U.S. patent application number 16/929248 was filed with the patent office on 2021-01-21 for electrode particles suitable for batteries.
This patent application is currently assigned to PHILLIPS 66 COMPANY. The applicant listed for this patent is PHILLIPS 66 COMPANY. Invention is credited to Christopher J. LaFrancois, Nan Li, Zhenhua Mao, Dachuan Shi, Corey W. Tropf.
Application Number | 20210020904 16/929248 |
Document ID | / |
Family ID | 1000004974555 |
Filed Date | 2021-01-21 |
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United States Patent
Application |
20210020904 |
Kind Code |
A1 |
Mao; Zhenhua ; et
al. |
January 21, 2021 |
ELECTRODE PARTICLES SUITABLE FOR BATTERIES
Abstract
The disclosure relates to a carbon-based electrode material that
has been graphitized to hold ions in the electrode of a battery and
more particularly include carbide or carbide and nitride surfaces
that protect the graphite core. The preferred batteries include
metal ion such as lithium ion batteries where the carbon-based
electrode is the anode although the carbon-based electrode may also
serve in dual ion batteries where both electrodes may comprise the
graphitized carbon-based electrodes. The electrodes are more
amorphous than conventional graphite electrodes and include a
carbide or nitride containing surface treatment.
Inventors: |
Mao; Zhenhua; (Bartlesville,
OK) ; Li; Nan; (Owasso, OK) ; Tropf; Corey
W.; (Bartlesville, OK) ; Shi; Dachuan;
(Bartlesville, OK) ; LaFrancois; Christopher J.;
(Bartlesville, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHILLIPS 66 COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
PHILLIPS 66 COMPANY
Houston
TX
|
Family ID: |
1000004974555 |
Appl. No.: |
16/929248 |
Filed: |
July 15, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62875318 |
Jul 17, 2019 |
|
|
|
62875299 |
Jul 17, 2019 |
|
|
|
62875315 |
Jul 17, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/133 20130101;
H01M 2004/027 20130101; H01M 10/0525 20130101 |
International
Class: |
H01M 4/133 20060101
H01M004/133; H01M 10/0525 20060101 H01M010/0525 |
Claims
1. A graphitic carbon powder comprising particles having a mean
average particle size of between 1 .mu.m and 50 .mu.m where the
particles comprise at least 99% by weight of carbon graphite with a
modified surface comprising carbide compounds that comprise at
least 5 ppm and no more than 1% by weight of the particles.
2. The graphitic carbon powder according to claim 1 where the
particles have a mean average particle size between 3 .mu.m and 30
.mu.m.
3. The graphitic carbon powder according to claim 2 where the
particles have a mean average particle size between 3 .mu.m and 25
.mu.m.
4. The graphitic carbon powder according to claim 1 where the
particles are at least 99.5% carbon graphite by weight and at least
50 ppm carbide compounds.
5. The graphitic carbon powder according to claim 1 where the
particles are at least 99.9% carbon graphite by weight.
6. The graphitic carbon powder according to claim 1 where the
particles are at least 99.99% carbon graphite by weight
7. The graphitic carbon powder according to claim 1 where the
particles further comprise at least 5 ppm nitride compounds.
8. The graphitic carbon powder according to claim 7 where the
particles include a core and external surface and the core
comprises graphite and the external surface comprises the carbide
compounds and nitride compounds in the form of crystals where the
crystals are at least along the periphery or outer surface of the
particles and comprise at least 50 ppm by weight of the powder and
no more than 2000 ppm by weight.
9. The graphitic carbon powder according to claim 1 where the
carbide compounds comprise at least one selected from Ti, Y, Zr,
Nb, Mo, La, Ce, B, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application which
claims benefit under 35 USC .sctn. 119(e) to U.S. Provisional
Application Ser. Nos. 62/875,318, 62/875,299 and 62/875,315, all
filed on Jul. 17, 2019 and each entitled "ELECTRODE PARTICLES
SUITABLE FOR BATTERIES," which are all incorporated herein in their
entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
FIELD OF THE INVENTION
[0003] This invention relates to batteries and particularly to
materials useful for making the anode for batteries and more
particularly useful for the anode in metal ion batteries.
BACKGROUND OF THE INVENTION
[0004] Rechargeable lithium-ion batteries have been extensively
adopted in many portable systems and devices such as cell phones,
tablets, computers, handheld portable tools and new devices that
are being developed relying on the power and weight advantages of
lithium ion batteries. The advantages are light weight, high
voltage, high electrochemical equivalence and good conductivity.
