U.S. patent application number 16/821144 was filed with the patent office on 2020-07-16 for carbonaceous composite materials with snowball-like morphology.
The applicant listed for this patent is ImerTech SAS. Invention is credited to Sergio PACHECO BENITO, Michael SPAHR, Hiroyuki TAKI, Pirmin ULMANN, Simone ZURCHER.
Application Number | 20200227747 16/821144 |
Document ID | 20200227747 / US20200227747 |
Family ID | 54360010 |
Filed Date | 2020-07-16 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200227747 |
Kind Code |
A1 |
SPAHR; Michael ; et
al. |
July 16, 2020 |
CARBONACEOUS COMPOSITE MATERIALS WITH SNOWBALL-LIKE MORPHOLOGY
Abstract
The present disclosure relates to a novel process for preparing
isotropic carbonaceous composite particles with favorable
crystallographic, morphological & mechanical properties,
wherein relatively fine carbonaceous primary particles are coated
with a carbonaceous binder precursor material, agglomerated and
finally heat-treated at temperatures between about 1850 and
3500.degree. C. to convert the binder precursor material to
non-graphitic or graphitic carbon, thereby resulting in stable
highly isotropic carbonaceous composite materials wherein the
primary particles of the aggregate are held together by the
carbonized/graphitized binder. The present disclosure also relates
to the isotropic carbonaceous composite particles obtainable by the
process described herein. The disclosure further relates to uses of
said isotropic carbonaceous composite material in various
applications, including as active material in negative electrodes
in lithium-ion batteries, and in secondary products containing said
isotropic carbonaceous composite material.
Inventors: |
SPAHR; Michael;
(Bellinozona, CH) ; ULMANN; Pirmin; (Giubiasco,
CH) ; ZURCHER; Simone; (Origlio, CH) ; PACHECO
BENITO; Sergio; (Biasca, CH) ; TAKI; Hiroyuki;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ImerTech SAS |
Paris |
|
FR |
|
|
Family ID: |
54360010 |
Appl. No.: |
16/821144 |
Filed: |
March 17, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15735970 |
Dec 13, 2017 |
10637058 |
|
|
PCT/EP2016/075423 |
Oct 21, 2016 |
|
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16821144 |
|
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62244556 |
Oct 21, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/366 20130101;
H01M 4/587 20130101; H01M 2220/20 20130101; C01B 32/05 20170801;
Y02E 60/10 20130101; H01M 10/054 20130101; C01P 2004/51 20130101;
Y02P 70/54 20151101; Y02T 10/7011 20130101; Y02E 60/122 20130101;
Y02P 70/50 20151101; C01B 32/205 20170801; Y02T 10/70 20130101;
C01B 32/00 20170801; H01M 2004/027 20130101; H01M 10/446 20130101;
H01M 10/0525 20130101; C01P 2006/12 20130101; H01M 4/364 20130101;
H01M 2/00 20130101 |
International
Class: |
H01M 4/587 20060101
H01M004/587; H01M 10/0525 20060101 H01M010/0525; H01M 10/054
20060101 H01M010/054; H01M 10/44 20060101 H01M010/44; H01M 4/36
20060101 H01M004/36; C01B 32/00 20060101 C01B032/00; H01M 2/00
20060101 H01M002/00; C01B 32/205 20060101 C01B032/205; C01B 32/05
20060101 C01B032/05 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2015 |
EP |
15190921.5 |
Claims
1-73. (canceled)
74. A process for preparing carbonaceous composite particles,
comprising: (a) attaching a carbonaceous binder precursor material
to the surface of carbonaceous particles in the presence of a
solvent, thereby forming a coating of the carbonaceous particles by
the carbonaceous binder precursor material; (b) drying the material
obtained from step (a); and (c) during or after step (a) or step
(b), causing agglomeration of the coated primary carbonaceous
particles.
75. The process according to claim 74, wherein the carbonaceous
composite particles are comprised of a multiplicity of aggregated
primary particles, wherein said primary particles are held together
by a carbonaceous binder material attached to the surface of the
primary particles.
76. The process of claim 74, wherein the carbonaceous binder
precursor material is not or does not include ammonium
lignosulfonate, and is not or does not include coal tar, tar pitch,
and petroleum pitch.
77. The process according to claim 74, wherein the carbonaceous
particles employed in step (a) are selected from the group
consisting of natural graphite, synthetic graphite, graphene,
graphene nanoplatelets, graphene or carbon fibers, fullerenes,
nanographite, hard carbon, soft carbon, petroleum- or coal-based
coke, graphitized fine coke, char, carbon black, carbon nanotubes
(CNT), including single-walled nanotubes (SWNT), multiwalled
nanotubes (MWNT), carbon nanofibers (CNF) or mixtures thereof; or
from non-carbonaceous materials such as silicon, silicon oxide,
tin, tin oxide or tin dioxide, aluminum, bismuth, lithium titanate,
or mixtures of any of the foregoing.
78. The process according to claim 74, wherein the carbonaceous
particles employed in step (a) are non-graphitic particles.
79. The process according to claim 74, wherein the particle size
distribution of said carbonaceous particles employed in step (a) is
characterized by at least one of: i) a D90 of <35 .mu.m, ii) a
D50 of <about 20 .mu.m, iii) a D90 of <25 .mu.m, and iv) a
D50 of <about 15 .mu.m; (v) a sphericity Q3 [S=0.8] of equal or
more than about 22%; and (vi) a Scott density of >0.2 g/cm3.
80. The process according to claim 74, wherein the carbonaceous
binder precursor material to be used in step (a) is selected from
the group consisting of polymers such as a lignin-based polymer, a
polystyrene or derivative thereof, styrene-butadiene, melted phenol
resin, polyvinylalcohol, polyfurfuryl alcohol, furfural,
polyurethane, polystyrene-acrylate, polyacrylate,
polymethylmethacrylate, polymethacrylonitrile, polyoxymethylene,
poly(methyl atropate), polyisobutene, polyethyleneoxide,
polypropyleneoxide, polyethylene, polypropylene,
polymethylacrylate, polybutadiene, polyisoprene, polyacrylonitrile,
polyaniline, tannic acid, starch, gum arabic, maltodextrin,
formaldehyde phenol resins, formaldehyde tetrahydrofuran resins,
nitrile butyl rubber, sucrose, glucose, or other sugars, polyethyl
ether ketone, polyphenylene sulfide, polyvinyl chloride,
carboxymethylcellulose, methyl cellulose, gelatins, polyvinyl
pyrrolidone, polylactic acid, latexes thereof, a hydrocarbon gas
such as methane, ethane, ethylene, propane, propene, acetylene,
butane, benzene, toluene, xylene, or an alcohol such as ethanol,
propanol, isopropanol, mixed with an inert carrier gas, and
combinations thereof.
81. The process according to claim 74, wherein the attachment of
the carbonaceous binder precursor material to the surface of the
carbonaceous particles is achieved by a method selected from the
group consisting of: i) mixing to form a dispersion, optionally in
the presence of a solvent and subsequent drying; ii) melting the
carbonaceous binder precursor onto the primary particles; (iii)
pyrolysis; (iv) pitch-coating; and (v) evaporation.
82. The process according to claim 74, wherein the agglomeration of
step (c) is achieved by spray-drying a dispersion comprising the
primary carbonaceous particles and the carbonaceous binder
precursor material.
83. The process according to claim 74, wherein the drying of step
(b) and the agglomeration of step (c) is achieved by at least one
of: spray-drying a dispersion comprising the primary carbonaceous
particles and the carbonaceous binder precursor material obtained
from step (a) in a spray dryer; vacuum-drying a dispersion
comprising the primary carbonaceous particles and the carbonaceous
binder precursor material obtained from step (a) in a heatable
vacuum reactor; freeze-drying a dispersion comprising the primary
carbonaceous particles and the carbonaceous binder precursor
material obtained from step (a) in a stirred freeze dryer;
flash-drying a dispersion comprising the primary carbonaceous
particles and the carbonaceous binder precursor material obtained
from step (a) in a flash dryer; drying a fluidized dispersion
comprising the primary carbonaceous particles and the carbonaceous
binder precursor material obtained from step (a) in a fluidized bed
dryer, optionally in combination with a spray system; disc drying a
dispersion comprising the primary carbonaceous particles and the
carbonaceous binder precursor material obtained from step (a) in a
disc dryer; and paddle drying a dispersion comprising the primary
carbonaceous particles and the carbonaceous binder precursor
material obtained from step (a) in a paddle dryer.
84. The process according to claim 74 further comprising: (d)
carbonizing said carbonaceous binder precursor material attached to
the surface of the agglomerated particles from step (c) by a
thermal decomposition under vacuum or an inert atmosphereat
temperatures ranging from 400.degree. C. to 3500.degree. C.
85. The process according to claim 84, wherein prior to the
carbonizing of step (d), the coated agglomerated carbonaceous
particles are subjected to a pre-treatment performed under vacuum,
air, nitrogen, argon or CO.sub.2 atmosphere at temperatures of
below 1000.degree. C.
86. The process according to claim 84, wherein the particles
obtained from step (d) are subjected to an additional heat
treatment in a gas atmosphere selected from one of: nitrogen,
argon, mixtures of nitrogen with hydrocarbons like acetylene,
propane or methane, or with oxidative gases such as air, steam, or
CO.sub.2 to adjust the morphology and surface chemistry of the
carbonaceous composite particles.
87. The process according to claim 84, wherein the particles
obtained from step (d) are subjected to an additional heat
treatment performed by contacting the particles with an oxidant
either in a gaseous/solid phase process with air, carbon dioxide,
water vapor, oxygen, ozone, or any combination thereof, or,
alternatively, in a liquid/solid phase process with aqueous
hydrogen peroxide or other oxidants present in said liquid
phase.
88. A process for preparing carbonaceous composite particles,
comprising: (a) attaching a carbonaceous binder precursor material
to the surface of carbonaceous particles thereby forming a coating
of the carbonaceous particles by the carbonaceous binder precursor
material; and (b) during or after step (a), causing agglomeration
of the coated primary carbonaceous particles.
89. The process according to claim 88, wherein the particle size
distribution of said carbonaceous particles employed in step (a) is
characterized by at least one of: i) a D90 of <35 .mu.m, ii) a
D50 of <about 20 .mu.m, iii) a D90 of <25 .mu.m, and iv) a
D50 of <about 15 .mu.m; (v) a sphericity Q3 [S=0.8] of equal or
more than about 22%; and (vi) a Scott density of >0.2 g/cm3.
90. The process according to claim 88, wherein the agglomeration of
step (b) is achieved by spray-drying a dispersion comprising the
primary carbonaceous particles and the carbonaceous binder
precursor material.
91. The process according to claim 88 further comprising: (c)
carbonizing said carbonaceous binder precursor material attached to
the surface of the agglomerated particles from step (b) by a
thermal decomposition under vacuum or an inert atmosphere at
temperatures ranging from 400.degree. C. to 3500.degree. C.
92. The process according to claim 91, wherein prior to the
carbonizing of step (c), the coated agglomerated carbonaceous
particles are subjected to a pre-treatment performed under vacuum,
air, nitrogen, argon or CO.sub.2 atmosphere at temperatures of
below 1000.degree. C.
93. The process according to claim 91, wherein the particles
obtained from step (c) are subjected to an additional heat
treatment by one of: i) heating the particles in a gas atmosphere
selected from one of: nitrogen, argon, mixtures of nitrogen with
hydrocarbons like acetylene, propane or methane, or with oxidative
gases such as air, steam, or CO.sub.2 to adjust the morphology and
surface chemistry of the carbonaceous composite particles; ii)
heating the particles in the presence of an oxidant in a
gaseous/solid phase process with air, carbon dioxide, water vapor,
oxygen, ozone, or any combination thereof; and iii) heating the
particles in the presence of an oxidant in a liquid/solid phase
process with aqueous hydrogen peroxide or other oxidants present in
said liquid phase.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates to a novel process for
preparing isotropic carbonaceous composite particles with favorable
crystallographic and morphological properties, as well as to the
isotropic carbonaceous composite particles obtainable by said
process. The disclosure also relates to the uses of said isotropic
carbonaceous composite material in various applications, including
as active material in negative electrodes of lithium-ion batteries,
and other products containing said isotropic carbonaceous composite
material.
