U.S. patent application number 14/083764 was filed with the patent office on 2014-07-03 for sulfur-infused carbon for secondary battery materials.
This patent application is currently assigned to NANOPARTICLE ORGANIC HYBRID MATERIALS (NOHMS). The applicant listed for this patent is Nanoparticle Organic Hybrid Materials (NOHMs). Invention is credited to Nathan BALL, Richard DELMERICO, Jonathan LEE, Surya S. MOGANTY, Jayaprakash NAVANEEDHAKRISHNAN.
Application Number | 20140186695 14/083764 |
Document ID | / |
Family ID | 50731841 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140186695 |
Kind Code |
A1 |
MOGANTY; Surya S. ; et
al. |
July 3, 2014 |
SULFUR-INFUSED CARBON FOR SECONDARY BATTERY MATERIALS
Abstract
In one aspect, a method of producing a sulfur-infused
carbonaceous material as a cathode material for use in a Li--S
battery is described, including providing a carbonaceous material;
mixing elemental sulfur with the carbonaceous material; and heating
the mixed sulfur and the carbonaceous material at a temperature
from about 445.degree. C. to about 1000.degree. C. for a period of
time and under a pressure greater than 1 atm to generate a sulfur
vapor to infuse the carbonaceous material to result in a
sulfur-infused carbonaceous material. In another aspect, a reactor
for producing a sulfur-infused carbonaceous material as a cathode
material for use in a Li--S battery is described, including a
reactor body capable of withstanding a pressure from about 1 atm to
about 150 atm; and an inner sulfur-resistant layer at the inner
surface of the reactor, wherein the inner layer is inert to sulfur
vapor at a temperature from about 450.degree. C. to about
1000.degree. C.
Inventors: |
MOGANTY; Surya S.;
(Henrietta, NY) ; NAVANEEDHAKRISHNAN; Jayaprakash;
(Lexington, KY) ; LEE; Jonathan; (Rochester,
NY) ; DELMERICO; Richard; (Henrietta, NY) ;
BALL; Nathan; (Lexington, KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanoparticle Organic Hybrid Materials (NOHMs) |
Ithaca |
NY |
US |
|
|
Assignee: |
NANOPARTICLE ORGANIC HYBRID
MATERIALS (NOHMS)
Ithaca
NY
|
Family ID: |
50731841 |
Appl. No.: |
14/083764 |
Filed: |
November 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61728002 |
Nov 19, 2012 |
|
|
|
61872300 |
Aug 30, 2013 |
|
|
|
Current U.S.
Class: |
429/188 ;
118/724; 427/113; 429/231.8 |
Current CPC
Class: |
B01J 19/02 20130101;
B01J 2219/0218 20130101; H01M 4/663 20130101; Y02T 10/70 20130101;
H01M 4/1397 20130101; H01M 10/052 20130101; H01M 4/0471 20130101;
Y02E 60/10 20130101; B01J 2219/029 20130101; B01J 2219/0209
20130101; B01J 2219/0236 20130101; Y02P 70/50 20151101; H01M 4/364
20130101; H01M 4/136 20130101; H01M 2004/021 20130101; H01M 4/583
20130101 |
Class at
Publication: |
429/188 ;
427/113; 118/724; 429/231.8 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/136 20060101 H01M004/136; H01M 4/04 20060101
H01M004/04 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made in part with government support
under Grant No. IIP-1142767, awarded by National Science Foundation
under a Small Business Innovation Research Phase I grant. The
United States government has certain rights in this invention.
Claims
1. A method of producing a sulfur-infused carbonaceous material as
a cathode material for use in a Li--S battery, comprising:
providing a carbonaceous material; mixing elemental sulfur with the
carbonaceous material; and heating the mixed sulfur and the
carbonaceous material at a temperature from about 445.degree. C. to
about 1000.degree. C. for a period of time and under a pressure
greater than 1 atm to generate a sulfur vapor to infuse the
carbonaceous material with sulfur to result in a sulfur-infused
carbonaceous material.
2. The method of claim 1, wherein the sulfur-infused carbonaceous
material comprises from about 10 wt % to about 99 wt % of sulfur
after a single heating operation.
3. The method of claim 1, wherein the sulfur-infused carbonaceous
material comprises more than 50 wt % of sulfur after a single
heating operation.
4. The method of claim 1, wherein the sulfur-infused carbon
comprises more than 60 wt % sulfur after a single heating
operation.
5. The method of claim 1, wherein the method further comprises
cooling the heated mixed sulfur and the carbonaceous material.
6. The method of claim 1, wherein the period is about 1 minute to
about 4 hours.
7. The method of claim 1, wherein the carbonaceous material is
selected from the group consisting of coal, polyacrylonitrile,
resorcinol-formaldehyde resins, KetJen, aerogel, coconut, bamboo,
plant derived carbon, CNT, graphene, acetylene black, Super P and a
combination thereof.
8. The method of claim 1, wherein providing a carbonaceous material
further comprises activating the carbonaceous material.
9. The method of claim 8, wherein activating the carbonaceous
material comprises using a base selected from the group consisting
of KOH, NaOH, LiOH, and combinations thereof.
10. The method of claim 9, wherein the activated carbonaceous
material has a surface area greater than about 1000 m.sup.2/g.
11. The method of claim 1, wherein the temperature is from
500.degree. C. to about 800.degree. C.