The broad uses and acceptance of lithium ion batteries has come
through many advances and developments. One area of development for
lithium-ion batteries has been focused on the anode or negative
electrode of lithium-ion batteries where much has been
accomplished.
[0005] The key considerations for anodes for lithium ion batteries,
especially for portable devices is high volume and weight specific
capacity and long battery life over many multiple charge and
discharge cycles. In prior work, anode materials were produced with
initial coulombic efficiency approaching 95% with long life through
coated and graphitized carbon precursor materials. This is
described in U.S. Pat. No. 7,323,120 to Mao et al. where petroleum
coke is ground to a preferred size, subjected to a solvent coating
process, having the coating oxidatively stabilized at an elevated
temperature and then the whole particle carbonized and graphitized
at even higher temperature in an inert environment. The particles
formed highly graphitic structures with a protective coating on the
surface that protected the underlying graphite sheets from the
electrolyte of the battery. The protective coating protects the
edges of graphite sheets which are believed to be catalytically
active for the electrolytes in batteries. The electrolytes thereby
decompose the graphite sheets during the charging cycle and thereby
quickly and drastically reduce the efficiency and storage capacity
for lithium ions in the anode. The coating created on anode
particles comprised a layer of poorly graphitizable material that
when graphitized with the rest of the particle formed a more stable
graphite with respect to catalytic decomposition from the
electrolyte, but not suitable for itself intercalating lithium
ions. But lithium ions are able to easily pass through the coating
and intercalate into the more organized graphite sheets. Indeed,
this is very good material with good properties and good cycle
life. However, its production requires the use of substantial
volumes of solvent along with multiple successive separate heat
treatments in different atmospheres, all of which add up to be
expensive. But, for high value uses where high specific capacity is
needed in a compact space and minimal weight are important, this
anode is currently most advantageous.
[0006] The most important parameters of graphite negative electrode
materials for lithium-ion batteries are the initial coulombic
efficiency and specific capacity. It has been well known that
highly crystalline graphite powders have high specific capacity and
very poor initial coulombic efficiency and are not usable as
negative electrode material for lithium-ion batteries. Through many
years of extensive research and development, sophisticated
processes have been developed to mitigate the problems related to
specific capacity and the initial coulombic efficiency; the major
solutions concentrate on high temperature graphitization and
coating the particles with poorly graphitizable carbon before
graphitization to provide protection from the electrolyte for the
underlying graphite sheets in the particles. Because the mean
average particle size of graphite negative electrode materials is
smaller than 30 microns and individual particles must be uniformly
coated with poorly graphitizable carbon, graphite negative
electrode materials are currently manufactured through complicated
processing steps. As a result, the production cost is high and for
some coating processes, product yield is low.
[0007] With all materials, higher performance at lower cost are
continuous drivers and any progress in either performance or cost
would be very desirable.
BRIEF SUMMARY OF THE DISCLOSURE
[0008] The invention relates to a graphitic carbon powder
comprising particles having a mean average particle size of between
1 .mu.m and 50 .mu.m where the particles comprise at least 99% by
weight of carbon graphite with a modified surface comprising
carbide compounds that comprise at least 5 ppm and no more than 1%
by weight of the particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A more complete understanding of the present invention and
benefits thereof may be acquired by referring to the follow
description taken in conjunction with the accompanying drawings in
which:
[0010] FIG. 1 is schematic view of a battery cell in a hypothetical
circuit showing the anode, cathode, electrolyte and a circuit.
DETAILED DESCRIPTION
[0011] Turning now to the detailed description of the preferred
arrangement or arrangements of the present invention, it should be
understood that the inventive features and concepts may be
manifested in other arrangements and that the scope of the
invention is not limited to the embodiments described or
illustrated. The scope of the invention is intended only to be
limited by the scope of the claims that follow.