BACKGROUND OF THE DISCLOSURE
[0002] Lithium-ion batteries are widely used in portable consumer
devices like portable computers, mobile phones, and video or
photographic cameras. In addition, large-scale lithium batteries
are an attractive battery technology for hybrid electric vehicles,
plug-in electric vehicles, and fully electric vehicles that will
have a growing future market share due to their improved fuel
economy and lowered CO.sub.2 gas emission. The growing importance
of renewable energy production requires large energy storage
systems and large-scale lithium-ion batteries are considered as
potential battery systems used in smart grids to compensate peak
power consumption in houses or to store the energy produced in
off-grid photovoltaic systems.
[0003] Graphite is used as the electrochemically active material in
the negative electrode of lithium-ion batteries. The graphite
crystallinity is required to obtain high reversible specific
charges (reversible electrochemical capacity) up to a theoretical
value of 372 Ah/kg of graphite. The electrochemical redox process
generating the energy is based on the reversible electrochemical
intercalation of lithium into the graphite structure. The
theoretical reversible capacity corresponds to a stoichiometry of
LiC.sub.6 of the stage-1 lithium-graphite intercalation compound
formed in this intercalation process. During the charging process
of the lithium-ion cell, lithium ions from the positive electrode
containing materials such as LiCo.sub.xNi.sub.yMn.sub.zO.sub.2
where x+y+z=1 and having a layered structure, the LiMn.sub.2O.sub.4
with spinel structure, or LiFePO.sub.4 of olivine-type migrate
through the electrolyte and are intercalated in the graphite
negative electrode. During the discharge process, the lithium ions
are deintercalated from the graphite and inserted in the structure
of the positive electrode material.
[0004] Details about the lithium-ion battery technology and
carbonaceous negative electrode materials are described in several
reviews and monographs (see for example: P. Novak, D. Goers, M. E.
Spahr, "Carbon Materials in Lithium-Ion Batteries", in: Carbons for
Electrochemical Energy Storage and Conversion Systems, F. Beguin,
E. Frackowiak (Eds.), Chapter 7, p. 263-328, CRC Press, Boca Raton
FI, USA, 2010; Lithium-Ion Batteries-Science and Technologies, M.
Yoshio, R. J. Brodd, A. Kozawa (Eds.), Springer, New York, N.Y.,
2009; Lithium Batteries-Science and Technology, G.-A. Nazri, G.
Pistoia (Eds.), Kluwer Academic Publishers, Norwell, Mass., USA,
2004; Carbon Anodes for Lithium-Ion Batteries, in: New Carbon Based
Materials for Electrochemical Energy Storage Systems, I. Barsukov,
C. S. Johnson, J. E. Doninger, W. Z. Barsukov (Eds.), Chapter 3,
Springer, Dordrecht, The Netherlands, 2006).
[0005] Similarly, isotropic carbon materials are also advantageous
for graphite bipolar plates in PEM fuel cells. Bipolar plates in
fuel cells are normally plagued by the low through-plane
conductivity when flaky additives are used. A material with a
higher isotropy improves the through-plane conductivity of the
bipolar plate.
[0006] Furthermore, isotropic carbon materials are beneficial in
current collector coatings for various battery systems in order to
achieve a high through-plane conductivity.
State of the Art in Graphite Particle Shaping and Coating
[0007] The rounding of platelet-like graphite particles can be
achieved by special mechanical treatments, typically of natural
graphite, in ball mills, hammer mills, or by an autogenous grinding
process. Usually, in these processes a large amount of fines or
graphite dust is created that has to be separated from the rounded
graphite product, causing a significant loss of graphite. In
addition, the rounding of particle contours does not significantly
change the anisotropic arrangement of the crystallites contained in
the particles and introduces strain into the particles that can
lead to swelling effects in lithium-ion batteries when this strain
is released during cycling.
[0008] The coating of the graphite particles by an amorphous carbon
layer at present is achieved in the industry mostly by mixing the
graphite particles with coal tar pitch either in a mixing process
in which the pitch is mixed either as dry powder, molten liquid, or
dissolved in an organic solvent. Subsequently the dry
graphite/pitch mixture is carbonized and subsequently calcined
under inert gas conditions at temperatures around 1500.degree. C.
One major problem of this coating process is the impact of coal tar
pitch or other pitch types on the environment and health as some of
the polyaromatic organic pitch ingredients ("PAHs") are considered
highly toxic, carcinogenic, and/or mutagenic. Therefore, coal tar
pitch is considered as a substance of very high concern in the
European REACH regulation and requires a controlled use in existing
manufacturing processes. New permissions for production processes
involving coal tar pitch are usually not granted by state
authorities in Europe. Newly developed production processes
therefore require alternatives to pitch-based coating processes
that so far do not appear to exist. Pitch alternatives like special
polymers or other solid organic substances that result in high
carbon yield during carbonization are significantly more expensive,
may not lead to the same quality of carbon coating, or are of
environmental or health concern as well.
[0009] Graphitized mesocarbon microbeads (MCMB) stands for an
artificial graphitic coke with spherical particle shape. When
heating coal tar pitch at about 450.degree. C. solid spherical coke
particles are formed in the melt. The spherical particles are
extracted, oxidized at elevated temperatures in air, carbonized and
finally graphitized, resulting in particles with a smooth spherical
surface.
[0010] Fast charge and discharge performance is of key importance
for lithium-ion batteries in several applications. Specifically,
automotive lithium-ion batteries used in fully electric vehicles or
in plug-in electric vehicles require high capacity graphite-based
active materials in the negative electrode. The alignment of the
anisotropic graphite platelets along the platelet planes in the
electrode and the electrode pore structure is considered to be
responsible for the limited lithium-ion diffusion in the porous
graphite electrode. The limitations with regard to lithium-ion
diffusion and solid state diffusion of lithium are often seen as a
reason for the non-ideal performance characteristics of graphite
electrodes at high current rates during charge and discharge. The
diffusion limitation of such graphite electrodes do not only reduce
the cell power and charging speed, but may also cause the plating
of metallic lithium at the negative electrode surface during the
charging of the cell at high current rates, which is considered as
a major safety problem of lithium-ion batteries.
[0011] In commercial graphite negative electrode materials based on
natural graphite, the platelet-like shape of graphite is often
modified to a more spherical or rounded shape. Rounded carbon
particle shape is normally achieved by special mechanical
treatments. The mechanical treatments abrade the edges thereby
rounding the particles and as a consequence increasing the fine
fraction in the particle size distribution and creating create many
surface defects that can lead to parasitic reactions in lithium-ion
batteries. However, these mechanical treatments do not
significantly change the anisotropic particle character, i.e.
resulting particles may show rounded particle contours, but do not
avoid the problems described above.
[0012] Isotropic hard carbons have historically been used due to
their favorable lithium intercalation/de-intercalation curves for
applications in which fast charge and discharge and low temperature
performance is important. The reversible capacity of these hard
carbons is, however, lower than for graphite.
[0013] The importance of an isotropic pore shape and low tortuosity
has been demonstrated in positive electrodes, see D. E. Stephenson
et al. J. Electrochem. Soc. 2011, 158 (7), A781.
[0014] Isotropic graphite particles can be made by agglomeration of
smaller particles in a random or at least near random orientation.
However, a problem with many agglomerated graphite particles is the
inherent fragility of the particle morphology since these
agglomerates are typically only held together by adhesion (mainly
through van der Waals forces), which facilitates the integrity of
the coating (if present) and their break-up into smaller particles,
thereby resulting in a higher surface area. This instability is
particularly relevant for material that undergoes mechanical
treatments for example upon pressing the graphite material into a
negative electrode of a lithium-ion battery. It is readily apparent
that the breakage of assembled particles is problematic, not the
least in view of the change of the particle characteristics.
[0015] Thus, it would be desirable to produce carbonaceous
materials that allow producing electrodes exhibiting on the one
hand desirable fast charge and discharge characteristics, high
reversible capacity, and/or exhibiting mechanical stability,
allowing the particles to maintain their morphology and surface
properties, for example during the pressing process for preparing
the electrodes.
SUMMARY OF THE DISCLOSURE
[0016] The present inventors have developed a novel process to
produce highly isotropic carbonaceous particles that do not exhibit
the problems observed with assembled graphite materials of the
prior art, i.e. they may be characterized by an isotropic
morphology and high porosity favorable for fast charge and
discharge capability, high reversible capacity and excellent
mechanical stability.
[0017] Thus, in a first aspect the present disclosure relates to
carbonaceous composite particles, wherein said particles are
comprised of a multiplicity of aggregated primary particles, and
wherein said primary particles are held together by a carbonaceous
binder material attached to the surface of the primary particles.
These composite particles are further characterized by any one or a
combination of the following parameters:
(i) a pressure stability, wherein the BET specific surface area
does not increase by more than 3.5 m.sup.2/g; and/or by not more
than 80% (compared to the BET specific surface area of the
particles before pressing) after pressing at 15 kN/cm.sup.2 for 10
s; (ii) a mass loss of non-graphitic carbon according to
thermogravimetric analysis of less than 5%, or less than 2%, or
less than 1%, or less than 0.5%; and/or (iii) by having a
crystalline surface with a surface crystallinity expressed by an
L.sub.a of >4 nm, or >6 nm, or >10 nm, as determined by
measuring the I.sub.D/I.sub.G band amplitude ratio via Raman
spectroscopy.
[0018] Another aspect of the present disclosure relates to
compositions comprising the carbonaceous composite particles as
defined herein. These compositions may comprise one type of
carbonaceous composite particles or may comprise different types of
the carbonaceous composite particles as described herein.
[0019] Yet another aspect relates to a process for making such
carbonaceous composite particles. The process as described herein
comprises attaching a carbonaceous binder precursor material to the
surface of carbonaceous particles, optionally in the presence of a
solvent, thereby forming a coating of the (primary) carbonaceous
particles by the carbonaceous binder precursor material. If a
solvent was used in this step, the dispersion is dried to remove
any solvent. During or after the coating and/or the drying step,
the process further comprises causing agglomeration of the coated
primary carbonaceous particles. After agglomeration, the dry
agglomerated particles are subjected to a high temperature
treatment between about 1850 and 3500.degree. C. This heat
treatment yields carbonaceous composite particles comprised of a
multiplicity of aggregated primary particles, wherein said primary
particles are held together by a carbonaceous binder material
attached to the surface of the primary particles. In other words,
the primary particles are "glued" together by the carbonaceous
binder precursor material which is converted to carbon or even
graphite during the heat treatment at temperatures above
1850.degree. C. (practically up to 3500.degree. C., though at some
point economic considerations prevent a heating above such
temperatures).
[0020] Yet another aspect relates to the use of the carbonaceous
composite particles or the compositions as described herein for
preparing a negative electrode material for a lithium-ion battery.
Consequently, a negative electrode of a lithium-ion battery
comprising the carbonaceous composite particles as described herein
as an active material in the negative electrode of the battery is
another aspect of the present disclosure, as is a lithium-ion
battery comprising said carbonaceous composite particles.
[0021] A further aspect relates to an energy storage device, a
carbon brush, a polymer composite material comprising the
carbonaceous composite particles or the composition comprising said
carbonaceous composite particles as described herein.
[0022] Yet a further aspect relates to an electric vehicle, hybrid
electric vehicle, or plug-in hybrid electric vehicle comprising a
lithium-ion battery with favorable fast charge and discharge as
well as low temperature performance properties, wherein said
lithium-ion battery comprises the carbonaceous composite particles
or the composition comprising said carbonaceous composite particles
as described herein as an active material in the negative electrode
of the battery.
[0023] Yet another aspect relates to a sodium-ion battery
comprising the carbonaceous composite particles or the composition
comprising said carbonaceous composite particles as described
herein.
[0024] Another aspect of the present disclosure relates to a
carbon-based coating exhibiting isotropic electric, mechanical or
heat-conducting properties, wherein said coating comprises the
carbonaceous composite particles or the composition comprising said
carbonaceous composite particles as described herein, as well as to
the use of said carbon-based coating as a coating of a current
collector in batteries.
[0025] A dispersion comprising the carbonaceous composite particles
or the composition comprising said carbonaceous composite particles
as described herein is another aspect of the present
disclosure.
[0026] Finally, the present disclosure also relates to a method for
making a building block of a negative electrode, employing the
carbonaceous composite particles or the composition comprising said
carbonaceous composite particles as described herein.
