self-standing electrode 60 or
61 on porous substrate 40 or 41, or after the timer measures the
set time corresponding to the desired thickness of self-standing
electrode 60 or 61 on porous substrate 40 or 41, the mixture is
redirected from one porous substrate to the other. It is also to be
understood that the movable porous substrates 40 and/or 41 may have
a cross-sectional area that matches the desired cross-sectional
area required for use in the battery cell to be made with the
self-standing electrode 60 and/or 61. Accordingly, the
self-standing electrodes 60 and/or 61 would require no further
processing of the cross-sectional area, such as cutting, before
assembly in the final battery cell.
[0023] It is to be understood that the configuration of the vessels
10A, 10B is not intended to be limited in any way. In an
illustrative example as shown in FIG. 3, the vessel 10A (and/or the
vessel 10B) may be a pneumatic powder feeder, such as a venturi
feeder that includes a hopper 11A for receiving the nanotubes 11A
(and/or a hopper 11B for receiving the electrode active material
11B) therein. The vessel 10A (and/or the vessel 10B) may also
include a rotary valve 12A (and/or 12B) that feeds the nanotubes
12A (and/or the electrode active material 12B) into contact with
the carrier gas 20A that is introduced to the vessel 10A (and/or
the carrier gas 20B that is introduced into the vessel 10B) to form
the aerosolized stream 30A (and/or 30B).
[0024] As shown in FIG. 4, the nanotubes may be provided in an
aerosolized stream 30A directly from the vessel 10A that is
configured as a nanotube synthesis reactor, in parallel with an
aerosolized stream 30B of the electrode active material from the
source 106. Accordingly, the aerosolized stream 30A may be a
product stream exiting the nanotube synthesis reactor. For example,
a carbon source or carbon precursor 130 may be introduced to the
vessel 10A in the presence of one or more carrier gases 20A to form
carbon nanotubes. The aerosolized stream 30A of carbon nanotubes
exits the reactor outlet 175 and travels down a pipe or tube 412 to
a hood 27 where the aerosolized carbon nanotubes are co-deposited
with the aerosolized stream 30B of the electrode active materials
as a self-standing layer 60 onto a porous flexible substrate 40.
Although the pipes leading into the hood 27 are shown to bend at 90
degree angles `.alpha..sub.1, .alpha..sub.2` before reaching hood
27, other angles .alpha..sub.1, .alpha..sub.2 may be formed. In a
non-limiting example, one or more of the angles .alpha..sub.1,
.alpha..sub.2 may be a 180.degree. angle that facilitates flow of
the aerosolized streams 30A, 30B from the hood 27 to the porous
substrate 40, e.g., as shown in FIG. 5. Although not shown, it is
to be understood that more than one porous substrate 40 may be
provided as described with respect to FIG. 2.
[0025] Carrier and fluidizing gases suitable for use with the
present disclosure include, but are not limited to, argon,
hydrogen, nitrogen, and combinations thereof. Carrier gases may be
used at any suitable pressure and at any suitable flow rate to
aerosolize the nanotubes and the electrode active materials and
transport the aerosolized nanotubes and the aerosolized electrode
active materials to the movable porous substrate at a sufficient
velocity to form the self-standing electrode on the surface
thereof. In some embodiments, the carrier gas may be argon,
hydrogen, helium, or mixtures thereof. In some embodiments, the
carrier gas may comprise argon at a flow rate of 850 standard cubic
centimeters per minute (sccm) and hydrogen at a flow rate of 300
sccm.
[0026] The type of nanotubes used in the present disclosure are not
limited. The nanotubes may be entirely carbon, or they made be
substituted, that it is, have non-carbon lattice atoms. Carbon
nanotubes may be externally derivatized to include one or more
functional moieties at a side and/or an end location. In some
aspects, carbon and inorganic nanotubes include additional
components such as metals or metalloids, incorporated into the
structure of the nanotube. In certain aspects, the additional
components are a dopant, a surface coating, or are a combination
thereof.