12. The method of claim 1, wherein the temperature is from
500.degree. C. to about 600.degree. C.
13. The method of claim 1, wherein the pressure is between about 2
atm to about 150 atm.
14. The method of claim 1, wherein the temperature is about
500.degree. C. to about 600.degree. C. and the pressure is about 2
atm to 3 atm.
15. The method of claim 1, wherein the temperature is about
700.degree. C. to about 800.degree. C. and the pressure is about 20
atm to 30 atm.
16. The method of claim 1, wherein the temperature is about
1000.degree. C. and the pressure is about 140 atm to 150 atm.
17. The method claim 1, wherein providing a carbonaceous material
comprises providing an activated coal.
18. The method of claim 17, wherein the activated coal has a heavy
metal ion impurity of less than 100 ppm and a surface area greater
than 1000 m.sup.2/g;
19. The method of claim 18, wherein providing an activated coal
comprises: purifying coal to contain less than 100 ppm of heavy ion
impurities; activating coal by heating a mixture of the purified
coal and a base; and sintering the activated coal at a temperature
in the range of 900.degree. C.-1300.degree. C. to provide an
activated coal having a surface area greater than 1000
m.sup.2/g.
20. The method of claim 19 wherein purification comprises: treating
coal with leaching solution containing acids, oxidizers, and water;
and washing the coal with water to remove impurities.
21. The method of claim 17, wherein the activation step comprises
heating to temperatures between 500 and 900.degree. C.
22. The method of claim 17, further comprising pulverizing the
coal.
23. The method of claim 22 further comprising heating to a
temperature of 900.degree. C. for 8 to 10 hours prior to
pulverizing.
24. The method of claim 19, wherein purifying coal comprises using
an acid selected from the group consisting of HCl, H.sub.2SO.sub.4,
HNO.sub.3, and combinations thereof.
25. The method of claim 19, wherein activating coal comprises using
a base selected from the group consisting of KOH, NaOH, LiOH, and
combinations thereof.
26. The method of claim 19, wherein sintering comprises using a gas
environment selected from the group consisting of N.sub.2,
CO.sub.2, Ar, He, H.sub.2, CO, NO.sub.x, and combinations
thereof.
27. The method of claim 19, comprising providing activated coal
having a surface area between 1000 and 2000 m.sup.2/g.
28. The method of claim 1, wherein providing a carbonaceous
material comprises providing activated carbonaceous material having
graphitic content between 1 and 20 mass %.
29. The method of claim 1, wherein providing a carbonaceous
material comprises providing activated carbonaceous material having
graphitic content between 5 and 10 mass %.
30. The method of claim 1, wherein the sulfur-infused carbon
comprises between 60 wt % and 95 wt % sulfur after in a single
heating operation.
31. A Li--S battery, comprising: a cathode comprising a coal-sulfur
composite, the composite comprising activated coal having a heavy
metal ion impurity of less than 100 ppm, a surface area greater
than 1000 m.sup.2/g and at least 60 wt % sulfur; an electrolyte;
and a lithium anode.
32. The battery of claim 31, wherein the electrolyte comprises a
thermally stable ionic liquid, lithium salt, and aprotic
solvent.
33. The battery of claim 31 comprising activated coal having a
surface area between 1000 and 2000 m.sup.2/g.
34. The battery of any of claims 31, comprising activated coal
having graphitic content between 1 and 20 mass %.
35. The battery of any of claims 34 comprising activated coal
having graphitic content between 5 and 10 mass %.
36. The battery of any one of claims 31, wherein initial battery
capacity is between 400 and 1200 mAh/g.
37. The battery of any one of claims 36, wherein initial battery
capacity is between 700 and 1000 mAh/g.
38. A reactor for producing a sulfur-infused carbonaceous material
as a cathode material for use in a Li--S battery, comprising: a
reactor body configured to withstand a pressure from about 1 atm to
about 150 atm; and an inner sulfur-resistant layer at the inner
surface of the reactor body, wherein the inner layer is inert to
sulfur vapor at a temperature from about 450.degree. C. to about
1000.degree. C.
39. The reactor of claim 38, wherein the reactor body and the inner
layer are made of the same material.
40. The reactor of claim 39, wherein the material withstands a
pressure from about 1 atm to about 150 atm and is layer is inert to
sulfur vapor at a temperature from about 450.degree. C. to about
1000.degree. C.
41. The reactor of claim 39, wherein the material is selected from
the group consisting of titanium, molybdenum, Tungsten and a
combination thereof.
42. The reactor of claim 38, wherein the reactor body and the inner
layer are made of different materials.
43. The reactor of claim 42, wherein the reactor body is made of a
material selected from the groups consisting of titanium,
molybdenum, Tungsten, stainless steel, and a combination
thereof.
44. The reactor of claim 42, wherein the inner layer is made of a
material selected from the group consisting of titanium,
molybdenum, Tungsten, quartz, alumina, silicon carbide, Nucerite
7040 (Pfaudler), Nitraglass 6510 (Pfaudler), SiO.sub.2, and a
combination thereof.
45. The reactor of claim 42, wherein the inner layer is a sheath or
liner configured to slide in and out of the reactor body.
46. The reactor of claim 42, wherein the inner layer is a coating
coated on the inner surface of the reactor body.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Application No. 61/728,002,
filed Nov. 19, 2012, and to Provisional Application No. 61/872,300,
filed Aug. 30, 2013, the contents of which are incorporated by
reference in their entirety.