BRIEF DESCRIPTION OF THE FIGURES
[0027] FIG. 1, panel a) shows a scanning electron microscope (SEM)
image of graphitic carbon powder 4 prepared as described in Example
1. Panel b) is a magnification of a single spherical particle.
[0028] FIG. 2, panel a) shows a scanning electron microscope (SEM)
image of carbon intermediate 5 prepared as described in Example 2.
Panel b) is a magnification of a single spherical particle showing
the presence of non-crystalline binder droplets on the surface.
[0029] FIG. 3, panel a) shows a scanning electron microscope (SEM)
image of a graphitic carbon powder 6 prepared as described in
Example 2. Panel b) is a magnification of a single spherical
particle.
[0030] FIG. 4, panel a) shows a scanning electron microscope (SEM)
image of carbon powder 7 prepared as described in Example 3. Panel
b) is a magnification of a single spherical particle.
[0031] FIG. 5 shows scanning electron microscope (SEM) images of
cross-sections of unpressed electrodes containing the active carbon
mixture 13, at three different magnifications.
[0032] FIG. 6 shows scanning electron microscope (SEM) images of
cross-sections of pressed electrodes containing the active carbon
mixture 13, at three different magnifications.
[0033] FIG. 7 shows the Log differential intrusion against the pore
size for synthetic graphite, natural graphite and carbon powder 11
as measured by mercury porosimetry.
[0034] FIG. 8 shows the cumulative intrusion against the pore size
for synthetic graphite, natural graphite and carbon powder 11 as
measured by mercury porosimetry.
[0035] FIG. 9 shows the incremental pore volume against the
pressure for synthetic graphite, natural graphite and carbon powder
11 as measured by mercury porosimetry.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0036] The relevant disclosures in the prior art documents
mentioned herein are hereby incorporated by reference in their
entirety. All terms used in the present application shall have the
meaning usually employed by a relevant person skilled in the art,
unless specifically defined otherwise in this disclosure.
[0037] A novel multistep-process has been developed by the present
inventors which allows the generation of novel highly isotropic
carbonaceous (i.e. graphitic or non-graphitic) composite particles
that may exhibit excellent mechanical and electrochemical
properties. More specifically, the process is suitable to produce
highly spherical particles with a large content of
electrolyte-accessible pores or channels (i.e., high electrolyte
diffusion capacity) in combination with relatively high xylene
densities (such as above 2.20 g/cm.sup.3). This morphology is
beneficial for producing electrodes exhibiting favorable lithium
diffusion and electrochemical capacities, leading to cells with
high energy, power density and charging speed.
[0038] These advantageous properties render the novel carbonaceous
composite particles very useful as an active material of negative
electrodes in lithium-ion batteries, particularly for applications
where fast charge and discharge as well as low temperature
performance is required. For example, automotive lithium-ion
batteries used in fully electric vehicles or in plug-in electric
vehicles require high capacity graphite-based active materials in
the negative electrode that allow the manufacture of electrodes
with electrolyte filled channels exhibiting low tortuosity,
allowing the lithium-ions to diffuse isotropically despite the
fundamentally anisotropic structure of graphite, resulting, inter
alia, in favorable charge/discharge and favorable low temperature
performance.
[0039] The novel multi-step process allows the "bottom-up"
construction of highly isotropic composite particles having the
desired electrochemical as well as mechanical properties, wherein
the composite particles are constructed from agglomerated finer
primary particles that have been coated with a carbonaceous binder
material which upon carbonization at higher temperatures (typically
between 1850 and 3500.degree. C.) is converted to graphitic or
non-graphitic material stably connecting the multiplicity of fine
particles resulting in a characteristic spherical porous shape
resembling a "snowball-like", framboidal or "rose bud-like"
morphology (see FIGS. 1 to 4 for details).
[0040] Such composite particles differ from merely agglomerated
graphite particles in that they exhibit an increased mechanical
stability due to the connection of the primary particles through
the carbonized binder material acting as a "glue", thereby stably
holding together the finer particles in a random orientation. Some
embodiments of the carbonaceous composite materials described
herein are unique in view of the random or near-random orientation
of the finer primary particles and the presence of isotropically
distributed pores within the composite particles, combined with an
excellent mechanical stability, allowing the particles to withstand
any significant damage/breakdown during the electrode manufacturing
process.
[0041] The above-described morphology of the aggregated and
optionally coated single particles in the composite particle allows
access of the electrolyte through large pores, favoring the lithium
diffusion in the solid because the diffusion paths in the solid are
reduced to the size of the primary particles of the aggregated
particles. This is different to typical amorphous carbon-coated
spherical graphite particles where, for example in the case of a
pitch coating process, the amorphous carbon coating will be present
at the particle surface, thus also potentially blocking/closing the
pores of the agglomerated carbonaceous particles. The lack of
electrolyte-accessible pores will increase the path for the lithium
diffusion to the dimension of the particle, thus no longer allowing
the direct wetting with the liquid electrolyte.
Carbonaceous Composite Particles
[0042] Thus, a first aspect of the present disclosure relates to
carbonaceous composite particles, wherein said composite particles
are comprised of a multiplicity of aggregated primary particles,
wherein said primary particles are held together by a carbonaceous
binder material attached to the surface of the primary particles.
These composite particles are further characterized by any one or a
combination of the following parameters:
(i) a good pressure stability, wherein the BET specific surface
area (BET SSA) does not increase by more than 3.5 m.sup.2/g, or
more than 3.0 m.sup.2/g, or more than 2.5 m.sup.2/g, or more than
2.0 m.sup.2/g, or more than 1.5 m.sup.2/g, or more than 1.0
m.sup.2/g after pressing at 15 kN/cm.sup.2 for 10 s (see Materials
and Methods section below for the details how the pressure test of
the particles is conducted); alternatively or in addition wherein
the BET specific surface area (BET SSA) after pressing at 15
kN/cm.sup.2 for 10 s does not increase by more than 100%, or more
than 80%, or more than 60% compared to the BET specific surface
area of the material before pressing; (ii) a mass loss of
non-graphitic carbon according to thermogravimetric analysis (TGA)
of less than 5%, or less than 4%, or less than 3%, or less than 2%,
or less than 1%, or less than 0.5% (see again Materials and Methods
section below for details on the TGA measurement); and/or (iii) a
surface crystallinity expressed by an L.sub.a of >4 nm, or >6
nm, or >10 nm, as determined by measuring the I.sub.D/I.sub.G
band amplitude ratio via Raman spectroscopy.
[0043] The term "aggregated" used in the context of the
carbonaceous composite particles shall be understood to refer to a
connection through some additional carbon (graphitic or
non-graphitic) on the surface of the primary particles (the
additional carbon is referred to as "carbonaceous binder material"
in the present disclosure). This is in contrast to a mere
"agglomeration", where the finer particles are merely held together
through relatively weak inter particle interactions (mainly van der
Waals forces). Said additional carbon acting as the "glue" holding
together the primary particles is derived from a carbonaceous
binder precursor material attached to the surface of the primary
particles (coating) which has subsequently been converted to
non-graphitic or graphitic carbon by a heat treatment of the
agglomerated intermediate particles.
[0044] It will be understood that the mass loss of any
non-graphitic carbon (which may for the purpose of the mass loss
parameter include pyrolyzed carbon) generally depends on the
thickness and structure of the carbon on the surface of the
particles, which in turn depends on the process parameters as well
as on the amount and carbon yield of the carbon source employed for
the coating of the primary particles. For example, at high
temperature (>1850.degree. C.), the binder precursor material is
converted almost completely into graphitic or non-graphitic carbon
exhibiting very few heteroatoms or defects. Consequently, it was
found that the mass loss of primarily pyrolyzed carbon was less
than 0.5% in the working examples below, demonstrating that only
traces of pyrolyzed or amorphous carbon remain on the surface of
the particles.
[0045] As can be seen from sample materials obtained according to
the process of the present disclosure (cf. FIGS. 1 to 4), the
carbonaceous composite particles may be further characterized by a
"snowball-like", or "framboidal", or "rose bud-like" morphology,
i.e. a distinctive round shape consisting of a multiplicity of
distinct smaller primary particles stably connected through the
carbon bridges, as described above.
[0046] In some embodiments, the carbonaceous composite particles
may be further characterized by a near-random or random orientation
of the primary particles forming the aggregated composite
particle.
[0047] Yet another feature that may be used to characterize certain
embodiments of the carbonaceous composite particles described
herein is that the particles are rather isotropic in terms of their
electrical, mechanical, and/or heat-conductive properties, as
compared to, for example highly oriented pyrolytic graphite (HOPG)
that exhibits anisotropic electrical conductivity by a factor of
1000. Isotropic in the present context should be understood to mean
that the respective properties of the particles in different
directions does not differ by more than a factor of 40, or more
than a factor of 20 or more than a factor of 10 (e.g. as reflected
by measured [004]/[110] XRD ratios of <4 or even <3), in
contrast to anisotropic unmodified natural or synthetic graphite.
For example, the measured [004]/[110] XRD ratio (area) of the
graphite material 8 in comparative Example 4 is 180.
[0048] The isotropy of the carbonaceous composite particles may in
certain embodiments be further characterized by a ratio of the peak
areas of the [004] and [110] reflections (peak area % [004]/[110])
of lower than 10, or lower than 8, lower than 6, or lower than 4,
or lower than 3, or lower than 2. The small values for the
[004]/[110] ratio of the peak areas reflect the isotropic
distribution of the crystalline domains within the particle, and
thus also the random orientation of the primary particles in the
composite particles. The theoretical [004]/[110] ratio for a fully
isotropic distribution of the crystalline domains would be
1.56.
[0049] In some embodiments, the carbonaceous composite particles
according to the present disclosure may be additionally
characterized by any one of the following parameters, alone or in
combination:
(i) a BET specific surface area (BET SSA) of between 0.3 and 20
m.sup.2/g, or of between 1 and 15 m.sup.2/g, or between 1 and 10
m.sup.2/g, or between 1 and 5 m.sup.2/g; (ii) a crystallite size
L.sub.c of less than 300 nm, or less than 250 nm, or less than 200
nm; (iii) an L.sub.c/L.sub.a ratio of at least 1, or at least 1.5,
or at least 2, or at least 2.5, or at least 3; and/or (iv) a xylene
density (according to DIN 51 901) of at least 2.00 g/cm.sup.3, or
at least 2.10 g/cm.sup.3, or at least 2.15 g/cm.sup.3 or at least
2.20 g/cm.sup.3; (v) a spring-back of between 10 and 90%, or
between 15 and 80%, or between 20 and 70%, or between 30 and 60%;
and/or (vi) the carbonaceous binder material connecting said
primary particles being graphitic, or non-graphitic carbon, or
both.
[0050] With regard to the latter, the carbonaceous binder material
attached to the surface of said primary particles of the
carbonaceous composite particles according to the present
disclosure is in some embodiments graphitic carbon, i.e., the
carbonaceous binder precursor material coating the primary
particles has been converted to graphitic carbon during the heat
treatment step at elevated temperatures above 1850.degree. C. for a
sufficient time to achieve the graphitization of the binder
attaching the primary particles to their neighbors. In such
embodiments, the binder present on the surface of the composite
particles is typically also converted to graphite, which means that
such particles have a relatively high surface crystallinity.
However, since it is not excluded that the resulting composite
particles may be additionally modified subsequently to the heat
treatment, in some embodiments, the surface may also be coated
with, for example, other materials such as amorphous carbon despite
the fact that the binder is still graphitic carbon (e.g. through a
subsequent CVD coating and the like).
[0051] In other embodiments, the carbonaceous binder material
attached to the surface of said primary particles of the
carbonaceous composite particles according to the present
disclosure is non-graphitic carbon, i.e., the carbonaceous binder
precursor material coating the primary particles has only been
carbonized (not converted to graphitic carbon, or not entirely)
during the heat treatment step at elevated temperatures above
1850.degree. C. It is readily apparent that composite particles
where parts of the binder have been graphitized and other parts of
the binder in the composite particles have only been carbonized
represent another possible embodiment of the present disclosure. It
will be understood that the degree of graphitization of the binder
precursor material can be influenced by the conditions and duration
of the heat treatment applied to generate the composite particles
of the present disclosure.