[0027] Nanotubes may be metallic, semimetallic, or semi-conducting
depending on their chirality. A carbon nanotube's chirality is
indicated by the double index (n,m), where n and m are integers
that describe the cut and wrapping of hexagonal graphite when
formed into a tubular structure, as is well known in the art. A
nanotube of an (m,n) configuration is insulating. A nanotube of an
(n,n), or "arm-chair", configuration is metallic, and hence highly
valued for its electric and thermal conductivity. Carbon nanotubes
may have diameters ranging from about 0.6 nm for single-wall carbon
nanotubes up to 500 nm or greater for single-wall or multi-wall
nanotubes. The nanotubes may range in length from about 50 nm to
about 10 cm or greater.
[0028] The movable porous substrate may be rendered movable by any
suitable means known to those of ordinary skill in the art. In some
embodiments, the movable porous substrate may be a porous flexible
substrate attached to a conveyor belt or a roll-to-roll system,
such as roll-to-roll system 45 shown in FIGS. 4 and 5. The rate of
motion of the movable porous substrate may be controllable, such as
by a computer or manually by an operator. Control of the rate of
motion may enable or facilitate control of the thickness of the
composite obtained. Suitable porous flexible substrates, including
but not limited to a filter or a frit, have pores appropriately
sized so as to not permit passage of the composite. In some
embodiments, the pores may be sized to permit passage of carrier
gases and/or fluidizing gases.
[0029] In a non-limiting example, carbon nanotubes may be
synthesized in a reactor or furnace from a carbon source or carbon
precursor in the presence of a catalyst or catalyst precursor, at a
temperature of about 1000 to about 1500.degree. C., such as about
1300.degree. C.
[0030] The present disclosure is not limited to the type or form of
catalysts used for the production of carbon nanotubes. In various
aspects, the catalyst particles are present as an aerosol. In some
aspects, the catalyst materials are supplied as nanoparticles,
including but not limited to colloidal metallic nanoparticles,
comprising a transition metal, a lanthanide metal, or an actinide
metal. For example, the catalyst may comprise a Group VI transition
metal such as chromium (Cr), molybdenum (Mo), and tungsten (W), or
a Group VIII transition metal such as iron (Fe), cobalt (Co),
nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium
(Os), Iridium (Ir), and platinum (Pt). In some aspects, a
combination of two or more metals are used, for example an iron,
nickel, and cobalt mixture or more specifically a 50:50 mixture (by
weight) of nickel and cobalt. The catalyst may comprise a pure
metal, a metal oxide, a metal carbide, a nitrate salt of a metal,
and/or other compounds containing one or more of the metals
described herein. The catalyst may be added to the reactor at about
0.1 atom % to about 10 atom %, where atom % indicates the
percentage of the number of catalyst atoms with respect to the
total number of atoms in the reactor (catalyst and carbon precursor
atoms).
[0031] Alternatively or in combination, a catalyst precursor may be
introduced, wherein the catalyst precursor can be converted to an
active catalyst under the reactor's conditions. The catalyst
precursor may comprise one or more transition metal salts such as a
transition metal nitrate, a transition metal acetate, a transition
metal citrate, a transition metal chloride, a transition metal
fluoride, a transition metal bromide, a transition metal iodide, or
hydrates thereof. For example, the catalyst precursor may be a
metallocene, a metal acetylacetonate, a metal phthalocyanine, a
metal porphyrin, a metal salt, a metalorganic compound, or a
combination thereof. For example, the catalyst precursor may be a
ferrocene, nickelocene, cobaltocene, molybdenocene, ruthenocene,
iron acetylacetonate, nickel acetylacetonate, cobalt
acetylacetonate, molybdenum acetylacetonate, ruthenium
acetylacetonate, iron phthalocyanine, nickel phthalocyanine, cobalt
phthalocyanine, iron porphyrin, nickel porphyrin, cobalt porphyrin,
an iron salt, a nickel salt, cobalt salt, molybdenum salt,
ruthenium salt, or a combination thereof. The catalyst precursor
may comprise a soluble salt such as Fe(NO3)3, Ni(NO3)2 or Co(NO3)2
dissolved in a liquid such as water. The catalyst precursor may
achieve an intermediate catalyst state in the catalyst particle
growth zone of the reactor, and subsequently become converted to an
active catalyst upon exposure to the nanostructure growth
conditions in the nanostructure growth zone of the reactor. For
example, the catalyst precursor may be a transition metal salt that
is converted into a transition metal oxide in the catalyst particle
growth zone, then converted into active catalytic nanoparticles in
the nanostructure growth zone.