INCORPORATION BY REFERENCE
[0003] All patents, patent applications and publications cited
herein are hereby incorporated by reference in their entirety. The
disclosures of these publications in their entireties are hereby
incorporated by reference into this application in order to more
fully describe the state of the art as known to those skilled
therein as of the date of the invention described herein.
TECHNICAL FIELD
[0004] Embodiments relate generally to sulfur containing activated
carbon and the use thereof as a cathode in a lithium ion secondary
cell.
BACKGROUND
[0005] Among cathode materials for secondary lithium batteries,
elemental sulfur has a very high theoretical capacity, 1672
mAhg.sup.-1 against lithium, which is considerably greater than
that of many commercially used transition metal phosphates and
transition metal oxides. In addition, elemental sulfur also
provides several other advantages as a cathode material for a
secondary lithium battery, including in particular a low cost and a
widespread availability. Sulfur has consequently been studied
extensively as a cathode material for secondary lithium batteries
and is considered a promising candidate for a cathode material for
secondary lithium batteries that may be used in electric and hybrid
electric vehicles.
[0006] Despite this promise, implementation of Li--S secondary
battery systems for high power applications has been problematic
for various reasons. For one, sulfur by itself has relatively low
electrical conductivity. Thus, desirable are methods and materials
that provide an opportunity to fully realize the advantages of
sulfur as a cathode material within a Li--S secondary battery
system.
[0007] Carbon, from sources such as coal, can be used to provide
conductivity to materials, and has been used in lithium ion
electrodes for this purpose.
[0008] While lithium sulfur (Li--S) cathode material has long
enjoyed a significant (10.times.) specific capacity advantage over
current lithium-ion batteries, Li--S chemistries have been
impractical due to poor cycle life and a high rate of discharge.
The polysulfide shuttling reaction between sulfur and its lithiated
compounds has limited the development of batteries based on the
Li--S chemistry because the reaction leads to irreversible material
losses in the battery that reduces energy storage capacity over
time. Shuttling is a cyclic process in which long-chain lithium
polysulfides, (Li.sub.2S.sub.n, 2<n<8), generated at the
cathode during charging, dissolve into the electrolyte and migrate
to the anode by diffusion where they react with the lithium
electrode in a parasitic fashion to generate lower-order
polysulfides, which diffuse back to the sulfur cathode and
regenerate the higher forms of polysulfide. Since this polysulfide
shuttling or dissolution takes place at the expense of the
available electroactive sulfur species, the reversibility of sulfur
and/or sulfide is broadly considered a major technical barrier
towards commercialization of high-energy Li--S batteries. Another
limitation is elemental sulfur is a poor electrical conductor (with
a conductivity.apprxeq.5.times.10.sup.-30 S cm.sup.-1 at 25.degree.
C.), which has limited the rate at which a conventional Li--S
battery can be discharged/charged.
[0009] Thus, there remains a need for sulfur-containing cathode
materials for lithium secondary cell with improved conductivity and
cycle life.
SUMMARY
[0010] Described herein are methods for producing sulfur-infused
carbonaceous material as a cathode material for use in a Li--S
battery. In some embodiments, elemental sulfur and a carbonaceous
material are premixed before heating and the mixed sulfur and the
carbonaceous material are heated to a temperature from about
445.degree. C. to about 1000.degree. C. for a period of time and
under a pressure greater than 1 atm to generate a sulfur vapor to
infuse the carbonaceous material with sulfur to result in a
sulfur-infused carbonaceous material. Because elemental sulfur and
the carbonaceous material are premixed, the elemental sulfur and
the carbonaceous material are heated to the same temperature. In
certain embodiments, the sulfur-infused carbonaceous material
produced using method as described herein comprises more than 50 wt
% of sulfur after a single heating operation.
[0011] In some embodiments, a low-cost, efficient method of
achieving sulfur-containing high-surface area, high-conductivity
carbon derived from bulk coal (i.e. activated carbon) for lithium
secondary cell applications is provided.
[0012] Sulfur containing carbon and methods of production thereof
from coal are described for lithium secondary cell applications.
The disclosure reports a high-energy density, low-cost rechargeable
lithium sulfur battery technology.
[0013] In one aspect, a method of producing an cathode material for
use in a Li--S battery includes providing activated coal having a
heavy metal ion impurity of less than 100 ppm and a surface area
greater than 1000 m.sup.2/g; mixing elemental sulfur with the
activated coal; and heating the mixed sulfur and activated coal to
infuse the coal with at least 60 wt % sulfur in a single heating
operation.
[0014] In one or more embodiments, providing activated coal
includes purifying coal to contain less than 100 ppm of heavy ion
impurities; activating coal by heating a mixture of the purified
coal and a base; and sintering the activated coal at a temperature
in there range of 900.degree. C.-1300.degree. C. to provide an
activated coal having a surface area greater than 1000
m.sup.2/g.
[0015] Also described herein are reactors for producing a
sulfur-infused carbonaceous material as a cathode material for use
in a Li--S battery, including a pressure-resistant reactor body and
an inner sulfur-resistant layer at the inner surface of the
reactor. Li--S batteries containing sulfur-infused carbonaceous
materials produced as described herein are also described. The
disclosure reports a high-energy density, low-cost rechargeable
lithium sulfur battery technology.