[0052] A related, but independent parameter possibly characterizing
the carbonaceous composite particles is the interlayer distance
c/2. In certain embodiments, the carbonaceous composite particles
are characterized by an interlayer distance c/2 of 0.338 nm or
less, or 0.337 nm or less. Such composite particles are referred to
herein as "graphitic composite particles". In other embodiments,
the carbonaceous composite particles are characterized by an
interlayer distance c/2 of more than 0.338 nm, more than 0.339 nm,
or more than 0.340 nm. Such composite particles are referred to
herein as "non-graphitic composite particles".
[0053] For most applications it is desirable that the average size
of the particles does not exceed 30-40 .mu.m. Since the composite
particles are by definition formed by a multiplicity of primary
carbonaceous particles, the average length of the major axis of the
primary particles as observed by scanning electron microscopy (SEM)
is in certain embodiments between 1 and 15 .mu.m, or between 1 and
10 .mu.m, or between 1 and 7 .mu.m, or even between 1 and 5 .mu.m,
as for example illustrated in FIGS. 1 to 4.
[0054] The primary particles forming the carbonaceous composite
particles may in most embodiments be selected from a carbonaceous
material such as natural graphite, synthetic graphite, graphene,
graphene nanoplatelets, graphene or carbon fibers, fullerenes,
nanographite, hard carbon, soft carbon, petroleum- or coal-based
coke, graphitized fine coke, char, carbon black, carbon nanotubes
(CNT), including single-walled nanotubes (SWNT), multiwalled
nanotubes (MWNT), or mixtures of any of the foregoing. The
carbonaceous material forming the primary particles in the
composite particles described herein may in certain embodiments be
mixed with one or more non-carbonaceous materials, such as silicon,
silicon oxide, tin, tin oxide or tin dioxide, aluminum, bismuth,
lithium titanate, or mixtures of any of the foregoing
non-carbonaceous materials. However, given that the heat treatment
step at elevated temperatures may lead to undesirable chemical
reactions (e.g. as the formation of silicon carbide),
non-carbonaceous primary particles are not preferred.
[0055] In order to achieve a high level of isotropy of the
particles, it is in certain embodiments desirable that even the
primary particles in the composite particles exhibit a shape that
is as spherical as possible. Since natural graphite typically has a
flake-like morphology, it is not possible to provide such spherical
primary particles from unmodified natural graphite, unless they are
ground to a very small size in which case the anisotropic
morphology becomes less pronounced. Thus, modified, rounded
graphite (synthetic or natural) or non-graphitic particles (such as
coke) can be used as primary particles in such embodiments.
Suitable examples include coke, carbon black, graphitized fine
coke, spherical (synthetic or natural) graphite, or micronized
ultrafine or submicron-sized synthetic or natural graphite, and the
like.
[0056] It is apparent that the primary particles may not
necessarily be homogeneous. Thus, in some embodiments the primary
particles are selected from a single material, optionally from a
single carbonaceous material, as listed above. In other
embodiments, the primary particles are selected from at least 2, 3,
4, or at least 5 different carbonaceous or non-carbonaceous
materials. Preferably at least one material forming the primary
particles is a carbonaceous material.
[0057] As explained above, the carbonaceous binder material
connecting the multiplicity of primary particles can be graphitic,
non-graphitic, or both. This does not only depend on the heat
treatment condition and duration, but also on the selection of the
carbonaceous binder precursor material that is converted into
carbon during the formation of the composite particles of the
present disclosure.
[0058] The carbonaceous binder material is, already for reasons of
economy, in some embodiments the same for all primary particles in
the composite particle, i.e. only one type of carbonaceous binder
precursor material has been used for the preparation of the
composite particles. However, in certain embodiments, it may be
advisable to use different carbonaceous binder precursor material,
which may lead to carbonaceous composite particles wherein the
carbonaceous binder material is not identical/different for at
least a portion of the primary particles in the composite particle.
In these embodiments, at least 2, 3, 4, 5, or more different
carbonaceous binder materials may be present in a composite
particle.
[0059] This can be achieved by using at least 2, 3, 4, 5, or more
differing carbon binder precursor materials which result in
different carbon layers after the heat treatment step.
Alternatively, the same carbonaceous binder precursor material or
different carbonaceous binder precursor materials can also lead to
different carbonaceous binders when the multiple carbonaceous
binder precursor materials are attached to the surface of the
primary particles by different coating methods, which may likewise
have an influence on the final structure of the binder inside the
composite particles.
[0060] In terms of suitable techniques for obtaining the
carbonaceous binder material attached to the surface of the primary
particles, these include, but are not limited to the following
techniques generally known in the art:
(i) mixing of primary carbonaceous particles with a carbonaceous
binder precursor material and subsequent carbonization of said
carbonaceous binder precursor material; (ii) mixing of primary
carbonaceous particles with a carbonaceous binder precursor
material and subsequent graphitization of said carbonaceous binder
precursor material; (iii) melting of a carbon precursor onto the
primary particles; (iv) pitch-coating, (v) pyrolysis, (vi)
evaporation.
[0061] Of these, creating a dispersion--with or without
solvent--with the primary carbonaceous particles and the
carbonaceous binder precursor material (e.g. by mixing the two
components together, followed by drying of the dispersion if
necessary), and subsequent agglomeration and heat treatment to
effect conversion of the binder precursor material into
carbonized/graphitized binder holding together the primary
particles in the composite material is particularly suitable due to
its simplicity and possibility to use environmentally friendly
processes and materials, e.g. a coating based on non-hazardous
organic precursor molecules with water as a solvent. However, other
methods to attach the precursor to the surface of the primary
particles can likewise be used, provided the coated particles can
be assembled into agglomerated intermediate particles that undergo
a heat treatment as described herein below in more detail.
[0062] The carbonaceous composite particles according to the
present disclosure may in certain embodiments be further
characterized by a particle size distribution (PSD) of the
composite particles having
(i) a D.sub.90 value ranging from 5 to 70 .mu.m, or from 10 to 50
.mu.m, or from 12 to 30 .mu.m; or from 12 to 25 .mu.m and/or (ii) a
D.sub.50 value ranging from 2 to 30 .mu.m, or from 5 to 25 .mu.m,
or from 10 to 20 .mu.m and/or (iii) a D.sub.10 value ranging from
0.5 to 20 .mu.m, or from 2 to 10 .mu.m, or from 3 to 8 .mu.m.
[0063] In some preferred embodiments, the particle size
distribution value D.sub.90 does not exceed 35 .mu.m, or does not
exceed 30 .mu.m, or does not exceed 25 .mu.m.
[0064] As briefly noted below, in some embodiments, especially when
the heat treatment was not carried out for long enough to fully
graphitize the binder on the surface of the particles, the
carbonaceous composite particles may be further characterized by a
non-graphitic (e.g. pyrolyzed or amorphous) carbon coating on the
surface of the composite particles. This may for example be
assessed by determining the amplitude ratio of the amplitudes of
the D and G bands in RAMAN spectroscopy (I.sub.D/I.sub.G).
[0065] Given that the novel process of the invention allows the use
of non-hazardous carbon precursors for the coating of the primary
particles (i.e. (coal tar) pitch coatings are not required), the
carbonaceous composite particles according to the present
disclosure can in some instances be further characterized by having
a low polycyclic aromatic hydrocarbon (PAH) concentration. The PAH
concentration of these particles in these instances is less than
200 mg/kg, less than 150 mg/kg, less than 100 mg/kg, less than 30
mg/kg, less than 10 mg/kg, less than 5 mg/kg, less than 2 mg/kg,
less than 1 mg/kg, or even less than 0.5 mg/kg.
[0066] Finally, the carbonaceous composite particles may in some
embodiments further comprise an additive selected from the group
consisting of carbon black, colloidal graphite, graphene, graphene
nanoplatelets, graphene or carbon fibers, fullerenes, nanographite,
hard carbon, soft carbon, petroleum- or coal-based coke,
graphitized fine coke, char, carbon nanotubes (CNT), including
single-walled nanotubes (SWNT), multiwalled nanotubes (MWNT),
metals/metalloids such as silicon, aluminum, tin, silver, copper,
nickel, antimony, germanium, metal/metalloid oxides such as
TiO.sub.2, lithium titanate, SiO.sub.x, or SnO.sub.x,
chalcogenides, or metal alloys, optionally wherein the
metals/metalloids are selected from silicon, aluminum, or tin, or
alloys comprising said metals.
[0067] The carbonaceous composite particles are in certain
embodiments further characterized by a Scott density (apparent or
poured density) of above about 0.25 g/cm.sup.3, or above about 0.30
g/cm.sup.3, or above about 0.33 g/cm.sup.3.
[0068] In some embodiments of this aspect of the present invention,
the carbonaceous composite particles may be further characterized
by a porosity determined by mercury intrusion porosimetry of at
least about 50%, or at least about 60%, or at least about 65%, or
70%.
[0069] Finally, the carbonaceous composite particles may in certain
embodiments be further characterized by, inter alia, a high lithium
acceptance, increased power and electrochemical capacity, fast
charge and discharge performance, and favorable low temperature
performance. For example, in certain embodiments the carbonaceous
composite particles described herein may be further characterized
by a charge/discharge rate capability 2 C/0.2 C of at least 97%, or
at least 98%, or at least 99%, or at least 99.5% when present as an
active material in a negative electrode of a lithium-ion battery.
The charge/discharge rate capability is one of the most relevant
properties of cathode materials for lithium batteries that would be
advantageous to improve, in particular when envisaging high power
density applications such as automotive applications.
[0070] Another aspect of the present disclosure relates to
compositions comprising the carbonaceous composite particles as
defined herein.
[0071] In some embodiments, the composition comprising the
carbonaceous composite particles as defined herein is mixed
together with one or more other types of carbonaceous composite
particles as defined herein, but different from the first
carbonaceous composite particles (i.e. mixtures of at least two
different carbonaceous composite particles according to the present
disclosure). For example, composite particles made from different
carbon precursors, such as (non-graphitizable) hard carbon, and
graphitic or graphitizable starting materials, may be combined,
resulting in isotropic carbon active materials that exhibit the
favorable high rate properties of hard carbon-type active materials
(L.sub.c of about 10 nm) and the high capacity provided by
graphitic active materials (with an L.sub.c>70 nm).
[0072] Alternatively or in addition, the composition comprising the
carbonaceous composite particles or the composition comprising a
mixture of at least two types of carbonaceous composite particles
as defined herein may further contain yet another type of
unmodified or modified carbonaceous particles. In particular, as
illustrated in Example 4, it has been found that mixing the
carbonaceous composite particles as described herein with a high
capacity but less spherical graphitic active material, e.g. as
disclosed in WO 2016/008951, may yield an active carbonaceous
material with excellent electrochemical properties. Accordingly, in
some embodiments, the present invention relates to compositions
comprising the carbonaceous composite particles as described herein
in a mixture with one or more high capacity surface-modified
hydrophilic graphite(s).
Process for Preparing Carbonaceous Composite Particles
[0073] One aspect of the present disclosure relates to a novel
process for preparing carbonaceous composite particles such as the
carbonaceous composite particles described and characterized
herein. With the novel process, it is possible to produce highly
isotropic carbonaceous, e.g. graphitic, composite particles that
exhibit advantageous properties in terms of their electrochemical
behavior and their mechanical stability. The combined favorable
properties make such particles an extremely promising active
material in negative electrodes in lithium-ion batteries, for
example in the automotive sector and related areas where it is
important to employ lithium-ion batteries characterized not only by
a high reversible capacity but also by a fast charge and discharge
performance.
[0074] The novel process ensures that the resulting isotropic
composite particles have isotropically distributed pores allowing
high lithium-ion diffusion rates at high charge/discharge currents
and offering a sufficiently high power density of the cell. At the
same time, the process of the present disclosure allows the
production of composite particles that exhibit markedly improved
mechanical properties wherein the aggregated primary particles are
able to withstand pressure and shear forces applied to the
particles during the manufacturing process for making negative
electrodes, for example for lithium-ion batteries. This is due to
the fact that the primary particles forming the isotropic composite
particles are attached to each other through a carbonaceous
(graphitic or non-graphitic) binder, as opposed to the mere
aggregation of primary particles through van der Waals forces as
described in the prior art.
[0075] Hence, in this aspect of the disclosure, the process is a
multi-step process (although several of the steps can be combined
or carried out in a single reactor, as will be explained in greater
detail below). One step of this process generally comprises the
attachment of a carbonaceous binder precursor material to the
surface of carbonaceous particles ("primary particles"), optionally
in the presence of a solvent, thereby forming a coating of the
carbonaceous particles by the carbonaceous binder precursor
material ("step (a)"). If a solvent was used in the coating step
(a), the dispersion is subsequently dried (by any suitable means)
to remove any solvent from the coated particles ("step (b)").