[0032] The catalyst particles may comprise a transition metal, such
as a d-block transition metal, an f-block transition metal, or a
combination thereof. For example, the catalyst particles may
comprise a d-block transition metal such as an iron, nickel,
cobalt, gold, silver, or a combination thereof. The catalyst
particles may be supported on a catalyst support, wherein the
catalyst support may be selected from alumina, silica, zirconia,
magnesia, or zeolites. For example, the catalyst support may be a
nanoporous magnesium oxide support. The catalyst support may be the
same or different from the material selected for the matrix. In
order to have catalyst particles on a catalyst support, the
catalyst support material may be introduced into the catalyst
material prior to adding the catalyst to the reactor. For example,
a solution of the catalyst material, such as a molybdenum/cobalt
mixture, may be combined with a solution of magnesium nitrate,
heated together, and then cooled to produce a catalyst on a
nanoporous MgO support. Alternately, a silica support may be
impregnated with cobalt nitrate and ammonium heptamolybdate and
dried for several hours to produce a cobalt/molybdenum catalyst on
a porous silica support.
[0033] The present disclosure is not limited to the type of carbon
precursors or carbon sources used to form carbon nanotubes such as
one or more carbon-containing gases, one or more hydrocarbon
solvents, and mixtures thereof. Examples of carbon precursors
include, but are not limited to hydrocarbon gases, such as methane,
acetylene, and ethylene; alcohols, such as ethanol and methanol;
benzene; toluene; CO; and CO.sub.2. A fuel for carbon nanotube
synthesis and growth comprises a mixture of one or more carbon
precursors or carbon sources and one or more catalysts or catalyst
precursors.
[0034] The fuel or precursor may be injected at a range of about
0.05 to about 1 ml/min, such as about 0.1 ml/min or about 0.3
ml/min, per injector. In some embodiments, more than one injector
may be used, for example at large scale. The gas flow rate may be
about 0.1 to about 5 L/min of hydrogen and/or about 0.2 to about 2
L/min helium or argon, such as about 5 L/min hydrogen, or about 0.3
L/min hydrogen and about 1 L/min argon. Without wishing to be bound
to any particular theory, helium or argon may be included in the
carrier gas to dilute the hydrogen concentration, for example to
keep the hydrogen concentration below the explosive limit.
Selection of a fuel injection rate and/or a gas flow rate may
depend, for example, on the reactor volume, as will be apparent to
those of ordinary skill in the art. In some embodiments, more than
one reactor may be used in conjunction. In some embodiments, the
reactor temperature profile consists of a starting low temperature,
an increase to a peak or a maximum, and then a decrease, preferably
to the starting low temperature. Without wishing to be bound by any
particular theory, for a given reactor temperature profile, the
injector position inside the reactor should be correlated with the
precursor temperature so that the precursor evaporates from the
point of injection, without droplet formation or decomposition, as
can be determined by those of ordinary skill in the art,
considering for example the boiling point and decomposition. In
some embodiments, the injector tip may be inserted into the
reactor, for example, by about 8 inches. The injection temperature,
at the tip of the injector, may depend on the reactor or furnace
temperature and upon the depth of insertion of the injector into
the reactor or furnace. In some embodiments, the injection
temperature at the tip of the injector is about 750.degree. C. In
some embodiments, the injector tip is inserted about 8 inches
inside the reactor. The carbon nanotube reactor may be run for any
suitable length of time to obtain the product composition and
thickness desired, as can be determined by those of ordinary skill
in the art, for example as long as there are starting
materials.