[0012] First, turning to FIG. 1, a schematic battery is indicated
by the arrow 10. The battery includes multiple particles of cathode
material 20 and multiple particles of anode material on the
opposite side of an electrolyte separator 40. Each of the particles
of cathode 20 and anode 30 are held in an electrically conductive
paste (not specifically shown) to a respective metal electrode. An
electric load, indicated at 50, such as a light or electric motor
may be attached to the battery 10 with wiring shown at 51. When
battery 10 is charged, positive ions are stored in the anode
particles 30. Due to the electro-chemical natures of the cathode
and anode materials, the positive ions are urged (attracted and
repelled, respectively) to move from the anode 30 through the
electrolyte separator 40 and into the cathode. While the ions move
through the electrolyte, electrons pass around through the metal
electrode 31 and through the wiring 51 and load 50 to the cathode
to balance the electrical charge. The process of passing the
electrons through the load causes electrical work to be
accomplished such as illuminating a light bulb or turning an
electric motor. For lithium-ion batteries, the cathode is generally
formed of a lithium bearing chemical structure that forms lithium
ions during charging of the battery that transit across the
separator 40 and intercalate into the anode. Anode materials are
less chemically complex and high performing anode materials may
densely store the lithium ions in a manner where they are easily
liberated fully back to the cathode without permanent bonding into
the anode. This invention focuses on the makeup of the anode
material used in batteries like that shown in FIG. 1.
[0013] While carbon-coated anode materials have proven to be very
attractive properties for high value batteries where low weight and
compact size are important, in contrast, there are lower value uses
for batteries where weight and size are not as critical. Such lower
value uses include fixed location energy storage devices where very
high energy capacity is needed such as, for example, standby power
for a power distribution grid.
[0014] In looking at batteries to meet those needs, studies have
been undertaken to develop battery designs that use a larger volume
of uncoated, graphitized petroleum coke materials to offset the
expected decay of anode performance over multiple cycles of
charging and discharging. In the process of exploring optimal
graphitization levels for batteries, some graphite nucleating
agents were added to accelerate the formation of graphitic
structure at lower temperatures. However, the end result was a
rather high performing anode material and further developmental
work quickly turned to understanding the nature of the new anode
product and why it performed at a higher level than expected.
[0015] What is believed to have occurred in these tests is that
rather than nucleating graphite formation, the nucleating agents
have reacted with the carbon surface of the particles forming a
carbide compounds or reacted with nitrogen gas to form nitride
compounds at the surfaces of the particles. The carbide and nitride
compounds do not appear to form deep into the particle thereby
preserving the bulk of the particle as crystalline graphite for ion
intercalation. The carbides and nitrides apparently protect the
graphite structure from the electrolyte in the metal ion batteries
thereby preventing the electrolyte from interacting with the
graphite. It is commonly known that electrolytes break down the
graphite in the anode and yet the small thickness of this modified
surface has preserved the graphite sheets in the present
invention.
[0016] Initial studies began with boron as the nucleating agent.
Since graphitizing must be conducted in a non-oxygen environment or
the carbon with burn-off principally forming carbon dioxide,
graphitizing is typically performed under a non-oxygen blanket gas.
Under a nitrogen blanketing gas, nitrides may also be formed on the
surface. However, for some nucleating agents, the nitride form may
boil off and not remain on the surface. The stable nitrides and/or
carbides are best seen to form when the graphitizing temperature is
above the melting point of the stable carbide or nitride molecules
but below their boiling points. For nucleating agents that form
stable nitrides that boil below the graphitizing temperature, other
blanketing gases may be chosen that are inert. Argon has been
successfully used in those circumstances. Referring to Table 1,
potential nucleating agents are shown with representative carbides
and nitrides that may be formed during graphitizing. Referring to
Table 2, the respective coulombic efficiency and specific capacity
are shown for representative batteries made with boron used as a
carbide or nitride forming agent.
TABLE-US-00001 TABLE 1 Melting Boiling Melting Point Point Point
Element Carbide (.degree. C.) (.degree. C.) Nitride (.degree. C.) B
B.sub.4C 2350 >3500 BN 2967 Ce CeC.sub.2 2250 CeN La LaC.sub.2
LaN Mn Mn.sub.3C 1520 Mn.sub.2N.sub.3, >1800 MnN Mo MoC 2577 MoN
2577 Mo.sub.2C 2687 Mo.sub.2N 2687 Nb NbC 3608 4300 NbN 2050
Nb.sub.2C 3080 Si SiC 2830 Si.sub.3N.sub.4 1900 Ti TiC 3067 TiN
2947 V VC 2810 VN 2050 V.sub.2C 2167 Y YC.sub.2 2400 YN Zr ZrC 3532
ZrN 2952
[0017] The carbide and nitride forming materials are blended with
the powdered coke at about 0.1 wt % to about 5 wt %. It is believed
that the carbides and nitrides form on the surface of the particles
as the underlying carbon forms the graphitic structures within.