During or after the coating and/or the drying step, the process
further comprises causing agglomeration of the coated primary
carbonaceous particles ("step (c)"). After agglomeration into
composite intermediate particles formed by a multiplicity of coated
primary carbonaceous particles, the dry agglomerated particles are
optionally subjected to a high temperature treatment between about
1850 and 3500.degree. C. so as to yield carbonaceous composite
particles composed of a multiplicity of aggregated primary
particles, wherein said primary particles are held together by a
carbonaceous binder material attached to the surface of the primary
particles ("step (d)").
[0076] In this process, the primary particles are eventually
attached to each other (or "glued" together) by the carbonaceous
binder precursor material which is converted to a carbonaceous or
even graphitic binder during the heat treatment at temperatures of
above 1850.degree. C. up to about 3500.degree. C. (the latter is
for practical and economic reasons a reasonable upper limit for the
maximum temperature during the heating step).
[0077] As apparent from the general description of the process,
this process can be characterized as a "retrosynthetic" or
"bottom-up" process for constructing highly desirable isotropic
graphitic (or non-graphitic) composite particles with a number of
desired properties that can be influenced or fine-tuned by the
appropriate choice of starting materials and process
parameters/conditions, as explained in greater detail herein
below.
[0078] Although not limited to such particles, the carbonaceous
composite particles obtained by the process of the present
disclosure will in most embodiments be characterized by the
parameters as described herein above or in the appended claims.
[0079] Typically, the carbonaceous particles employed in the
coating step ("step (a)") can be selected from the group consisting
of natural graphite, synthetic graphite, graphene, graphene or
carbon fibers, fullerenes, nanographite, hard carbon, soft carbon,
petroleum- or coal-based coke, graphitized fine coke, char, carbon
black, carbon nanotubes (CNT), including single-walled nanotubes
(SWNT), multiwalled nanotubes (MWNT), or mixtures of any of the
foregoing. In certain embodiments, non-carbonaceous materials such
as silicon, silicon oxide, tin, tin oxide or tin dioxide, aluminum,
bismuth, lithium titanate, or mixtures of any of the foregoing may
also be added in particulate form to the carbonaceous primary
particles ("non-homogenous mixture of primary particles").
[0080] As explained above, particularly good results in terms of
their isotropy have been achieved with primary particles that have
less anisotropy than natural graphite flakes. Accordingly, in
certain embodiments, the carbonaceous particles employed in step
(a) are non-graphitic particles, preferably selected from the group
consisting of hard carbon, soft carbon, petroleum- or coal-based
coke, graphitized fine coke, char, carbon black and mixtures
thereof. In some particularly preferred embodiments, the
carbonaceous particles to be coated are selected from fine
petroleum- or coal-based coke, carbon black; optionally mixed
together with graphitic particles.
[0081] The particle size distribution of the carbonaceous particles
employed in step (a) is in most embodiments characterized by a
D.sub.90 of <35 .mu.m, or <30 .mu.m, or <25 .mu.m, or
<20 .mu.m, and/or by a D.sub.50 of <about 20 .mu.m, <about
15 .mu.m, or <about 10 .mu.m. In order to obtain composite
particles that do not exceed a D.sub.50 of about 20 to 25 .mu.m,
the D.sub.90 of the primary particles should be <about 20 .mu.m,
and/or the D.sub.50 should be <about 15 .mu.m.
[0082] In terms of the shape or morphology of the primary
particles, the carbonaceous particles to be coated in step (a) may
exhibit in some embodiments a sphericity Q3 [S=0.8] of equal or
more than 22%, or more than about 30%, 40%, 50%, i.e. more than
e.g. 22% of the primary particles have a sphericity of at least
0.8, as determined by dynamic imaging (see Methods section for
details on how this parameter is determined).
[0083] The term carbonaceous binder precursor material in the
present context should be understood to encompass any suitable
carbon-containing molecule that upon heating in an inert atmosphere
can be converted to pure non-graphitic or graphitic carbon.
[0084] Thus, the carbonaceous binder precursor material to be used
in step (a) of the process is in some embodiments selected from the
group consisting of polymers, such as a lignin-based polymer, a
polystyrene or derivative thereof, a styrene-butadiene copolymer,
melted phenol resin, polyvinylalcohol, polyfurfuryl alcohol,
furfural, polyurethane, polystyrene-acrylate, polyacrylate,
polymethylmethacrylate, polymethacrylonitrile, polyoxymethylene,
poly(methyl atropate), polyisobutene, polyethyleneoxide,
polypropyleneoxide, polyethylene, polypropylene,
polymethylacrylate, polybutadiene, polyisoprene, polyacrylonitrile,
polyaniline, tannic acid, starch, gum arabic, maltodextrin,
formaldehyde phenol resins, formaldehyde tetrahydrofuran resins,
nitrile butyl rubber, sucrose, glucose, or other sugars, polyethyl
ether ketone, polyphenylene sulfide, polyvinyl chloride,
carboxymethylcellulose, methyl cellulose, gelatins, polyvinyl
pyrrolidone, polylactic acid, latexes thereof, a hydrocarbon gas
such as methane, ethane, ethylene, propane, propene, acetylene,
butane, benzene, toluene, xylene, or an alcohol such as ethanol,
propanol, isopropanol (optionally mixed with an inert carrier gas),
and combinations thereof. It will be understood that the choice of
suitable carbonaceous binder precursor material also depends on the
technique to coat, i.e. attach the binder precursor material, to
the surface of the primary carbonaceous particles, as detailed
below.
[0085] While in general not being limited in terms of its weight
ratio, the amount of carbonaceous binder precursor material
relative to the amount of the carbonaceous primary particles is
typically below 30% (w/w), e.g. about 15 to 18%. In some
embodiments, the amount of binder precursor material is about 18%,
or about 15%, or below about 15%, or below about 14%, or below
about 12% or below about 10%, or below about 5% (w/w) of the amount
of carbonaceous primary particles to be coated with the binder
precursor material. The inventors have found that it is possible to
achieve the desired result of producing mechanically stable, highly
isotropic aggregate particles by using a relatively low amount of
binder that is apparently sufficient to stably connect the primary
particles with each other upon conversion of the binder precursor
material to carbon or graphite (see working examples where the
amount of binder precursor material was about 15% to 18%
(w/w)).
[0086] In any event, the carbonaceous binder precursor material
used in step (a) of the process in some embodiments is not or does
not include ammonium lignosulfonate. In other embodiments, the
carbonaceous binder precursor material used in step (a) of the
process is not or does not include coal tar, tar pitch, and
petroleum pitch, and, optionally also no ammonium lignosulfonate.
Substances like coal tar, tar pitch, and petroleum pitch could from
a technical point of view be used in the process of the present
disclosure, but they are clearly undesirable since they are known
or suspected to be carcinogenic or hazardous substances that should
be avoided whenever possible.
[0087] Any suitable method to attach the carbonaceous binder
precursor material to the surface of the primary carbonaceous
particles can be used in the context of the present disclosure. In
certain embodiments, suitable methods to attach the carbonaceous
binder precursor material to the surface of the carbonaceous
primary particles include but are not limited to the following
methods selected from the group consisting of
(i) mixing to form a dispersion, optionally in the presence of a
solvent and subsequent drying; (ii) melting the carbonaceous binder
precursor onto the primary particles; (iii) pyrolysis; and (iv)
evaporation.
[0088] In some embodiments, it is preferred that the coating is
accomplished by mixing the carbonaceous primary particles with the
carbonaceous binder precursor material to form a dispersion.
Preferably, the mixing is carried out in the presence of a
solvent.
[0089] The solvent is typically a polar solvent. The solvent may in
some embodiments be selected from water, methanol, ethanol,
propanol, isopropanol, acetone, or mixtures thereof, with water
being particularly preferred due to its environmentally friendly,
non-hazardous properties.
[0090] In other embodiments, the carbonaceous binder precursor
material may also be melted on the carbonaceous particles, which
may be accomplished by heating the mixture of carbonaceous
particles and the carbonaceous binder precursor material until the
precursor material melts and adheres to the surface of the
carbonaceous particles, thereby forming a coating on the surface of
the carbonaceous primary particles.
[0091] If desired, further additives can in some embodiments be
added during step (a).
[0092] Suitable additives may include but are not limited to citric
acid, ammonia, acetic acid, formic acid, malic acid, stearic acid,
or combinations thereof.
[0093] As noted above, when the coating step (a) includes a
solvent, the solvent must be removed before converting the
carbonaceous binder precursor material attached to the surface of
the primary particles. As a first step, it is often useful to
simply filter off the dispersion (comprising the coated primary
particles) to remove the bulk of the solvent. Any residual solvent
can in principle be removed by suitable, well-known techniques for
removing solvent. Suitable techniques include well-known drying
methods such as freeze-drying, evaporation in a regular atmosphere,
or evaporation under a reduced pressure/vacuum, optionally at
elevated temperatures, or drying in an optionally heated inert gas
stream.
[0094] While the drying step is optional and by definition linked
to the presence of a solvent in step (a), the subsequent
agglomeration of the coated primary particles is at any rate a
mandatory key feature of the process of the present disclosure.
[0095] In general, any suitable method to achieve agglomeration of
the primary particles can be used in step (c) of the process
described and claimed herein. It will be understood that the
process of agglomeration of the primary particles can take place
already during the mixing of binder precursor material and
carbonaceous particles, or, in case a solvent is used, it can be
achieved during the drying step to remove any residual solvent.
However, agglomerates can also be formed after the mixing and
optional drying steps (steps (a) and (b), respectively) by any
suitable technique known in the prior art.
[0096] One well-known suitable technique to achieve agglomeration
of primary (coated) particles is the spray-drying of a dispersion
comprising the primary carbonaceous particles and the carbonaceous
binder precursor material.
[0097] Adjusting the spray-drying conditions allows varying the
particle size of the final particles prior to the subsequent heat
treatment steps. In this regard, the spray formation and consequent
contact of the droplets with the hot air in the chamber are its
main characteristics. It was found that the size of the droplets
created during the atomization step as well as the solvent
evaporation rate correlate strongly with the particle size of the
final product. The hot air flow is typically co-current which
ensures that the spray evaporation is rapid and the dried product
does not experience any significant heat degradation. Once the
solvent fully evaporates from the droplets, the dried product is
entrained in the hot air flow from which it can be separated, for
example by a cyclone. The process parameters such as inlet
temperature, outlet temperature, pump speed, and gas flow for
atomization, of the spray dryer can be optimized individually,
depending on the desired characteristics of the particles, as is
well-known to those of skill in the art. Further details, such as
suitable devices and process conditions, are described in more
detail in the working examples below.
[0098] Additional information can also be taken from
PCT/EP2015/058112 which is incorporated by reference in its
entirety.
[0099] However, the drying of step (b) and the agglomeration of
step (c) may in some embodiments also be achieved by vacuum-drying
a dispersion comprising the primary carbonaceous particles and the
carbonaceous binder precursor material obtained from step (a) in a
heatable vacuum reactor. This drying process will automatically
lead to suitable agglomerates, provided the particle size
distribution of the primary particles allows their agglomeration
under the chosen drying conditions.
[0100] Alternatively, the drying of step (b) and the agglomeration
of step (c) may be achieved by freeze-drying a dispersion
comprising the primary carbonaceous particles and the carbonaceous
binder precursor material obtained from step (a) in a stirred
freeze dryer.
[0101] The drying of step (b) and the agglomeration of step (c) may
in certain embodiments be also achieved by flash-drying a
dispersion comprising the primary carbonaceous particles and the
carbonaceous binder precursor material obtained from step (a) in a
flash dryer.
[0102] Yet another possible way to accomplish the drying of step
(b) and the agglomeration of step (c) is by drying a fluidized
dispersion comprising the primary carbonaceous particles and the
carbonaceous binder precursor material obtained from step (a) in a
fluidized bed dryer, optionally in combination with a spray
system.
[0103] The drying of step (b) and the agglomeration of step (c) may
also be achieved by disc drying a dispersion comprising the primary
carbonaceous particles and the carbonaceous binder precursor
material obtained from step (a) in a disc dryer.