[0035] Carbon nanotubes synthesized according to the present
disclosure may be characterized using any suitable means known in
the art, including but not limited to derivative thermogravimetric
analysis (DTG) and Raman spectroscopy, such as for calculation of
the G/D ratio, as is disclosed in U.S. Patent Application
Publication No. 2009/0274609, which is incorporated herein by
reference in its entirety. The Raman spectra of SWNTs has three
major peaks, which are the G-band at about 1590 cm.sup.-1, D-band
at about 1350 cm.sup.-1, and the Radial breathing mode (RBM) at
about 100-300 cm.sup.-1. RBM frequency is proportional to an
inverse of the diameter of SWNTs and can thus be used to calculate
the diameter of the SWNT. Normally, a red shift in RBM peak
corresponds to an increase in the mean diameter of SWNTs. The
tangential mode G-band related to the Raman-allowed phonon mode
E.sub.2g can be a superposition of two peaks. The double peak at
about 1593 and 1568 cm.sup.-1 has been assigned to semiconductor
SWNTs, while the broad Breit-Wigner-Fano line at about 1550
cm.sup.-1 has been assigned to metallic SWNTs. Thus, G-band offers
a method for distinguishing between metallic and semiconducting
SWNTs. The D-band structure is related to disordered carbon, the
presence of amorphous carbon, and other defects due to the
sp.sup.2-carbon network. The ratio of the G-band to D-band in the
Raman spectra (I.sub.G:I.sub.D or G/D ratio) of SWNTs can be used
as an index to determine the purity and quality of the SWNTs
produced. Preferably, I.sub.G:I.sub.D is about 1 to about 500,
preferably about 5 to about 400, more preferably greater than about
7. Representative, non-limiting examples of Raman characterization
of carbon nanotubes synthesized according to the present disclosure
are shown in FIGS. 6 and 7. A representative, non-limiting example
of DTG of carbon nanotubes synthesized according to the present
disclosure is shown in FIG. 8.
[0036] As used herein, "co-depositing" of two or more substances
refers to the simultaneous deposition of two or more substances,
which were not previously in contact with one another.
Co-depositing may be carried out by any suitable means known to
those in the art, including but not limited to chemical vapor
deposition. Co-depositing may be carried out in a fume hood or with
other suitable apparatus, as will be known to those of ordinary
skill in the art. In some embodiments, the carbon nanotubes and the
electrode active material do not contact each other until they are
co-deposited onto the substrate.
[0037] Collecting the mixture of single-walled carbon nanotubes and
aerosolized electrode active material powder on a surface and
removing the carrier gas may be carried out by any suitable means.
The collecting surface of the porous substrate 40, 41 may be a
porous surface, including but not limited to a filter or a frit,
where the pores are appropriately sized to retain the mixture of
carbon nanotubes and the electrode active material thereon to form
the self-standing electrode while permitting passage of the carrier
and fluidizing gases. The carrier and fluidizing gases may be
removed after passing through the surface and by way of an outlet.
In some embodiments, removal of the carrier gas may be facilitated
by a vacuum source. With respect to filters, the filters may be in
the form of a sheet and may comprise a variety of different
materials including woven and non-woven fabrics. Illustrative
filter materials include, but are not limited to, cotton,
polyolefins, nylons, acrylics, polyesters, fiberglass, and
polytetrafluoroethylene (PTFE). To the extent the porous substrate
is sensitive to high temperatures, one or more of the streams 30A
and 30B may be precooled with dilution gases comprising a lower
temperature and/or by directing one or more of the streams 30A and
30B through a heat exchanger prior to contacting the movable porous
substrate.
[0038] As used herein, "fluidizing" refers to the conversion of a
granular material from a static-like solid state to a dynamic
fluid-like state, characterized by a tendency to flow. Fluidization
may be achieved by passing a fluid, such as a liquid or a gas, up
through the granular material, as will be known to those of
ordinary skill in the art. In some embodiments, fluidizing the
electrode active material comprises aerosolizing the electrode
active material.