[0016] In one aspect, a method of producing a sulfur-infused
carbonaceous material as a cathode material for use in a Li--S
battery is described, including:
[0017] providing a carbonaceous material;
[0018] mixing elemental sulfur with the carbonaceous material;
and
[0019] heating the mixed sulfur and the carbonaceous material at a
temperature from about 445.degree. C. to about 1000.degree. C. for
a period of time and under a pressure greater than 1 atm to
generate a sulfur vapor to infuse the carbonaceous material with
sulfur to result in a sulfur-infused carbonaceous material.
[0020] In any one of the embodiments disclosed herein, the
sulfur-infused carbonaceous material includes from about 10 wt % to
about 99 wt % of sulfur after a single heating operation.
[0021] In any one of the embodiments disclosed herein, the
sulfur-infused carbonaceous material includes more than 50 wt % of
sulfur after a single heating operation.
[0022] In any one of the embodiments disclosed herein, the
sulfur-infused carbon includes more than 60 wt %, 65 wt %, 70 wt %,
75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt %, or 97 wt % of sulfur
after a single heating operation.
[0023] In any one of the embodiments disclosed herein, the method
further includes cooling the heated mixed sulfur and the
carbonaceous material.
[0024] In any one of the embodiments disclosed herein, the method
further includes cooling the heated mixed sulfur and the
carbonaceous material to room temperature.
[0025] In any one of the embodiments disclosed herein, the period
is about 1 minute, 10 minutes, 30 minutes, 1 h, 2 h, 3 h, or 4
h.
[0026] In any one of the embodiments disclosed herein, the
carbonaceous material is selected from the group consisting of
coal, polyacrylonitrile, resorcinol-formaldehyde resins, KetJen,
aerogel, coconut, bamboo, plant derived carbon, CNT, graphene,
acetylene black, Super P and a combination thereof.
[0027] In any one of the embodiments disclosed herein, providing a
carbonaceous material further includes activating the carbonaceous
material.
[0028] In any one of the embodiments disclosed herein, activating
the carbonaceous material includes using a base selected from the
group consisting of KOH, NaOH, LiOH, and combinations thereof.
[0029] In any one of the embodiments disclosed herein, the
activated carbonaceous material has a surface area greater than
about 1000 m.sup.2/g.
[0030] In any one of the embodiments disclosed herein, the
temperature is from about 450.degree. C. to about 900.degree. C.,
from about 500.degree. C. to about 800.degree. C., from about
500.degree. C. to about 700.degree. C., or from about 500.degree.
C. to about 600.degree. C.
[0031] In any one of the embodiments disclosed herein, the
temperature is about 550.degree. C.
[0032] In any one of the embodiments disclosed herein, the pressure
is about 2 atm, about 3 atm, about 5 atm; about 10 atm, about 20
atm, about 25 atm, about 50 atm, about 100 atm, or about 150
atm.
[0033] In any one of the embodiments disclosed herein, the
temperature is about 500.degree. C. and the pressure is about 2.05
atm.
[0034] In any one of the embodiments disclosed herein, the
temperature is about 750.degree. C. and the pressure is about 25.4
atm.
[0035] In any one of the embodiments disclosed herein, the
temperature is about 1000.degree. C. and the pressure is about
144.5 atm.
[0036] In any one of the embodiments disclosed herein, providing a
carbonaceous material includes providing and activating coal.
[0037] In any one of the embodiments disclosed herein, the
activated coal has a heavy metal ion impurity of less than 100 ppm
and a surface area greater than 1000 m.sup.2/g;
[0038] In any one of the embodiments disclosed herein, providing
and activating coal includes:
[0039] purifying coal to contain less than 100 ppm of heavy ion
impurities;
[0040] activating coal by heating a mixture of the purified coal
and a base; and
[0041] sintering the activated coal at a temperature in the range
of 900.degree. C.-1300.degree. C. to provide an activated coal
having a surface area greater than 1000 m.sup.2/g.
[0042] In any one of the embodiments disclosed herein, the
purification includes:
[0043] treating coal with leaching solution containing acids,
oxidizers, and water; and washing the coal with water to remove
impurities.
[0044] In any one of the embodiments disclosed herein, the
activation step comprises heating to temperatures between 500 and
900.degree. C.
[0045] In any one of the embodiments disclosed herein, the method
further includes pulverizing the coal.
[0046] In any one of the embodiments disclosed herein, the method
further includes heating to a temperature of 900.degree. C. for 8
to 10 hours prior to pulverizing.
[0047] In any of the preceding embodiments, heating the mixed
sulfur and activated coal includes heating to temperatures between
300.degree. C. and 1000.degree. C.
[0048] In any one of the embodiments disclosed herein, purifying
coal includes using an acid selected from the group consisting of
HCl, H.sub.2SO.sub.4, HNO.sub.3, and combinations thereof.
[0049] In any one of the embodiments disclosed herein, activating
coal includes using a base selected from the group consisting of
KOH, NaOH, LiOH, and combinations thereof.
[0050] In any one of the embodiments disclosed herein, sintering
includes using a gas environment selected from the group consisting
of N.sub.2, CO.sub.2, Ar, He, H.sub.2, CO, NO.sub.x, and
combinations thereof.
[0051] In any one of the embodiments disclosed herein, the method
includes providing activated coal having a surface area between
1000 and 2000 m.sup.2/g.