[0104] Alternatively, the drying of step (b) and the agglomeration
of step (c) may be achieved by paddle drying a dispersion
comprising the primary carbonaceous particles and the carbonaceous
binder precursor material obtained from step (a) in a paddle
dryer.
[0105] The drying of step (b) may in some embodiments also include
the filtering of the dispersion comprising the primary carbonaceous
particles and the carbonaceous binder precursor material obtained
from step (a) and drying the resulting filtered cake in one of the
suitable dryers mentioned above.
[0106] The carbonaceous binder precursor material attached to the
surface of the agglomerated particles obtained from step (c) is
then, if necessary, carbonized by subjecting the particles to a
heat treatment under vacuum or an inert atmosphere, optionally
under a nitrogen or argon atmosphere, at temperatures generally
ranging from 400.degree. C. to 3500.degree. C., thereby causing a
thermal decomposition of the precursor material. Temperatures of
about 400.degree. C. to 600.degree. C. are generally regarded as
sufficient to carbonize any carbonaceous precursor material present
on the surface of the primary particles, although higher
temperatures will likewise convert the precursor material to
amorphous carbon or, at temperatures above about 2000.degree. C.,
to graphitic carbon.
[0107] It is therefore apparent that the carbonization of the
precursor may be carried out in a separate heat treatment step
prior to step (d), or it may be carried out as part of the heat
treatment step (d) with a controlled ramp up of the temperatures in
the reactor. In addition, it will be understood that since the
agglomeration step (c) may already use heating, steps (c) and (d)
(and possibly also step (b), i.e. drying of the dispersion) may in
some embodiments also be carried out simultaneously.
[0108] For example, a suitable heating scheme may include heating
the agglomerated particles under vacuum or in an inert atmosphere
first up to 400 to 800.degree. C., keeping the particles at that
temperature for a sufficient time to carbonize the precursor
material and to remove any gases from the thermal decomposition of
the precursor material, followed by increasing the temperature to
above 1850.degree. C. (and up to 3500.degree. C.) and keeping the
particles for a sufficient time to convert at least a portion of
any amorphous carbon derived from the precursor material to
graphitic carbon. Alternatively, the carbonization can also be
carried out in a separate step and/or a separate reactor.
[0109] In any event, it is in certain embodiments preferred to
first carbonize the precursor material at lower temperatures of
between 400.degree. C. to 800.degree. C. to allow the complete
removal of any gases generated by the thermal decomposition of the
precursor material, before heating the agglomerated particles to
temperatures above 1850.degree. C. to obtain the stable, highly
isotropic composite particles composed of aggregated primary
particles connected to each other by the non-graphitic or graphitic
binder.
[0110] In some embodiments of this aspect of the disclosure, it is
preferred that the heat treatment of step (d) is carried out at
temperatures and for a sufficient time to convert any non-graphitic
carbon in the intermediary agglomerated particles obtained from
step (c) to graphitic carbon. In other embodiments, the heating
step (d) will not convert all amorphous carbon to graphitic carbon.
In both cases, particles exhibiting favorable electrochemical and
mechanical properties have been obtained.
[0111] The process may in certain embodiments encompass a
pre-treatment step prior to the heat treatment step (d), wherein
the coated agglomerated carbonaceous particles are subjected to a
pre-treatment performed under vacuum, air, nitrogen, argon or a
CO.sub.2 atmosphere at temperatures of below 1100.degree. C., or
below 700.degree. C. to modify the surface of the agglomerated
particles.
[0112] In yet other embodiments, the process may also include an
additional heat treatment step ("post-treatment step") after step
(d). In this post-treatment step, the composite particles obtained
from step (d) are subjected to an additional heat treatment in a
gas atmosphere such as nitrogen, argon, mixtures of nitrogen with
hydrocarbons like acetylene, propane or methane, or with oxidative
gases such as air, steam, or CO.sub.2 to adjust the morphology and
surface chemistry of the carbonaceous composite particles. The
post-treatment is typically carried out at temperatures of between
300.degree. C. and 1500.degree. C. In some embodiments, this
additional heat treatment step ("post-treatment step") is performed
by contacting the composite particles with an oxidant either in a
gaseous/solid phase process with air, carbon dioxide, water vapor,
oxygen, ozone, or any combination thereof, or, alternatively, in a
liquid/solid phase process with aqueous hydrogen peroxide or other
oxidants present in said liquid phase. Such a post-treatment may
for example be employed in order to increase the hydrophilicity of
the resulting particles. Further information on the aforementioned
post-treatment steps may for example be found in WO 2013/149807 or
in PCT/EP2015/066212, both to Imerys Graphite & Carbon, which
are incorporated by reference in their entirety.
[0113] Another possible post-treatment step (i.e. after step (d))
may in some embodiments include an additional coating step of the
resulting composite particles, such as a CVD coating or a PVD
coating and the like. It is readily apparent that a subsequent
coating with an amorphous carbon layer will change the surface
characteristics of the resulting composite particles (in the case
of CVD coating for example a lower BET SSA, lower porosity, a lower
surface crystallinity, etc.).
[0114] In a particularly preferred embodiment, the process is
carried out with fine (D.sub.90 below 20 .mu.m and a D.sub.50 of
below 10 .mu.m) non-graphitic carbonaceous particles as a starting
material. Such non-graphitic particles (e.g. fine coke or carbon
black) are already less anisotropic than graphite particles. These
particles are then coated with a carbonaceous binder precursor
material in the presence of a solvent. The resulting dispersion is
subsequently spray-dried to cause removal of the solvent and
agglomeration of the primary, coated particles. The obtained
agglomerated intermediate particles are then subjected to a heat
treatment, first at around 400 to 600.degree. C. and then to a heat
treatment at above 1850.degree. C. in order to generate the
carbonaceous (and in many instances at least partially graphitic)
composite particles described herein. Such a process is for example
described in further detail in the Examples below.
[0115] The resulting carbonaceous composite particles obtained by
the process described herein exhibit favorable electrochemical and
mechanical properties as explained above.
[0116] Accordingly, a further aspect of the present invention
therefore relates to carbonaceous composite particles as described
herein which are obtainable by a process according to the present
invention, as described in detail in the present disclosure. The
carbonaceous composite particles obtainable from the process of the
invention are in some embodiments characterized by the parameters
as set out herein above and in the appended claims.
Compositions Comprising Carbonaceous Composite Particles
[0117] Another aspect of the present invention relates to
compositions comprising said carbonaceous composite particles. In
some embodiments of this aspect, the composition comprises mixtures
of carbonaceous composite particles, wherein the particles are
different from each other, e.g. made by a different process or with
different starting materials. The compositions may in other
embodiments furthermore, or alternatively, comprise other
unmodified (e.g. natural or synthetic graphite) or modified
carbonaceous, e.g. graphitic or non-graphitic particles. Thus, in
other words, compositions comprising carbonaceous composite
particles according to the present disclosure with other
carbonaceous or non-carbonaceous materials, in various ratios (e.g.
from 1:99 (% w/w) to 99:1 (% w/w)) are also contemplated by the
present disclosure. In certain embodiments, unmodified graphite may
be added to the carbonaceous composite particles at various stages
of making the products described herein.
Uses and Secondary Products Comprising the Carbonaceous Composite
Particles
[0118] Yet another aspect of the present invention relates to the
use of the carbonaceous composite particles or the composition
comprising said carbonaceous composite particles as described
herein for preparing a negative electrode material for lithium-ion
batteries. Another, related aspect of the present disclosure
relates thus to a negative electrode of a lithium-ion battery
and/or to a lithium-ion battery comprising the carbonaceous
composite particles or the composition comprising said carbonaceous
composite particles as described herein as an active material in
the negative electrode of the battery. For instance, a composition
comprising a binder and the carbonaceous composite particles or the
composition comprising said carbonaceous composite particles as
described herein could be used to produce a negative electrode.
[0119] In yet another aspect, the present disclosure relates to an
energy storage device comprising the carbonaceous composite
particles or the composition comprising said carbonaceous composite
particles as described herein.
[0120] A further aspect of the present disclosure relates to a
carbon brush comprising the carbonaceous composite particles or the
composition comprising said carbonaceous composite particles as
described herein.
[0121] Polymer composite materials comprising the carbonaceous
composite particles or the composition comprising said carbonaceous
composite particles as described herein represent another aspect of
the present disclosure.
[0122] An electric vehicle, hybrid electric vehicle, or plug-in
hybrid electric vehicle which comprises a lithium-ion battery,
wherein the lithium-ion battery comprises the carbonaceous
composite particles or the composition comprising said carbonaceous
composite particles as described herein as an active material in
the negative electrode of the battery is another aspect of the
present disclosure. In some embodiments of this aspect, the
carbonaceous particles comprise only graphitic material, while in
other materials the carbonaceous particles may also comprise
non-graphitic material.
[0123] Due to the larger size of sodium ions as compared to
lithium-ions, sodium ions typically do not undergo intercalation
with graphite, but are rather adsorbed on the carbon surface,
especially inside pores with a sufficiently large diameter. The
importance of isotropic electrolyte-filled pores with low
tortuosity in order to obtain favorable sodium-ion diffusion in
negative electrodes is however analogous to lithium-ion battery
electrodes. Thus, a sodium-ion battery comprising the carbonaceous
composite particles or the composition comprising said carbonaceous
composite particles as described herein represents another aspect
of the present invention.
[0124] Yet another aspect of the present disclosure relates to a
carbon-based coating exhibiting isotropic electric, mechanical or
heat-conducting properties, wherein said coating comprises the
carbonaceous composite particles or the composition comprising said
carbonaceous composite particles as described herein. A related
aspect thus refers to the use of said carbon-based coating as a
coating of current collectors in batteries.
[0125] Dispersions comprising the carbonaceous composite particles
or the composition comprising said carbonaceous composite particles
as described herein are yet another aspect of the present
disclosure. Such dispersions are typically liquid solid
dispersions, i.e. they also include a solvent. Suitable solvents
may in some embodiments include water, or N-methyl-2-pyrrolidone
(NMP), both commonly used as solvents for carbon-based
dispersions.
[0126] Finally, the present disclosure relates to a method for
preparing a building block of a negative electrode, employing the
carbonaceous composite particles or the composition comprising said
carbonaceous composite particles as described herein. Given that
the composite particles already have a near optimal shape and pore
distribution, the use of the carbonaceous composite particles as
described herein in the manufacture of negative electrodes allows
dispensing additional steps that must otherwise be included to
ensure that the graphite particles in the electrode are distributed
in an isotropic fashion (i.e. avoiding a preferred orientation in
case of conventional anisotropic graphite particles). The composite
particles therefore represent a "pre-fabricated" building block
that can be used in the manufacture of negative electrodes for
lithium-ion batteries.
[0127] The concept of preparing a building block for a negative
electrode that exhibits both, favorable energy density and
favorable charge/discharge performance at C-rates of 2 C (i.e. a
charge/discharge within 30 min) or faster was further developed by
preparing "snowball" carbon powders based on both coke and graphite
(cf. Example 4 and Table 4 below) as precursor material. The latter
allows the fine-tuning of the pore size distribution in order to
achieve an optimal Li-diffusion in the electrode, as indicated by
the characterization of the materials through mercury
porosimetry.
[0128] Furthermore, it was demonstrated that mixing such snowball
carbon powders with high capacity but less spherical graphitic
active materials (e.g. 30% snowball carbon powder and 70% high
capacity graphite, see Example 4), leads to a dramatic power
performance increase (cf. Table 5). Accordingly, by mixing snowball
carbon powders with high capacity graphites, energy density, power
performance as well as production costs can be favorably adjusted
to specific applications, such as automotive batteries (employed in
electric vehicle, hybrid electric vehicle, or plug-in hybrid
electric vehicle), grid storage batteries, or batteries for other
applications.
Methods
BET Specific Surface Area (BET SSA)
[0129] The method is based on the registration of the absorption
isotherm of liquid nitrogen in the range p/p.sub.0=0.04-0.26, at 77
K. Following the procedure proposed by Brunauer, Emmet and Teller
(Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc.,
1938, 60, 309-319), the monolayer adsorption capacity can be
determined. On the basis of the cross-sectional area of the
nitrogen molecule, the monolayer capacity and the weight of the
sample, the specific surface area can then be calculated.