[0039] In some embodiments, the aerosolizing of the electrode
active material comprises distributing an aerosolizing gas through
a first porous frit and a bed of an electrode active material, in
an aerosolizing chamber, to produce the aerosolized electrode
active material powder. The aerosolizing chamber may be constructed
with an appropriately sized porous material such that gas can pass
through to enable aerosolization but that does not permit the
active material to fall through the pores. The aerosolizing chamber
is not limited to any particular configuration. Suitable
aerosolizing gases include, but are not limited to, argon, helium,
or nitrogen. In some embodiments, the aerosolizing gas may be the
same as the carrier gas.
[0040] In some embodiments, the method further comprises
synthesizing the single-walled carbon nanotubes in a carbon
nanotube synthesis reactor. The reactor may comprise a catalyst or
catalyst precursor, a carbon source, one or more gas inlets, one or
more outlets, and a carbon nanotube growth zone. The one or more
gas inlets may be configured to let in one or more carrier
gases.
[0041] In some embodiments, the carbon nanotube synthesis reactor
may include a quartz tube of 25 mm OD.times.22 mm ID.times.760 mm
length and may be operated at atmospheric pressure. Alternatively,
the carbon nanotube synthesis reactor may be designed as described
in U.S. patent application Ser. No. 15/452,509, filed Mar. 7, 2017,
and Ser. No. 15/452,500, filed Mar. 7, 2017, both of which are
incorporated herein by reference. The carbon nanotube synthesis
reactor may be arranged at a variety of angles with respect to the
other equipment.
[0042] In some embodiments, the electrode active material is
selected from graphite, hard carbon, lithium metal oxides, lithium
iron phosphate, and metal oxides. In some embodiments, the
electrode active material for the anode may be graphite or hard
carbon. In some embodiments, the electrode active material for the
cathode may be lithium metal oxide or lithium iron phosphate.
[0043] Alternatively, the electrode active material may be selected
from electrode active materials described in U.S. patent
application Ser. No. 15/452,509, filed Mar. 7, 2017, and Ser. No.
15/452,500, filed Mar. 7, 2017, both of which are incorporated
herein by reference.
[0044] In a non-limiting example, the electrode active material may
be any solid, metal oxide powder that is capable of being
aerosolized. In an illustrative example, the metal oxide is a
material for use in the cathode of the battery. Non-limiting
examples of metal oxides include oxides of Ni, Mn, Co, Al, Mg, Ti
and any mixture thereof. The metal oxide may be lithiated. In an
illustrative example, the metal oxide is lithium nickel manganese
cobalt oxide (LiNiMnCoO.sub.2). The metal oxide powders can have a
particle size defined within a range between about 1 nanometer and
about 100 microns. In a non-limiting example, the metal oxide
particles have an average particle size of about 1 nanometer to
about 10 nanometers.
[0045] Metals in lithium metal oxides according to the present
disclosure may include but are not limited to one or more alkali
metals, alkaline earth metals, transition metals, aluminum, or
post-transition metals, and hydrates thereof. In some embodiments,
the electrode active material is lithium nickel manganese cobalt
oxide (LiNiMnCoO.sub.2).
[0046] "Alkali metals" are metals in Group I of the periodic table
of the elements, such as lithium, sodium, potassium, rubidium,
cesium, or francium.
[0047] "Alkaline earth metals" are metals in Group II of the
periodic table of the elements, such as beryllium, magnesium,
calcium, strontium, barium, or radium.
[0048] "Transition metals" are metals in the d-block of the
periodic table of the elements, including the lanthanide and
actinide series. Transition metals include, but are not limited to,
scandium, titanium, vanadium, chromium, manganese, iron, cobalt,
nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum,
technetium, ruthenium, rhodium, palladium, silver, cadmium,
lanthanum, cerium, praseodymium, neodymium, promethium, samarium,
europium, gadolinium, terbium, dysprosium, holmium, erbium,
thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium,
osmium, iridium, platinum, gold, mercury, actinium, thorium,
protactinium, uranium, neptunium, plutonium, americium, curium,
berkelium, californium, einsteinium, fermium, mendelevium,
nobelium, and lawrencium.