[0052] In any one of the embodiments disclosed herein, providing a
carbonaceous material includes providing activated carbonaceous
material having graphitic content between 1 and 20 mass %.
[0053] In any one of the embodiments disclosed herein, providing a
carbonaceous material comprises providing activated carbonaceous
material having graphitic content between 5 and 10 mass %.
[0054] In any one of the embodiments disclosed herein, the
sulfur-infused carbon includes 60 wt % and 95 wt % sulfur after in
a single heating operation.
[0055] In another aspect, a Li--S battery is described,
including:
[0056] a cathode comprising a sulfur-infused carbonaceous material
made by the method of any of the preceding embodiments;
[0057] an electrolyte; and
[0058] a lithium-containing anode.
[0059] In yet another aspect, a Li--S battery is described,
including:
[0060] a cathode comprising a coal-sulfur composite, the composite
comprising activated coal having a heavy metal ion impurity of less
than 100 ppm, a surface area greater than 1000 m.sup.2/g and at
least 60 wt % sulfur;
[0061] an electrolyte; and
[0062] a lithium anode.
[0063] In any one of the embodiments disclosed herein, the
electrolyte comprises a thermally stable ionic liquid, lithium
salt, and aprotic solvent.
[0064] In any one of the embodiments disclosed herein, the battery
includes activated coal having a surface area between 1000 and 2000
m.sup.2/g.
[0065] In any one of the embodiments disclosed herein, the battery
of any one of claims 32-35 wherein initial battery capacity is
between 400 and 1200 mAh/g.
[0066] In any one of the embodiments disclosed herein, the initial
battery capacity is between 700 and 1000 mAh/g.
[0067] In one or more embodiments, the battery including activated
coal having graphitic content between 1 and 20 mass %.
[0068] In one or more embodiments, the battery including activated
coal having graphitic content between 5 and 10 mass %.
[0069] In yet another aspect, a reactor for producing a
sulfur-infused carbonaceous material as a cathode material for use
in a Li--S battery is described, including:
[0070] a reactor body configured to withstand a pressure from about
1 atm to about 150 atm; and
[0071] an inner sulfur-resistant layer at the inner surface of the
reactor body, wherein the inner layer is inert to sulfur vapor at a
temperature from about 450.degree. C. to about 1000.degree. C.
[0072] In any one of the embodiments disclosed herein, the reactor
body and the inner layer are made of the same material.
[0073] In any one of the embodiments disclosed herein, the material
withstands a pressure from about 1 atm to about 150 atm and is
layer is inert to sulfur vapor at a temperature from about
450.degree. C. to about 1000.degree. C.
[0074] In any one of the embodiments disclosed herein, the material
is selected from the group consisting of titanium, molybdenum,
Tungsten and a combination thereof.
[0075] In any one of the embodiments disclosed herein, wherein the
reactor body and the inner layer are made of different
materials.
[0076] In any one of the embodiments disclosed herein, the reactor
body is made of a material selected from the groups consisting of
titanium, molybdenum, Tungsten, stainless steel, and a combination
thereof.
[0077] In any one of the embodiments disclosed herein, the inner
layer is made of a material selected from the group consisting of
titanium, molybdenum, Tungsten, quartz, alumina, silicon carbide,
Nucerite 7040 (Pfaudler), Nitraglass 6510 (Pfaudler), SiO.sub.2,
and a combination thereof.
[0078] In any one of the embodiments disclosed herein, the inner
layer is a sheath or liner configured to slide in and out of the
reactor body.
[0079] In any one of the embodiments disclosed herein, the inner
layer is a coating coated on the inner surface of the reactor
body.
[0080] It is contemplated that any embodiment disclosed herein may
be properly combined with any other embodiment disclosed herein.
The combination of any two or more embodiments disclosed herein is
expressly contemplated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0081] The invention is described with reference to the following
figures, which are presented for the purpose of illustration only
and are not intended to be limiting. In the Drawings:
[0082] FIG. 1 illustrates the weight percentages of sulfur
incorporated into coconut carbon under different heating time
analyzed by TGA experiments according to one or more
embodiments.
[0083] FIG. 2 illustrates the capacities of sulfur-infused KetJen
black materials produced under heating the sulfur at 165.degree.
C., 300.degree. C., and 550.degree. C.
[0084] FIG. 3 illustrates the capacities of sulfur-infused KetJen
black materials produced under heating the sulfur at 165.degree.
C., 300.degree. C., and 550.degree. C. after a plurality of
cycles.
[0085] FIG. 4 is a schematic of an exemplary set of steps involved
in synthesizing activated carbon from anthracite coal (i.e.
activated coal) according to one or more embodiments.
[0086] FIG. 5 is a drawing of an exemplary reactor for producing
sulfur-vapor-infused carbonaceous material according to one or more
embodiments.
[0087] FIG. 6a and FIG. 6b are schematics of exemplary reactors for
producing sulfur-vapor-infused carbonaceous material according to
one or more embodiments in which: FIG. 6 a) shows a reactor body
with a coated inner layer on its inside surface or the reactor body
and the inner layer forms the unitary body of the reactor; FIG. 6
b) shows a reactor body with a liner or a sheath.
[0088] FIG. 7 is a photograph of a sulfur infusion glass reactor
containing sulfur mixed activated coal according to one or more
embodiments.