BET Specific Surface Area after Pressing at 15 kN/cm.sup.2
[0130] The BET Specific Surface Area is measured as described above
after pressing the powder sample in a piston with a press force of
15 kN/cm.sup.2 for 10 s (pressing ramp duration: 5 s). More
specifically, 0.5 g of a graphite/carbon powder sample were
inserted between 2 steel discs into a pellet press (PIKE
Technologies, USA) with a cylindrical hole diameter of 13 mm. The
steel piston (PIKE Technologies, USA) was inserted into the
cylindrical hole. With a hydraulic press (P/O/Weber, Germany) an
automatic protocol was run as follows:
1) increase press force from 0 kN to 20 kN (15 kN/cm.sup.2) over
the course of 5 s; 2) keep press force constant at 20 kN for 10 s;
3) decrease press force from 20 kN to 0 kN over the course of 5 s.
After completion of the protocol and repetition of the procedure in
order to obtain sufficient material, the BET specific surface area
of the powder was measured as described above.
X-Ray Diffraction
[0131] XRD data were collected using a PANalytical X'Pert PRO
diffractometer coupled with a PANalytical X'Celerator detector. The
diffractometer has the following characteristics shown in Table
1:
TABLE-US-00001 TABLE 1 Instrument data and measurement parameters
Instrument PANalytical X'Pert PRO X-ray detector PANalytical
X'Celerator X-ray source Cu--K.sub..alpha. Generator parameters 45
kV-40 mA Scan speed 0.07.degree./s (for L.sub.c and c/2)
0.01.degree./s (for [004]/[110] ratio) Divergence slit 1.degree.
(for L.sub.c and c/2) 2.degree. (for [004]/[110] ratio) Sample
spinning 60 rpm
[0132] The data were analyzed using the PANalytical X'Pert
HighScore Plus software.
Interlayer Spacing c/2
[0133] The interlayer space c/2 is determined by X-ray
diffractometry. The angular position of the peak maximum of the
[002] and [004] reflection profiles are determined and, by applying
the Bragg equation, the interlayer spacing is calculated (Klug and
Alexander, X-ray Diffraction Procedures, John Wiley & Sons
Inc., New York, London (1967)). To avoid problems due to the low
absorption coefficient of carbon, the instrument alignment and
non-planarity of the sample, an internal standard, silicon powder,
is added to the sample and the graphite peak position is
recalculated on the basis of the position of the silicon peak. The
graphite sample is mixed with the silicon standard powder by adding
a mixture of polyglycol and ethanol. The obtained slurry is
subsequently applied on a glass plate by means of a blade with 150
.mu.m spacing and dried.
Crystallite Size L.sub.c
[0134] Crystallite size is determined by analysis of the [002] and
[004] X-ray diffraction profiles and determining the widths of the
peak profiles at the half maximum. The broadening of the peak
should be affected by crystallite size as proposed by Scherrer (P.
Scherrer, Gottinger Nachrichten 2, 98 (1918)). However, the
broadening is also affected by other factors such X-ray absorption,
Lorentz polarization and the atomic scattering factor. Several
methods have been proposed to take into account these effects by
using an internal silicon standard and applying a correction
function to the Scherrer equation. For the present disclosure, the
method suggested by Iwashita (N. Iwashita, C. Rae Park, H.
Fujimoto, M. Shiraishi and M. Inagaki, Carbon 42, 701-714 (2004))
was used. The sample preparation was the same as for the c/2
determination described above.
[004]/[110] ratio
[0135] The isotropicity of the crystallites is determined by the
ratio of the intensity and/or by the ratio of the area between the
[004] and the [110] XRD peaks. The intensity and the area of the
peaks are determined after applying a peak fitting program using
the PANalytical X'Pert HighScore Plus software. The samples are
prepared as a slurry on a Mylar foil which is then dried. During
the blading of the slurry on the foil, an alignment of flaky
particles occurs. Through this blading procedure, a preferred
orientation of anisotropic particles such as graphite is
introduced.
[0136] If crystallites are arranged in an anisotropic fashion on
the Mylar foil, the [004]/[110] ratio of the peak areas is very
high (i.e. in a preferred orientation). By contrast, if
crystallites are oriented randomly, the [004]/[110] ratio is low.
Ratios are reported based on peak area and intensity.
Crystallite Size L.sub.a by Raman Spectroscopy
[0137] Raman analyses were performed using a LabRAM-ARAMIS
Micro-Raman Spectrometer from HORIBA Scientific with a 632.8 nm
HeNe LASER. The ratio I.sub.G/I.sub.D is based on the ratio of peak
amplitudes of band D and band G. These peaks are characteristic for
carbon materials, measured at 1580 cm.sup.-1 and 1350 cm.sup.-1,
respectively.
Crystallite size L.sub.a is calculated from Raman measurements
using the equation
L.sub.a[nm]=C*(I.sub.G/I.sub.D),
where the constant C has a value of 5.8 nm for lasers with a
wavelength of 632.8 nm (A. C. Ferrari, Solid State Comm. 2007, 143,
47-57).
Particle Size Distribution by Laser Diffraction
[0138] The presence of particles within a coherent light beam
causes diffraction. The dimensions of the diffraction pattern are
correlated with the particle size. A parallel beam from a low-power
laser is irradiated on a cell which contains the sample suspended
in water. The beam leaving the cell is focused by an optical
system. The distribution of the light energy in the focal plane of
the system is then analyzed. The electrical signals provided by the
optical detectors are transformed into the particle size
distribution by means of a calculator. A small sample of graphite
is mixed with a few drops of wetting agent and a small amount of
water. The sample prepared in the described manner is introduced
into the storage vessel of the apparatus and measured.
References: ISO 13320-1/ISO 14887
Xylene Density
[0139] The analysis is based on the principle of liquid exclusion
as defined in DIN 51 901. Approx. 2.5 g (accuracy 0.1 mg) of powder
is weighed in a 25 ml pycnometer. Xylene is added under vacuum (20
mbar). After a few hours dwell time under normal pressure, the
pycnometer is conditioned and weighed. The density represents the
ratio of mass and volume. The mass is given by the weight of the
sample and the volume is calculated from the difference in weight
of the xylene filled pycnometer with and without sample powder.
Reference: DIN 51 901
Scott Density (Apparent Density)
[0140] The Scott density is determined by passing the dry carbon
powder through the Scott volumeter according to ASTM B 329-98
(2003). The powder is collected in a 1 in 3 vessel (corresponding
to 16.39 cm.sup.3) and weighed to 0.1 mg accuracy. The ratio of
weight and volume corresponds to the Scott density. It is necessary
to measure three times and calculate the average value. The bulk
density of graphite is calculated from the weight of a 250 mL
sample in a calibrated glass cylinder.
Reference: ASTM B 329-98 (2003)
Spring-Back
[0141] Spring-back is a source of information regarding the
resilience of compacted graphite powders. A defined amount of
powder is poured into a die. After inserting the punch and sealing
the die, air is evacuated from the die. A compression force of
about 1.5 tons/cm.sup.2 is applied and the powder height is
recorded. This height is recorded again after the pressure has been
released. Spring-back is the height difference in percent relative
to the height under pressure.
Mercury Intrusion Porosimetry
[0142] The method is based on the measurement of the amount of
mercury intrusion versus the pressure applied to a sample immersed
in mercury. On the basis of the applied pressure, the surface
tension of mercury and the contact angle between mercury and the
solid surface, the pore size can be calculated. The experiments
were performed on a sample (ca. 0.1-0.3 g) over the pressure range
of 0.5-4000 bar using a Micromeritics Autopore III machine. For
treating the data, a contact angle of 130.degree. and a surface
tension of 485.times.10.sup.-3 N/m were used. The porosity of a
sample is determined from the following equation:
Porosity = Specific pore volume Specific pore volume + 1 / xylene
density ##EQU00001##
where the specific pore volume is determined as the volume of
mercury intruded per gram of sample, including interparticle and
intraparticle porosity. The volume of mercury which causes the
initial settling of the sample due to the exerted pressure is not
included. Reference: ISO 15901-1:2005(E)
Thermogravimetric Analysis (TGA)
[0143] The determination of the percentage of mass loss of any
pyrolyzed carbon is performed by using conventional
thermogravimetric equipment (TGA). A sample of ca. 20-30 mg was
used for the measurements. The atmosphere in the thermogravimetric
equipment is pure oxygen with a flow rate of 10 mL/min (with
initial purging of 30 mL/min) with a heating rate of 5.degree.
C./min up to 1000.degree. C. followed by an isotherm of 2 hours.
Pyrolyzed carbon can be distinguished from graphitic or
non-graphitic carbon as it burns off at lower temperature.
Dynamic Image Analysis
[0144] The sphericity and the aspect-ratio of the particles of the
material were obtained from an image analysis sensor, which is a
combination of particle size and shape analysis. The experiments
were performed using a Sympatec QICPIC sensor and a MIXCEL
dispersing unit. The material was prepared as a paste with water
and a surfactant (liquid detergent). The instrument uses a high
speed camera (up to 500 fps) and a pulsed light source to capture
clear rear-illuminated images of entrained particles. The
measurement time varied between 30-60 seconds with an average of
more than 500000 measured particles. Each sample was repeated three
times for reproducibility measurements. The software program
determines all of the parameters for the particles.
Sphericity
[0145] The sphericity, S, is the ratio of the perimeter of the
equivalent circle (assuming the particles are circles with a
diameter such that it has the same area of the projection area of
the particle), P.sub.EQPC, to the real perimeter, P.sub.real. The
Q.sub.3 (S=0.8) value mentioned herein corresponds to the
percentage of particles (by cumulative volume) which have a
sphericity lower than S=0.8. Accordingly, a small percentage
indicates a sample with highly spherical particles as the majority
of the particles in the sample have a sphericity greater than
0.8.
[0146] Additionally, k.sub.S,.rho. is a parameter expressing the
ratio of the percentage Q.sub.3 (S=0.8) versus the decrease in
xylene density from the theoretical value for graphite (which is
2.26 g/cm.sup.3):
k.sub.S,.rho.=Q.sub.3(S=0.8)/(2.26-xylene density)
[0147] For non-graphitic (coke) particles coated with amorphous
carbon, k.sub.S,.rho. is a parameter expressing the ratio of the
percentage Q.sub.3 (S=0.8) versus the decrease in xylene density
from the value observed for average uncoated coke particles (which
is 2.1 g/cm.sup.3):
k.sub.S,.rho.=Q.sub.3(S=0.8)/(2.1-xylene density)
PAH Concentration
[0148] The concentration of polycyclic aromatic hydrocarbons PAH
was determined by the Grimmer method and the analyses were
performed externally by BIU-Grimmer (Germany). The Grimmer method
generally used for PAH analysis is based on a stable isotope
dilution methodology using GC-MS(SIM) for quantification in the sub
ppb range.
Lithium-Ion Negative Electrode Half Cell Test--Standard
Procedure
[0149] This test was used to quantify the reversible and
irreversible capacity of the surface-modified coated carbonaceous
particles.
General Half-Cell Parameters:
[0150] 2 Electrode coin cell design with Li metal foil as
counter/reference electrode, cell assembly in an argon filled glove
box (oxygen and water content <1 ppm).
Diameter of Electrodes:
[0151] 13 mm A calibrated spring (100 N) was used in order to have
a defined force on the electrode. Tests were carried out at
25.degree. C.
Dispersion Formulation:
[0152] 97% graphite/coke, 1% CMC (Sodium-carboxymethylcellulose),
2% SBR (styrene-butadiene rubber)
Dispersion Preparation:
[0153] Add the carbon powder to the CMC solution (1.5% in water)
and homogenize with a dissolver disk for 20 min at reduced pressure
at 600 rpm. Add the SBR latex (46% in water) and further homogenize
for 20 min.
Blading Height on Cu Foil:
[0154] 200 .mu.m (doctor blade).
Drying Procedure:
[0155] Coated Cu foils were dried for 1 h at 80.degree. C.,
followed by 12 h at 120.degree. C. under vacuum (<50 mbar).
After cutting, the electrodes were dried for 10 h at 120.degree. C.
under vacuum (<50 mbar) before insertion into the glove box.
Pressing of Electrodes:
[0156] As indicated in Tables 3 and 4, electrodes were either
measured without pressing, or were pressed to a density of 1.5-1.7
g/cm.sup.3 using a hydraulic press.
Electrolyte:
[0157] Ethylenecarbonate (EC): Ethylmethylcarbonate (EMC) 1:3, 1 M
LiPF.sub.6 was used for all examples.