Thus, the inventive process for making the anode powder includes
preparing the graphite precursor to the desired size by milling or
other known process and adding a suitable amount of the carbide or
nitride forming elements by blending together and then subjecting
the blended mixture to graphite forming temperature for a time
duration sufficient to form the surface chemistry and the
underlying graphite structure. For some coke materials, it may be
preferred to carbonize them to drive off hetero-atoms and other
non-carbon atoms prior to graphitizing by calcining. Carbonizing is
typically a heat-treating process that is below graphite
temperatures but well elevated such as between 900.degree. C. and
1500.degree. C. and typically in a calciner to increase the carbon
content of the coke to at least 92% or a higher content such as 95%
or at least 97%.
[0018] Preferably, the surfaces of the particles are continuous in
either carbides or a mixture of carbides and nitrides leaving no
graphite exposed to the electrolyte. It is also preferred that the
surface would be preferably smoother versus coarse or jagged to the
extent that would be obtainable. Most graphite materials have a
jagged surface where the graphite sheets are more prone to
fracturing as the particles are sized. A smooth surface is believed
to be much more resistant to electrolyte attack on the bulk
graphite structure and that is achieved in the prior art by
coating. The carbide surface can range from a few atoms thick,
resulting in a modified surface that is a few nanometers thick and
may be thicker depending on the selected carbide forming compound
or compounds, but does not alter the jagged surface to the more
desirable smooth surface. The weight content of such a
carbide-forming surface or elements in the graphitized powders can
range from about 50 ppm up to about 5000 ppm, also depending on the
selected compound or compounds.
[0019] The types of cokes and carbide-forming compounds were
discovered to also play important roles in forming desirable
graphite anode materials. The selected cokes are preferably
calcined or at least partially calcined at a temperature between
500 and 2000.degree. C. before graphitization. Green cokes,
particularly those with high volatile matter may react with the
selected carbide-forming compound to form volatile compounds,
resulting in evaporation of such elements before forming stable
carbide at graphitization temperature. On the other hand, cokes
that are carbonized or graphitized at a temperature above
2000.degree. C. are more chemically stable and do not have the
chemical reactivity with the selected carbide-forming compounds
such as salts and oxides, resulting in evaporation of such added
salts or oxides during temperature ramping on graphitization.
[0020] The atmosphere under which the mixtures of coke and carbide
forming compounds are graphitized is a factor in selecting such
carbide forming compounds. Non-oxidizing gases such as argon,
helium, and nitrogen are preferred for graphitization. However, in
the case of nitrogen gas atmosphere, some carbide-forming elements
may also react with nitrogen to form undesirable nitride compounds,
particularly those volatile nitride compounds that dilute or
diminish carbide contents. Thus, the selection of the
carbide-forming compounds is limited to those elements that form
high temperature carbides and/or nitrides. For graphitization in
argon or other non-reactive gases, the preferred carbide-forming
elements form stable carbides at temperatures above 2000.degree. C.
In other words, the best results are where the melting point of the
resulting carbides is above 2500.degree. C., and preferably above
2700.degree. C.
[0021] Moreover, this form of anode material is not coated with a
graphite precursor (or carbon layer that is different from the
bulk). The invention alters the existing surface to have carbide
compounds or carbide and nitride compounds formed on the surface
that protects the core of the particles through many charging and
discharging cycles. So, without the highly graphitic crystallinity
at the surface which is chemically reactive with the electrolyte
the nitride or carbide or both at the surface cause the decay of
the bulk graphite material to be substantially reduced or
eliminated thereby reducing one mode of battery deactivation.
[0022] This would suggest that anode material comprising coke
whether from petroleum or coal tar could be sized by any of a
number of methods to get a mean average particle size so that most
of the particles are between about 3 microns and up to about 30
microns which could then be graphitized in an inert atmosphere up
to about 3100.degree. C.
[0023] Measuring particle size is subject to many viewpoints. In
the preferred invention, particle size may be tailored to the
battery use or to a battery manufacturer's specifications. Ideally,
the particles are substantially similar size considering
variabilities of milling, sieving and other sizing technology. And
the fact that the particles are not likely to be spherical adds an
additional level of complexity. Fortunately, particle size
measurement does not need to be complicated. In general, using
laser diffraction or imaging systems made by Malvern or Horiba
using volume-based calculations provides reasonable accuracy for
purposes of providing such anode powders for use in lithium ion
batteries. And by these measurements, the mean average particle
size within the useful powders are typically between 1 and 50
microns and more typically within a narrower range.