[0089] FIG. 8 is a thermo gravimetric analysis plot showing sulfur
loading in the activated carbon derived from coal according to one
or more embodiments.
[0090] FIG. 9 is a plot of the cyclic voltammogram (CV) of
sulfur-infused activated carbon derived from coal according to one
or more embodiments.
[0091] FIG. 10 is a plot of the variation of discharge capacity as
a function of number of charge/discharge cycles according to one or
more embodiments.
[0092] FIG. 11 illustrates the XRD patterns of the activated carbon
(bottom) and sulfur infused activated carbon (top).
[0093] FIG. 12a) shows elemental composition of a representative
lab scale S@C composites analyzed by energy-dispersive X-ray (EDX)
microanalysis; FIG. 12b) shows the Thermo Gravimetric Analysis plot
for this S@C sample shown in FIG. 12a).
[0094] FIG. 13 shows a galvanostatic discharge coin cell test of
the lab scale material at 0.2 C for .about.150 cycles: (a) Voltage
vs. capacity (b) galvanostatic profile of Li--S@C battery under the
potential window 3.1-1.7 V and at 0.2 C rate (lab-scale
material).
[0095] FIG. 14 shows the powder XRD patterns of (a) activated
coconut carbon and (b) sulfur infused activated coconut carbon
using a large-scale reactor.
[0096] FIG. 15 shows the TEM images of the (a) activated commercial
coconut carbon and (b) after sulfur infusion.
[0097] FIG. 16 shows the nitrogen sorption isotherm of the
activated coconut carbon (a) before sulfur infusion and (b) after
sulfur infusion.
[0098] FIG. 17 shows the Thermo Gravimetric Analysis (TGA) recorded
for a S@C composite displaying the presence of 67% sulfur in the
composite.
[0099] FIG. 18 shows a typical cyclic voltammogram of S@C composite
according to one or more embodiments at a sweep rate 0.2 mV/s under
the potential window 1.7-2.8 V.
[0100] FIG. 19 shows: (a) Voltage vs. capacity profile and (b)
Cycle life behavior of Li--S battery assembled with a S@C composite
in Example 5 at 0.5 C current rate under the potential window
1.7-2.8V.
[0101] FIG. 20 shows the rate capability of a Li--S battery
according to one embodiment.
[0102] FIG. 21 shows the XRD patterns of (a) activated coconut
carbon and (b) sulfur infused activated coconut carbon using the
titanium reactor.
[0103] FIG. 22 shows the TEM images of the (a) activated commercial
coconut carbon and (b) after sulfur infusion in the titanium
reactor.
[0104] FIG. 23 shows the Thermo Gravimetric Analysis (TGA) recorded
for the S@C composite in Example 6 displaying the presence of 69%
sulfur in the composite.
[0105] FIG. 24 shows typical cyclic voltammogram of the S@C
composite in Example 6 at a sweep rate 0.2 mV/s under the potential
window 1.7-2.8 V.
[0106] FIG. 25 shows the electrochemical discharge and charge of
the titanium Li--S batteries at 0.2 and 1 C current rates: (a)
Voltage vs. capacity profile and (b) Cycle life behavior of Li--S
battery assembled with the S@C composite at 0.2 C and (c) 1 C
current rate under the potential window 1.7-2.8V. The capacity is
reported here in terms of the percentage (69%) of the sulfur active
mass.
DETAILED DESCRIPTION
[0107] Described herein are methods for producing sulfur-infused
carbonaceous material as a cathode material for use in a Li--S
battery and reactors for producing such sulfur-infused carbonaceous
material. Also described herein are high-energy density, low-cost
rechargeable lithium sulfur batteries including the sulfur-infused
carbonaceous materials.
Methods
[0108] In one aspect, a method for producing a sulfur-infused
carbonaceous material for use in Li--S batteries is described. In
some embodiments, a carbonaceous material is first provided and
then premixed with elemental sulfur. The carbonaceous material may
be selected from the group consisting of coal, polyacrylonitrile,
resorcinol-formaldehyde resins, KetJen, aerogel, coconut, bamboo,
plant derived carbon, CNT, araphene, acetylene black, Super P and a
combination thereof. Other carbonaceous materials known in the art
may also be used.
[0109] In some embodiments, elemental sulfur and a carbonaceous
material are premixed before heating. The mixed sulfur and the
carbonaceous material are then heated to the temperature in the
range of from about 445.degree. C. to about 1000.degree. C. for a
period of time and under a pressure greater than 1 atm to generate
a sulfur vapor. Because the element sulfur and the carbonaceous
material are mixed prior to heating, the element sulfur and the
carbonaceous material are naturally heated to the same temperature
to generate the sulfur vapor. In certain embodiments, the
temperature is from about 450.degree. C. to about 900.degree. C.,
from about 500.degree. C. to about 800.degree. C., from about
500.degree. C. to about 700.degree. C., or from about 500.degree.
C. to about 600.degree. C. In certain specific embodiments, the
temperature is about 550.degree. C.