Separator:
[0158] Glass fiber sheet, ca. 1 mm.
Cycling Program Using a Potentiostat/Galvanostat:
[0159] 1.sup.st charge: constant current step 20 mA/g to a
potential of 5 mV vs. Li/Li.sup.+, followed by a constant voltage
step at 5 mV vs. Li/Li' until a cutoff current of 5 mA/g was
reached. 1.sup.st discharge: constant current step 20 mA/g to a
potential of 1.5 V vs. Li/Li.sup.+, followed by a constant voltage
step at 1.5 V vs. Li/Li' until a cutoff current of 5 mA/g was
reached. 2.sup.nd charge: constant current step at 50 mA/g to a
potential of 5 mV vs. Li/Li.sup.+, followed by a constant voltage
step at 5 mV vs. Li/Li' until a cutoff current of 5 mA/g was
reached. 2.sup.nd discharge: constant current step at 3 C to a
potential of 1.5 V vs. Li/Li.sup.+, followed by constant voltage
step at 1.5 V vs. Li/Li' until a cutoff current of 5 mA/g was
reached.
Power Performance
[0160] 2 C was applied to the fully charged cell to a potential of
1.5V vs. Li/Li.sup.+. The power performance was defined as the
obtained capacity divided by the reversible capacity of the
2.sup.nd cycle.
[0161] Having described the various aspects of the present
disclosure in general terms, it will be apparent to those of skill
in the art that many modifications and slight variations are
possible without departing from the spirit and scope of the present
disclosure.
[0162] Some of these embodiments will now also be described by way
of illustration, with reference to the following examples.
EXAMPLES
Example 1
[0163] 30 g of ammonium lignosulfonate were dissolved in 600 mL of
deionized water while stirring vigorously with a dissolver disc.
200 g of coke precursor 1 (properties listed in Table 1 below) were
slowly added, followed by further mixing for 2 h. This dispersion
was spray-dried using a Buchi B-290 laboratory spray dryer, using a
2-fluid nozzle in co-current mode with an inlet temperature of
170.degree. C. and an air gas flow rate of 700 L/h, resulting in a
carbonaceous powder that was collected in the product collection
vessel attached to the cyclone. In a glass tube carbonization oven,
this powder was heated to 450.degree. C. under a nitrogen
atmosphere over the course of 1 h, followed by further treatment at
450.degree. C. for 1 h. Heat treatment in an argon atmosphere (ramp
up to 2'000.degree. C.: 10.degree. C./min, ramp from
2'000-3'000.degree. C.: 5.degree. C./min, followed by 4 h at
3'000.degree. C.) resulted in carbon powder 4 (see Table 2).
Example 2
[0164] 30 g of ammonium lignosulfonate were dissolved in 600 mL of
deionized water while stirring vigorously with a dissolver disc.
200 g of coke precursor 2 (properties listed in Table 1 below) were
slowly added, followed by further mixing for 2 h. This dispersion
was spray-dried using a Buchi B-290 laboratory spray dryer, using a
2-fluid nozzle in co-current mode with an inlet temperature of
170.degree. C. and an air gas flow rate of 700 L/h, resulting in a
carbonaceous powder that was collected in the product collection
vessel attached to the cyclone. In a glass tube carbonization oven,
this powder was heated to 450.degree. C. under a nitrogen
atmosphere over the course of 1 h, followed by further treatment at
450.degree. C. for 1 h. Heat treatment in an argon atmosphere (ramp
up to 2'000.degree. C.: 10.degree. C./min, ramp from
2'000-3'000.degree. C.: 5.degree. C./min, followed by 4 h at
3'000.degree. C.) resulted in carbon powder 6 (see Table 2).
Alternatively, heat treatment after carbonization at 450.degree. C.
in an argon atmosphere (ramp up to 1'800.degree. C.: 10.degree.
C./min, followed by 4 h at 1'800.degree. C.) resulted in carbon
intermediate 5 (see Table 2).
Example 3
[0165] 30 g of ammonium lignosulfonate were dissolved in 600 mL of
deionized water while stirring vigorously with a dissolver disc.
200 g of coke precursor 3 (properties listed in Table 1 below) were
slowly added, followed by further mixing for 2 h. This dispersion
was spray-dried using a Buchi B-290 laboratory spray dryer, using a
2-fluid nozzle in co-current mode with an inlet temperature of
170.degree. C. and an air gas flow rate of 700 L/h, resulting in a
carbonaceous powder that was collected in the product collection
vessel attached to the cyclone. In a glass tube carbonization oven,
this powder was heated to 450.degree. C. under a nitrogen
atmosphere over the course of 1 h, followed by further treatment at
450.degree. C. for 1 h. Heat treatment in an argon atmosphere (ramp
up to 2'000.degree. C.: 10.degree. C./min, ramp from
2'000-3'000.degree. C.: 5.degree. C./min, followed by 4 h at
3'000.degree. C.) resulted in carbon powder 7 (see Table 2).
Example 4
[0166] 300 g of ammonium lignosulfonate were dissolved in 6'000 mL
of deionized water while stirring vigorously with a dissolver disc.
1'100 g of coke precursor 9 and 600 g of graphite precursor 10
(properties listed in Table 3 below) were slowly added, followed by
further mixing for 2 h. This dispersion was spray-dried using a
pilot scale spray dryer, using a 2-fluid nozzle in co-current mode
with an inlet temperature of 220.degree. C. and an air gas pressure
of 3 bar, resulting in a carbonaceous powder that was collected in
the product collection vessel attached to the cyclone. In a
carbonization oven, this powder was heated to 450.degree. C. under
a nitrogen atmosphere over the course of 1 h, followed by further
treatment at 450.degree. C. for 1 h. Heat treatment in an argon
atmosphere (ramp up to 2'000.degree. C.: 10.degree. C./min, ramp
from 2'000-3'000.degree. C.: 5.degree. C./min, followed by 4 h at
3'000.degree. C.) resulted in carbon powder 11. The physicochemical
parameters of carbon powder 11 are shown in Table 4. In
electrochemical tests, the carbon powder 11 was mixed with graphite
active material 12 (a synthetic graphite with a hydrophilic
coating, as described in WO 2016/008951) in a 3:7 weight ratio, and
the mixture was used to prepare negative electrodes. The
electrochemical data for the active graphite mixture 13 are
reported in Table 4 and 5. As shown in FIGS. 5 and 6, the analysis
by means of SEM of the cross-sections for these electrodes shows
that the snow-ball morphology of the secondary graphite particles
is essentially maintained even in the pressed electrode.
Comparative Example 5
[0167] Heat treatment of coke precursor 1 (properties listed in
Table 1 below) in an argon atmosphere (ramp up to 2'000.degree. C.:
10.degree. C./min, ramp from 2'000-3'000.degree. C.: 5.degree.
C./min, followed by 4 h at 3'000.degree. C.) resulted in carbon
powder 8 (see Table 2).
Results
TABLE-US-00002 [0168] TABLE 2 Properties of Carbon Precursors Coke
Coke Coke precursor 1 precursor 2 precursor 3 Particle size
D.sub.10 (.mu.m) 3.3 2.9 3.8 D.sub.50 (.mu.m) 7.8 6.9 9.0 D.sub.90
(.mu.m) 15.0 13.2 16.2 BET SSA 4.7 13.3 19 (m.sup.2/g) Xylene
density 2.13 2.077 1.534 (g/cm.sup.3) Scott density 0.22 0.26 0.44
(g/cm.sup.3) Interlayer distance c/2 (nm) 0.3486 0.3490 0.3561
Crystallite size L.sub.c (nm) 4 2.9 2
TABLE-US-00003 TABLE 3 Properties of Carbonaceous Composite
Particles Carbon powder 8 Carbon Carbon Carbon Carbon (comparative
powder 4 intermediate 5 powder 6 powder 7 example) Particle size
D.sub.10 (.mu.m) 7.5 7.6 6.7 n.d. 2.9 D.sub.50 (.mu.m) 14.9 15.6
14.1 7.5 D.sub.90 (.mu.m) 25.9 29.0 26.0 14.1 BET SSA 1.7 2.1 1.9
n.d. 2.9 (m.sup.2/g) BET SSA 2.4 3.1 2.7 n.d. n.d. (m.sup.2/g)
after pressing at 15 kN/cm.sup.2 Xylene density 2.254 2.161 2.251
2.029 2.256 (g/cm.sup.3) Scott density 0.30 n.d. 0.35 n.d. 0.19
(g/cm.sup.3) Interlayer 0.3363 0.3482 0.3364 0.3438 0.3362 distance
c/2 (nm) Crystallite size 108 10 86 10 132 L.sub.c (nm) Crystallite
size 58 4 n.d. n.d. n.d. L.sub.a (nm) [004]/[110] 2.08 n.d. 1.59
n.d. 147 (intensity) [004]/[110] 3.36 n.d. 2.26 n.d. 180 (area)
Mass loss of 0.2 n.d. 0.2 0.3 n.d. pyrolyzed carbon (TGA) [%]
Reversible 324 n.d. n.d. 181 n.d. capacity 2.sup.nd cycle (mAh/g),
unpressed electrodes Irreversible 6.3 n.d. n.d. 18.2 n.d. capacity
1.sup.st cycle [%], unpressed electrodes
TABLE-US-00004 TABLE 4 Properties of Carbonaceous Composite
Particles based on a Coke/Graphite Precursor Mixture Active
Material 13 (mixture of carbon Graphite powder 11 and Coke Graphite
Carbon Active material 12 @ precursor 9 precursor 10 powder 11
Material 12 weight ratio 3:7) Particle size n.d. D.sub.10 (.mu.m)
1.4 2.4 5.6 7.4 D.sub.50 (.mu.m) 7.3 6.0 15.5 17.2 D.sub.90 (.mu.m)
19.7 12.3 33.3 34.9 BET SSA 19.2 15.2 2.1 3.4 n.d. (m.sup.2/g) BET
SSA n.d. n.d. 2.8 n.d. n.d. (m.sup.2/g) after pressing at 15
kN/cm.sup.2 Xylene density 2.052 2.25 2.22 2.217 n.d. (g/cm.sup.3)
Interlayer 0.3493 0.3358 0.3365 0.3357 n.d. distance c/2 (nm)
Crystallite size 3 99 72 147 n.d. L.sub.c (nm) Reversible n.d. n.d.
325 358 347 capacity 1.sup.st cycle (mAh/g) Irreversible n.d. n.d.
7.9 8.2 8.3 capacity 1.sup.st cycle [%] Hg- n.d. n.d. 69.2 n.d.
n.d. porosimetry
[0169] Several materials were also examined in terms of their
electrochemical properties, in particular regarding their specific
charge and coulombic efficiency. Specific charge obtained in the
first electrochemical lithium insertion and subsequent de-insertion
cycle, the coulombic efficiency of the first insertion/de-insertion
cycle, the direct current resistance (DCR) and the high rate
performance of the electrode at 2 C (specific charge of the
half-cell obtained by a complete discharge in 30 minutes)
normalized to the specific charge at 0.2 C (5 h discharge).
TABLE-US-00005 TABLE 5 Electrochemical Parameters Active Material
13 (mixture of carbon Spherical coated powder 11 and natural
graphite Carbon Graphite Active material 12 @ (reference material)
powder 11 Material 12 weight ratio 3:7) Specific charge 1.sup.st
392.0 353.1 389.7 377.7 lithium insertion in mAh/g Specific charge
1.sup.st 359.8 325.0 357.6 346.5 lithium de- insertion in mAh/g
Coulombic 91.8 92.2 91.8 91.7 efficiency (1.sup.st charge/discharge
cycle) in % DCR in Ohm 19.5 24.2 23.8 26.3 Specific charge 98.2
99.9 97.5 99.0 retention (rate capability) at 2 C/0.2 C in %
[0170] Additionally, the pore volume distribution was determined by
mercury porosimetry for several carbonaceous materials (a synthetic
graphite, a spherical natural graphite and carbon powder 11), see
also FIG. 8 for a graphical representation of the results.
TABLE-US-00006 TABLE 6 Pore Volume Distribution by Mercury
Porosimetry >10 .mu.m 5-10 .mu.m 1-5 .mu.m 0.1-1 .mu.m Synthetic
Graphite 0.3 0 0.7 0 Spherical Natural Graphite <0.1 0 0.3 0.1
Graphite Powder 11 0.2 0 0.8 0
* * * * *