[0024] So, this invention provides a new graphite electrode
material for lithium-ion batteries and also provides a simpler
process for manufacturing such electrode materials. In one
embodiment related to the graphite anode materials, the graphite
particles contain metal or non-metal carbide and nitride components
on particle surfaces, such a carbide or nitride content ranges
between 5 ppm and 1% by weight, preferably between 50 ppm and 2000
ppm, but more preferably less than about 1500 ppm and even more
preferably between about 100 ppm and about 1000 ppm. The carbide
and nitride may be single element or a mixture of different
elements. The amount that is blended into with the carbon precursor
is between about 500 ppm and 10 weight percent, but more preferably
between 1000 ppm and 3 weight percent. The mean average particle
size for the anode particles ranges between 3 and 30 microns and
preferably between 3 and 25 microns.
[0025] The process for producing the graphite materials includes
two primary steps: milling graphitizable carbon precursors to
specified particle sizes and then graphitizing the resulting
powders with the carbide and nitride forming materials at a
specific temperature range. In a little more detail, the carbon
precursors are selected from petroleum and coal tar cokes. Green
cokes are preferred. The selected carbon precursors are milled to a
powder having a mean particle size of less than 30 .mu.m, depending
on specific battery requirements by any mechanical milling method
such as ball-milling, knife-milling, impact-milling, and
jet-milling. Typical mean particle sizes range from 3 .mu.m to 25
.mu.m. Optionally, the milled powders are carbonized in a
non-oxidizing environment to eliminate non-carbon elements. It
should be noted that sizing is preferred before graphitizing as
graphitizing makes the particles more brittle yielding more jagged
and irregular shaped particles which are more vulnerable to
catalytic decomposition of the graphite sheet structures.
[0026] The milled powders (carbonized or green) are combined with
carbide and nitride forming compounds and graphitized in an inert
environment such as nitrogen, argon, helium or combinations thereof
at the temperature higher than 2650.degree. C., preferably between
2800.degree. C. and 3000.degree. C. The carbide and nitride forming
compounds may be transition metals, non-metals, rare earth metals
and combinations thereof. The quantity of the carbide or nitride
forming compounds used is between 100 ppm and 10% by weight of the
total mass, preferably between 0.05 wt % and 2 wt %.
EXPLANATION OF EXAMPLES
[0027] The usefulness of such produced materials is assessed as the
negative electrode material (lithium intercalation) in coin cells
with lithium metal as the counter electrode. The preparation
procedure is described below:
[0028] Electrode preparation--Each electrode was fabricated with
the following steps: Step 1) About 2 g of the graphitized powder
and 0.043 g of carbon black, 0.13 g of polyvinylidene difluoride
(PVDF) (in 10 wt % solution (in N-methyl pyrrolidinone (NMP)) were
placed in a 25-ml plastic vial and shaken with about 3 g of 1/8''
steel balls for 10 min in a mill to form uniform paste. Additional
NMP was added to make the mixture more flowable as needed. Step 2)
A thin film of the resulting paste was cast on a copper foil or
aluminum foil with a doctor-blade coater. The resulting film was
dried on a hot plate at 120.degree. C. for at least 2 hours. Step
3) The dried film was trimmed to a 5-cm wide strip and densified
through a roller press. Step 4) Three disks (1.5 cm in diameter) of
each film were punched out with a die cutter as electrodes. The
electrode weight was determined by subtracting the total weight of
each disk by the weight of the disk substrate. The electrode
composition was 92 wt % graphite, 6 wt % PVDF, and 2 wt % carbon
black, and the mass loading was about 10 mg/cm2.
[0029] Each coin cell was subjected to electrochemical tests. The
coins each consists of bottom can, lithium metal as the counter
electrode, separator, disk electrode, stainless steel disk spacer,
wave spring, and top can. These components were sequentially placed
in the bottom can. The electrolyte was added to the separator
before the disk electrode was stacked. An electrolyte of 1 M LiPF6
in 40 vol % ethylene carbonate, 30 vol % dimethyl carbonate, and 30
vol % diethylene carbonate mixture was used. After the top can was
dropped onto the stack, the assembly was transferred to the coin
cell crimper and crimped together.