[0049] "Post-transition metals" include, but are not limited to,
aluminum, gallium, indium, tin, thallium, lead, bismuth, or
polonium.
[0050] In some embodiments, the method further comprises allowing
the mixture of single-walled carbon nanotubes and electrode active
material in the carrier gas to flow through one or more tubes
connecting the aerosolizing reactor, the carbon nanotube synthesis
reactor, and the collection chamber. In some embodiments, the one
or more tubes are at least about 0.5'' O.D. stainless tubing.
[0051] The loading or weight % of carbon nanotubes in the composite
self-standing electrode product is based on the relative amounts of
the nanotubes (or carbon source used to form the nanotubes) and the
electrode active material. It is within the level of ordinary skill
in the art to determine the relative starting amounts of carbon
source, catalyst/catalyst precursor, and electrode active material
that will afford a given loading or weight % of carbon nanotubes in
the composite self-standing electrode product. In a non-limiting
example, the self-standing electrode may comprise from 0.1% to 4%
by weight carbon nanotubes, and the balance the electrode active
material and optionally one or more additives. Optionally, the
self-standing electrode may comprise from 0.2% to 3% by weight
carbon nanotubes, and the balance the electrode active material and
optionally one or more additives. Optionally, the self-standing
electrode may comprise from 0.75% to 2% by weight carbon nanotubes,
and the balance the electrode active material and optionally one or
more additives. Additives and/or dopants may be present for each
range in an amount of 0 to 5% by weight. In a non-limiting example,
the self-standing electrode consists essentially of the carbon
nanotubes and the electrode active material powder. In a
non-limiting example, the self-standing electrode consists of the
carbon nanotubes and the electrode active material powder. For each
of the ranges, the self-standing electrode may be free of any
binders. The lack of a binder results in a self-standing electrode
with improved flexibility. Further, it has been discovered that a
higher carbon nanotube content increases the flexibility of the
self-standing electrode. Without being bound to any particular
theory, this is likely due to the webbed morphology of the
self-standing electrode in which there is a webbed arrangement of
carbon nanotubes with the electrode active material contained or
embedded within the web.
[0052] In a non-limiting example, the self-standing electrode may
comprise a density of 0.9 to 1.75 g/cc. Optionally, the
self-standing electrode may comprise a density of 0.95 to 1.25
g/cc. Optionally, the self-standing electrode may comprise a
density of 0.75 to 2.0 g/cc. Optionally, the self-standing
electrode may comprise a density of 0.95 to 1.60 g/cc.
[0053] In a non-limiting example, the self-standing electrode may
comprise a thickness of up to 750 .mu.m following collection on the
porous substrate. Optionally, the self-standing electrode may
comprise a thickness of 50 .mu.m to 500 .mu.m following collection
on the porous substrate. Optionally, the self-standing electrode
may comprise a thickness of from 100 .mu.m to 450 .mu.m following
collection on the porous substrate. Optionally, the self-standing
electrode may comprise a thickness of from 175 .mu.m to 250 .mu.m
following collection on the porous substrate.
[0054] In some embodiments, the method of the present disclosure
may further comprise treating the composite or self-standing
electrode, including but not limited to pressing the composite or
self-standing electrode. Without wishing to be bound to any
particular theory, pressing may increase the density and/or lower
the thickness of the self-standing electrode, which may improve
such properties as rate performance, energy density, and battery
life. Pressing of the self-standing electrodes may be carried out
by applying a force to achieve a desired thickness and/or density,
such as by using a rolling press or calendaring machine, platen
press, or other suitable means, as will be known to those of
ordinary skill in the art. Any suitable force may be applied, to
achieve a desired thickness, and/or density, and/or impedance, such
as but not limited to a force of about 1 ton, about 2 tons, about 3
tons, about 4 tons, about 5 tons, about 6 tons, about 7 tons, about
8 tons, about 9 tons, about 10 tons, about 15 tons, or any integer
or range in between, such as between about 7 tons and about 10
tons. In some embodiments, pressing may be limited to pressing to a
thickness of about 20 microns, about 30 microns, about 40 microns,
about 50 microns, about 60 microns, about 70 microns, about 80
microns, about 90 microns, about 100 microns, about 150 microns,
about 200 microns, about 250 microns, about 300 microns, about 350
microns, about 400 microns, or any integer or range in between.