[0110] In some embodiments, the method described herein is carried
out under the pressure of about 2 atm, about 3 atm, about 5 atm;
about 10 atm, about 20 atm, about 25 atm, about 50 atm, about 100
atm, or about 150 atm. In some embodiments, the pressure during the
sulfur-infusion is about 1 atm to about 2 atm, about 1 atm to about
5 atm, about 2 atm to about 3 atm, about 2 atm to about 5 atm,
about 1 atm to about 10 atm, about 1 atm to about 20 atm, about 1
atm to about 30 atm, about 1 atm to about 50 atm, about 1 atm to
about 100 atm, about 10 atm to about 20 atm, about 10 atm to about
30 atm, about 10 atm to about 40 atm, about 10 atm to about 50 atm,
about 10 atm to about 100 atm, about 20 atm to about 30 atm, about
20 atm to about 40 atm, about 20 atm to about 50 atm, about 20 atm
to about 100 atm, about 30 atm to about 40 atm, about 30 atm to
about 50 atm, about 30 atm to about 100 atm, about 40 atm to about
50 atm, about 40 atm to about 100 atm, or about 50 atm to about 100
atm. In some other embodiments, the pressure during the
sulfur-infusion is about 100 atm to about 150 atm. In some
embodiments, the pressure during the sulfur-infusion is determined
by the vapor pressure of the sulfur. In certain embodiments, the
method including heating the element sulfur at about 500.degree. C.
and the pressure under which the sulfur-infusion is carried out is
about 2.05 atm. In certain embodiments, the method including
heating the element sulfur at about 750.degree. C. and the pressure
under which the sulfur-infusion is carried out is about 25.4 atm.
In certain embodiments, the method including heating the element
sulfur at about 1000.degree. C. and the pressure under which the
sulfur-infusion is carried out is about 144.5 atm.
[0111] In certain embodiments, the mixture of element sulfur and
the carbonaceous material is heated for about 1 minute, 10 minutes,
30 minutes, 1 h, 2 h, 3 h, or 4 h. In certain embodiments, the
sulfur infusion can be achieved efficiently within minutes, e.g., 1
min or 10 mins and prolonged heating does not improve the weight of
sulfur incorporated into the carbon (FIG. 1). As FIG. 1
illustrates, premixed element sulfur and coconut were heated for 1
minute, 10 minutes, 30 minutes, 1 h, 1.5 h, or 4 h.
Thermogravametric analysis of the resulting product was conducted;
the weight loss is associates with the amount of sulfur in the
composite material due to the high volatility of sulfur. The TGA
analysis showed that in all cases the more than 60 wt % of sulfur
was incorporated into the carbonaceous material.
[0112] The carbonaceous material may be activated first to increase
its surface area carbonaceous material. In certain embodiments, the
carbonaceous material is treated with a base under heating to
activate the carbonaceous material. The base may be an inorganic
base selected from the group consisting of KOH, NaOH, LiOH, and a
combination thereof. In the activation step, the mixture of the
base and the carbonaceous material is heated to a temperature from
about 450.degree. C. to about 900.degree. C., from about
500.degree. C. to about 800.degree. C., from about 500.degree. C.
to about 700.degree. C., or from about 500.degree. C. to about
600.degree. C.
[0113] The process of activation may also further include purifying
the carbonaceous material and/or sintering the carbonaceous
material. The carbonaceous material may be washed with an acid to
remove impurities, e.g., heavy-metal ions. The acid may be selected
from the group consisting of HCl, H.sub.2SO.sub.4, HNO.sub.3, and
combinations thereof. In certain embodiments, after the
purification step, the heavy metal ion impurity in the carbonaceous
material is less than about 100 ppm, about 50 ppm, about 30 ppm,
about 20 ppm, or about 10 ppm.
[0114] The activated carbonaceous material may be further sintered
by a temperature in the range of 900.degree. C.-1300.degree. C. to
provide an activated carbonaceous material having a specific
surface area greater than about 1000 m.sup.2/g. In some
embodiments, the resulting activated carbonaceous material has a
specific surface area of greater than about 1000 m.sup.2/g, about
1100 m.sup.2/g, about 1200 m.sup.2/g, about 1300 m.sup.2/g, about
1400 m.sup.2/g, about 1500 m.sup.2/g, about 1600 m.sup.2/g, about
1700 m.sup.2/g, about 1800 m.sup.2/g, about 1900 m.sup.2/g, about
2000 m.sup.2/g, about 2100 m.sup.2/g, about 2200 m.sup.2/g, or
about 2500 m.sup.2/g. In certain embodiments, the resulting
activated carbonaceous material has a specific surface area between
about 1000 m.sup.2/g and about 2000 m.sup.2/g. In certain
embodiments, the activated carbonaceous material has a graphitic
content between 1 and 20 mass % or between 5 and 10 mass %.
[0115] The methods disclosed herein enable the production of
sulfur-vapor-infused carbonaceous material with high efficiency and
ease. First, unlike other methods known in the field which use low
temperature sulfur sublimation or liquid sulfur, the method
disclosed herein heat the sulfur above its boiling point to
generate sulfur vapor that can be infused rapidly and at high
sulfur content into the carbonaceous material. Applicants have
surprisingly found that when the sulfur vapor is used, the
resulting sulfur-infused carbonaceous material has superior
capacity and cyclability. As shown in FIGS. 2 and 3, KetJen black
material was infused with sulfur at three different heating
temperatures, e.g., 165.degree. C. (infusion with liquid sulfur),
300.degree. C. (infusion with liquid sulfur), and 550.degree. C.
(infusion with sulfur vapor). The results indicated that
sulfur-vapor infusion, i.e., when sulfur was heated to about
550.degree. C. (above its melting boiling point), the resulting
sulfur-vapor-infused KetJen black had the most capacity (FIG. 2).