[0030] The electrochemical tests were performed on an
electrochemical test station with the different charge/discharge
test programs for negative electrode and positive electrode
materials, respectively, as follows:
[0031] As negative electrode material for lithium-ion batteries--A)
charging at a constant current of -1.0 mA to 0.0 V, B) further
charging at 0.0 volt for one hour, C) discharging at 1 mA until the
voltage reached 2.0 volt, and D) repeating steps A through C 5
times or for 5 cycles. The electrical charge passed during charging
and discharging on each cycle was recorded and used to calculate
the specific capacity and coulombic efficiency. All the tests were
conducted at ambient temperature and the cells were tested in a
glove box where oxygen and moisture levels were below 3 ppm.
Analysis of Carbide and Nitride Forming Element Contents
[0032] After graphitization, the powders are dissolved in acid
solution and analyzed for the elemental contents by standard
inductively coupled plasma mass spectrometry.
Example Set 1
[0033] Two petroleum green coke samples were acquired from
different sources and dried, crushed, and milled to a mean average
particle size of 5 .mu.m. The first sample was from a Phillips 66
refinery in Ponca City, Okla. and the second sample was LXP from a
second Phillips 66 refinery in Lake Charles, La. Each of the
powders were blended with 1 wt % and 2 wt % elemental boron (<1
.mu.m mean particle size) and compared to a sample of powder
without boron. The mixtures were graphitized in argon environment
at 2900.degree. C. and were subsequently assessed as a negative
electrode material for a lithium-ion battery. For comparison, these
anode powders were graphitized under same conditions. Table 2 lists
the discharge specific capacities and initial coulombic
efficiencies for such graphitized powders. Without boron, the
initial coulombic efficiencies are very low (<40%) and the
discharge capacities are also low (-300 mAh/g). Such materials are
not suitable for use as a negative electrode material for
lithium-ion batteries. With boron, the graphitized powders exhibit
excellent properties as negative electrode material for lithium-ion
batteries (high capacity >350 mAh/g and initial coulombic
efficiency >91%).
TABLE-US-00002 TABLE 2 Initial Coulombic Specific Capacity
Efficiency (%) (mAh/g) Boron Coke Coke Coke Coke (wt%) Sample 1
Sample 2 Sample 1 Sample 2 0 37 40 298 301 1 90.3 92.2 354.0 359.6
2 92.7 89.8 355.3 357.0
Example Set 2
[0034] Additional coke sample powder of Coke Sample 1 from Example
Set 1 was graphitized with several blends of Boron and other
carbide and nitride forming elements. Six examples were created
each with 1.5 wt % of a blend. The blends comprised boron and
cerium at three different ratios of boron to cerium of 1:10, 10:1,
and 1:1. These carbide and nitride forming compounds were selected
from metal and non-metal chemicals and graphitized in a nitrogen
atmosphere at 2900.degree. C. The graphitized powders were
evaluated in the same way as those in Example Set 1. Table 3 lists
the discharge specific capacities and initial coulombic
efficiencies for such graphitized powders. The fourth and fifth
columns show the elemental contents of the carbide and nitride
forming elements in the powders after graphitization. The first
three samples exhibited an initial coulombic efficiency greater
than 91% and specific capacity greater than 335 mAh/g, which
demonstrates that high performance anode graphite powders can be
produced economically according to this invention.
[0035] Referring to Table 3 below, it should be quite apparent that
at 2900.degree. C. graphitization temperature, the carbide forming
element causes a physical difference in the resulting electrode
that provides a huge boost to the initial coulombic efficiency. The
carbide forming elements have high melting points and seem to cause
the carbon at the surface to form carbide crystals or accept
(accommodate) nitride crystals at the surface that both allow ions
to pass easily in and out of the graphite while at the same time
protecting the graphite from the electrolyte.
TABLE-US-00003 TABLE 3 Mixture of Carbide and Nitride Specific
Coulombic forming capacity efficiency Boron Cerium elements (mAh/g)
(%) (ppm) (ppm) B and Ce 336.2 93.6 474 248 (1:10) B and Ce 342.3
91.9 3060 165 (10:1) B and Ce 340.0 94.0 185 174 (1:1)
Example Set 3
[0036] A sample of green, anode grade petroleum coke that is
typically used in making anodes for aluminum smelting was dried at
100.degree. C., crushed in a roller mill, and pulverized with a
laboratory jet mill to a mean average particle size of 5 .mu.m.