Without wishing to be bound by any particular theory, too thick of
an electrode may be slow to produce energy or may not be suitably
flexible. In some embodiments, it may be desirable to obtain an
electrode foil that is flexible without formation of oxide or
cracks. If the electrode is too thin, energy production may be
rapid but it may be the case that not enough energy is produced. In
addition, it may be desirable to regulate the distance between the
rolls or rollers in a rolling press or calendaring machine, or
between the plates of a platen press, by any suitable means known
to those of ordinary skill in the art.
[0055] Determination of a suitable amount of pressing is within the
level of ordinary skill in the art. As will be known to those of
ordinary skill in the art, excessive pressing may cause the
electrolyte to penetrate the electrode too much, as determined by
measuring impedance and/or resistance to diffusion. As will be
evident to those of ordinary skill in the art, it may be of
interest to minimize the electrolyte diffusion resistance or
coefficient for a given electrolyte, as measured by impedance. In a
non-limiting example, the thickness of the self-standing electrode
following pressing may be from 40% to 75% of the thickness of the
untreated self-standing electrode, or the self-standing electrode
following collection on the porous substrate. Optionally, the
thickness of the self-standing electrode following pressing may be
from 45% to 60% of the thickness of the untreated self-standing
electrode, or the self-standing electrode following collection on
the porous substrate.
[0056] In a non-limiting example, the density of the self-standing
electrode following pressing is increased by 40% to 125% of the
density of the untreated self-standing electrode, or the
self-standing electrode following collection on the porous
substrate. Optionally, the density of the self-standing electrode
following pressing is increased by 45% to 90% of the density of the
untreated self-standing electrode, or the self-standing electrode
following collection on the porous substrate.
[0057] Electrodes pressed to thinner thicknesses may be unsuitably
brittle. Non-limiting examples of electrode thickness and density,
with and without pressing, are shown in the table below:
TABLE-US-00001 Single- walled nanotube Thickness loading Original
Original after Pressed (weight thickness density pressing density
Sample No. Weight (mg) %) (.mu.m) (g/cc) (mm) (g/cc) 1 417 1.2 125
1.20 unknown unknown 2 612 1.1 200 1.11 unknown unknown 3 572 1.1
200 1.03 unknown unknown 4 318 1.9 unknown unknown unknown unknown
5 138 1.5 unknown unknown unknown unknown 6 151 1.6 unknown unknown
unknown unknown 7 293 0.46 196 1.25 112 2.14 8 265 0.73 211 1.05
148 1.49 9 339 0.41 244 1.16 128 2.20 10 811 0.21 434 1.56 220 2.28
11 266 0.63 231 0.96 109 2.03
[0058] In some embodiments, the fluidizing of the electrode active
material comprises distributing an aerosolizing gas through,
sequentially, a porous frit and a bed of the electrode active
material, in an active material container, to form an aerosolized
electrode active material. The pores of the porous frit may be
sized to permit passage of the aerosolizing gas through to enable
aerosolization but not permit the active material to fall through
the pores. The active material container may be any container
capable of fluidizing, such as aerosolizing, the electrode active
material, including but not limited to a modified gas washing
bottle. Aerosolizing gases suitable for use with the present
disclosure include but are not limited to an inert gas, such as
argon gas or helium gas; hydrogen gas; nitrogen gas; or a
combination thereof. In some embodiments, the aerosolizing gas is
the same as the carrier gas.