This sample of coke has a volatile content of 12 weight percent and
was divided into six separate samples. The first three samples were
blends of boron and cerium and the last three were silicon,
manganese and yttrium at about 1.5 weight percent. Each group in
separate small crucibles was placed in a large graphite container
and graphitized at 2900.degree. C. for 15 minutes in an argon gas
environment.
[0037] The graphitized powders were evaluated as anode material for
lithium-ion batteries in coin cells, as described above. The
critical parameters are the specific discharge capacity and initial
coulombic efficiency, and the results were listed in Table 4. The
contents of the carbide forming elements in the graphitized samples
are listed in Table 9. The graphitized samples with a significant
content of carbide forming elements yielded an excellent initial
coulombic efficiency (>92%) and specific capacity, and those
with an undetectable content of carbide forming element showed poor
initial coulombic efficiency (<60%) and low specific
capacity.
TABLE-US-00004 TABLE 4 Example Set 3 Initial Specific Coulombic
Graphite capacity efficiency sample (mAh/g) (%) Boron and 352.7
91.7 Cerium (10:1) Boron and 339.1 93.7 Cerium (1:10) Boron and
335.8 93.7 Cerium (1:1) Silicon 320.0 62.4 Manganese 323.8 66.3
Yttrium 315.0 93.9
Example Set 4
[0038] The same set of the mixtures as those in Example Set 3 was
graphitized in the same way at a temperature of 2900.degree. C. but
in a nitrogen gas environment. The resulting graphite powders were
evaluated in the same way as Example Set 3. The resulting specific
capacities and initial coulombic efficiencies for these samples are
listed in Table 5 below. The measured properties are similar to
those in Example Set 3 except that yttrium that showed diminished
performance in the initial coulombic efficiency. The carbide
forming material also forms nitrides with the nitrogen gas that
evaporates at a temperature lower than the graphitization
temperature and it is believed that the surface treatment did not
stay on the particles rendering them unsuitable as anode material
in a metal ion battery.
TABLE-US-00005 TABLE 5 Example Set 4 Initial Specific Coulombic
Graphite capacity efficiency sample (mAh/g) (%) Boron and 342.3
91.9 Cerium (10:1) Boron and 340.0 94.0 Cerium (1:10) Boron and
336.2 93.6 Cerium (1:1) Silicon 319.1 56.9 Manganese 322.1 57.2
Yttrium 308.0 54.1
[0039] These examples show that the graphitized powders with the
presence of carbide-forming elements exhibit excellent properties
as anode material for lithium-ion batteries, the ones without a
content of such carbide-forming element do not have the desirable
property (low coulombic efficiency).
Example Set 5
[0040] For the Set 5 of the Examples, three grades of green
petroleum coke were dried at 100.degree. C., crushed in a roller
mill, and pulverized with a laboratory jet mill to a mean average
particle size of 5, 8, 11 and 15 .mu.m, respectively. The resulting
coke powders were heated in nitrogen gas at 950.degree. C. for two
hours to remove the volatile matter. These coke powders are labeled
as A, B, and C in the examples described below where A is an
aluminum anode grade petroleum coke, B is a premium petroleum coke
of the type that is used for anodes in electric arc furnaces for
making recycled steel, and C is a lower grade premium petroleum
coke which has been used as a precursor for making anodes in metal
ion batteries having elevated volatile content.
[0041] A sample of various coke particles are blended including 11
.mu.m powder of coke A, 5 and 8 .mu.m powders of coke B, and a 15
.mu.m powder of coke C along with two carbide-forming compounds
(element boron and cerium oxide) with the weight content of 0.5%
and 1.5%. The resulting mixtures were graphitized under the same
conditions as Example Set 4 and tested as anode material for
lithium-ion batteries. The graphitized samples are labeled as A5,
B5, B8, and C15, respectively in this example. The test results
were listed in Table 6 below.
TABLE-US-00006 TABLE 6 Example Set 5 Initial Specific Coulombic
Graphite capacity efficiency sample (mAh/g) (%) All 348.2 94.4 B5
355.7 92.7 B8 356.2 93.6 C15 356.3 94.6
Comparative Example Set 1
[0042] The 5 .mu.m powder of coke A and the 5 and 8-micrometer
powders of coke B were graphitized in nitrogen gas environment
without any carbide forming elements under the same condition as
Example Set 4. The graphitized powders were evaluated as anode
material for lithium-ion batteries in the same way as the above
examples. These samples were labeled as A5, B5, and B8,
respectively in this example. The test results are also listed in
Table 7 under Comparative Example 1 below.
TABLE-US-00007 TABLE 7 Comparative Example Set 1 Initial Specific
Coulombic Graphite capacity efficiency sample (mAh/g) (%) A5 313.9
53.6 B5 312.5 41.7 B8 309.9 38.2
Comparative Example Set 2
[0043] The 5 and 8 micrometer powders of coke B were coated with 8
wt % and 6 wt % pitch using the solution phase precipitation method
as described in U.S. Pat. No. 7,323,120. The pitch coating process
involves several steps including a) dispersing the coke powder in
an organic solvent, b) dissolving the selected pitch in the organic
solvent, c) heating both the coke and pitch solution to an elevated
temperature, d) mixing the two solutions and cooling the mixture
under continuous agitation so that a certain heavy portion of the
dissolved pitch precipitates out as solid film on coke particles,
e) separating the pitch-coated coke particles from the solution by
filtration, f) washing out the residual pitch solution on the
coated coke particles using extra organic solvent and finally
drying the pitch-coated particles. The pitch-coated powders were
further processed by oxidation in air at an elevated temperature
(below 350.degree. C.) so that the resulting particles become
infusible and the coated pitch becomes less graphitizable than the
bulk coke core. This process is typically named as stabilization.
After pitch-coating and stabilization, the powders were graphitized
under the same condition as Example Set 4. The graphitized powders
were evaluated as anode material for lithium-ion batteries in the
same way as before and the results are posted in Table 8 under
Comparative Example 2 below.
TABLE-US-00008 TABLE 8 Comparative Example 2 Initial Specific
Coulombic Graphite capacity efficiency sample (mAh/g) (%) B5 325.4
95.0 B8 328.7 95.4
[0044] The Sample Sets 3 and 4 were subjected to analytical testing
to determine its constituents after graphitization. The amounts of
carbide and nitride forming elements in the anode material after
testing are shown in Table 9. Not all elements could be measured
considering the intrinsically low levels and the capabilities of
inhouse testing equipment.
TABLE-US-00009 TABLE 9 Example Set 3 Graphite Element content (ppm)
sample B Ce Mn Si Y A 1670 14.6 below Not Not B 493 3060 detectable
tested tested C 320 248 level (BDL) D 63.5 BDL E 72.9 F 12.2
Example Set 4 A 3060 165 below Not Not B 185 174 detectable tested
tested C 474 248 level (BDL) D 79.8 BDL E 51.1 F 8.36
[0045] In Sample Set 5, an anode sample was made with 8 .mu.m
premium coke by graphitizing in nitrogen gas at 2900 and for
fifteen minutes in a nitrogen environment, with a combination of
Boron and another Carbide or Nitride forming element at a ratio
1:3. The weights are measured before graphitization. The results
are shown in Table 10.
TABLE-US-00010 TABLE 10 Example Set 5 Initial Specific Coulombic
capacity efficiency Carbide Element (mAh/g) (%) B and Ce (0.5%,
1.5% by wt) 348.9 92.5 B and La (0.5%, 1.5% by wt) 343.9 92.6 B and
Mo (0.5%, 1.5% by wt) 332.5 93.1 B and Nb (0.5%, 1.5% by wt) 332.6
92.5 B and Ti (0.5%, 1.5% by wt) 349.2 93.4 B and F (0.5%, 1.5% by
wt) 334.4 92.1
[0046] The above examples demonstrate that the graphite powders
produced according to this invention exhibit superior specific
capacity and excellent initial coulombic efficiency compared to
those made through the state-of-art processes and that the process
is simple and the resulting graphite powders have different
chemical compositions on either particle surface or bulk from those
made with prior art processes.
[0047] In closing, it should be noted that the discussion of any
reference is not an admission that it is prior art to the present
invention, especially any reference that may have a publication
date after the priority date of this application. At the same time,
each and every claim below is hereby incorporated into this
detailed description or specification as an additional embodiment
of the present invention.
[0048] Although the systems and processes described herein have
been described in detail, it should be understood that various
changes, substitutions, and alterations can be made without
departing from the spirit and scope of the invention as defined by
the following claims. Those skilled in the art may be able to study
the preferred embodiments and identify other ways to practice the
invention that are not exactly as described herein. It is the
intent of the inventors that variations and equivalents of the
invention are within the scope of the claims while the description,
abstract and drawings are not to be used to limit the scope of the
invention. The invention is specifically intended to be as broad as
the claims below and their equivalents.
* * * * *