[0059] In some embodiments, the present disclosure is directed to
an apparatus for producing a self-standing electrode, the apparatus
comprising a carbon nanotube synthesis reactor configured to
synthesize carbon nanotubes; an active material container
configured to fluidize an electrode active material; a movable
porous flexible substrate configured to collect the carbon
nanotubes and the fluidized electrode active material to form the
self-standing electrode comprising a composite of the carbon
nanotubes and the electrode active material. All embodiments
described for the method apply to the apparatus with equal force,
and vice versa.
[0060] In some embodiments, the carbon nanotube synthesis reactor
comprises one or more gas inlets, one or more gas outlets, and a
carbon nanotube growth zone where a catalyst or catalyst precursor
and a carbon source are used to grow the carbon nanotubes.
[0061] In some embodiments, the active material container comprises
a porous frit; and a vertical shaker. The active material container
may further contain one or more gas Inlets and one or more gas
outlets, and the one or more gas inlets may be configured to take
in one or more fluidizing gases, such as one or more aerosolizing
gases.
[0062] In some embodiments, the movable porous flexible substrate
is connected to a roll-to-roll system.
[0063] In some embodiments, the present disclosure is directed to a
self-standing electrode, comprising a composite of an electrode
active material and single-walled carbon nanotubes; wherein the
self-standing electrode does not contain binder material or a
metal-based current collector material.
[0064] In some embodiments, the electrode is characterized by a
webbed morphology or a net. In some embodiments, a webbed
morphology or a net is a webbed arrangement of carbon nanotubes
with the electrode active material contained or embedded within the
carbon nanotube web or net.
[0065] Composites or self-standing electrodes prepared according to
the present disclosure may be of any desired thickness and may be
cut according to requirements. Thickness may be controlled by
factors including, but not limited to, the rate of motion of the
movable substrate, the rate of deposition of the carbon nanotubes
and/or the electrode active material, and the carbon nanotube
loading (weight %).
[0066] While the aspects described herein have been described in
conjunction with the example aspects outlined above, various
alternatives, modifications, variations, improvements, and/or
substantial equivalents, whether known or that are or may be
presently unforeseen, may become apparent to those having at least
ordinary skill in the art. Accordingly, the example aspects, as set
forth above, are intended to be illustrative, not limiting. Various
changes may be made without departing from the spirit and scope of
the disclosure. Therefore, the disclosure is intended to embrace
all known or later-developed alternatives, modifications,
variations, improvements, and/or substantial equivalents.
[0067] Thus, the claims are not intended to be limited to the
aspects shown herein, but are to be accorded the full scope
consistent with the language of the claims, wherein reference to an
element in the singular is not intended to mean "one and only one"
unless specifically so stated, but rather "one or more." All
structural and functional equivalents to the elements of the
various aspects described throughout this disclosure that are known
or later come to be known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the claims. Moreover, nothing disclosed herein is
intended to be dedicated to the public regardless of whether such
disclosure is explicitly recited in the claims. No claim element is
to be construed as a means plus function unless the element is
expressly recited using the phrase "means for."
[0068] Further, the word "example" is used herein to mean "serving
as an example, instance, or illustration." Any aspect described
herein as "example" is not necessarily to be construed as preferred
or advantageous over other aspects. Unless specifically stated
otherwise, the term "some" refers to one or more. Combinations such
as "at least one of A, B, or C," "at least one of A, B, and C," and
"A, B, C, or any combination thereof" include any combination of A,
B, and/or C, and may include multiples of A, multiples of B, or
multiples of C. Specifically, combinations such as "at least one of
A, B, or C," "at least one of A, B, and C," and "A, B, C, or any
combination thereof" may be A only, B only, C only, A and B, A and
C, B and C, or A and B and C, where any such combinations may
contain one or more member or members of A, B, or C. Nothing
disclosed herein is intended to be dedicated to the public
regardless of whether such disclosure is explicitly recited in the
claims.
[0069] Moreover, all references throughout this application, for
example patent documents including issued or granted patents or
equivalents; patent application publications; and non-patent
literature documents or other source material; are hereby
incorporated by reference herein in their entireties, as though
individually incorporated by reference.
* * * * *