Additionally, sulfur-vapor-infused KetJen black exhibited excellent
cyclability and maintained capacity superior to the KetJen black
with sulfur infused at 165.degree. C. or 300.degree. C. (FIG. 3).
These results indicate that vapor phase infusion is superior
compared to melt phase by allowing sulfur to penetrate into the
interiors of the meso-porous or nano-porous carbon matrix. Without
wishing to be bound by a particular theory, it is believed that in
the case of melt phase infusion (165 and 300.degree. C.), liquid
sulfur may not be able to penetrate deep into the carbon pores due
to the capillary forces. These results may be explained by the fact
that liquid sulfur viscosity decreases till 165.degree. C. and
increases rapidly with temperature due to polymerization of the
sulfur molecules. On the other hand, sulfur infusion above its
boiling point utilizes sulfur vapor to efficiently infuse the meso
or nano pores of the carbonaceous material and thus is
significantly more efficient.
[0116] Second, unlike other methods known in the field which
require the separation of the carbon and sulfur prior to heating,
the method disclosed herein allows the premix of element sulfur and
the carbonaceous material, thus reducing the complexity of the
operation. Additionally, other sulfur-vapor-infusion method known
in the field generally requires that the sulfur is heated,
separately from the carbon, to a temperature higher than the
temperature of the carbon to allow the sulfur to condense on the
cooler carbon. Applicants have surprisingly found that efficient
sulfur-infusion by sulfur vapor can be achieved by heating the
premixed sulfur and carbonaceous material to a common temperature
from about 445.degree. C. to about 1000.degree. C. followed by
cooling the mixture to allow sulfur to be infused into the
carbonaceous material. Without wishing to be bound to any
particular theory, it is believed that the affinity of carbon
towards sulfur contributes to the efficient sulfur incorporation
into the carbonaceous material in the methods as described
herein.
[0117] The method as disclosed herein results in highly efficient
sulfur incorporation where more than 50 wt % of
sulfur-incorporation is achieved after a single heating operation.
In some embodiments, more than 60 wt %, 65 wt %, 70 wt %, 75 wt %,
80 wt %, 85 wt %, 90 wt %, 95 wt %, or 97 wt % of
sulfur-incorporation is achieved after a single heating operation.
In some embodiments, about 66 wt % to about 70 wt % of
sulfur-incorporation is achieved after a single heating operation.
The wt % is measure by the percentage of sulfur weight of the total
weight of the sulfur-infused carbonaceous material.
[0118] In some embodiments, the carbonaceous materials are
developed from inexpensive and abundant feedstock. In certain
embodiments, the carbonaceous material is amorphous carbon such as
coal which can be processed into high surface area carbon through
pyrolysis and activation and finds its principal use in absorption
and filtration. Carbon in the form of crystalline graphite
possesses a combination of properties including lubricity,
refractoriness, chemical inertness, as well as thermal and
electrical conductivity. However, it is a challenge to obtain a
material having both high surface area and high graphitic content,
as would be required for use in batteries, as the high temperature
sintering processes used to enhance graphitic content tends to
reduce surface area.
[0119] Batteries, and in particular, lithium ion batteries are
sensitive to impurities. In particular, metallic ion impurities can
degrade the performance of the lithium ion batteries. Coal, having
metallic impurities and in particular heavy metal impurities is not
considered to be a suitable source for battery materials.
[0120] In one or more embodiments, the material is produced by
activating coal to create high surface area, high graphitic content
activated coal (i.e. activated carbon). In exemplary embodiments,
the activated coal has a surface area of greater than 1200
m.sup.2/g and a graphitic content of at least 10% by weight. In
addition, the metal ion impurities and in particular the heavy
metal ion impurities are typically less than 100 ppm.
[0121] A process for preparing a Li--S secondary battery from low
cost materials is described. The process includes providing a high
surface area, high graphitic content activated coal with a heavy
metals impurity content of typically less than 100 ppm and infusing
the activated coal with sulfur in a single step process. The
process thereby provides a material suitable for use in Li--S
batteries using low cost starting materials and minimal processing
steps.
[0122] A process for obtaining a high surface area, high graphitic
content activated coal with a heavy metals impurity content of
typically less than 100 ppm is described. Several steps are
involved in synthesizing activated carbon from anthracite coal.
Other coal sources can also be used (e.g., Lignite, bituminous,
subbituminous).
[0123] FIG. 4 describes a process 400 according to one or more
embodiments for obtaining a high surface, high graphitic content
carbon from coal. The process includes preheating of coal 402,
pulverization of preheated coal 404, leaching 406, washing and
filtration 408, activation 410, washing and filtration 412, and
sintering 414.
[0124] The coal is preheated prior to pulverization to reduce the
particle size. In certain embodiments the coal is preheated to a
temperature sufficient to reduce the mechanical strength of the
coal, which will in turn help to pulverize coal into desired mesh
size.
[0125] For example, the coal is heated to a temperature in the
range of 500 to 1500.degree. C.; and in one particular embodiment
can be heated to around 900.degree. C. The coal is typically heated
in an inert atmosphere for a time period in the range of 4 to 24
hrs. In certain embodiments, preheating is performed in a furnace
capable of maintaining inert atmosphere.
[0126] The pulverization step is accomplished using conventional
methods, such as ball milling. Grinding the coal serves to reduce
particle size and to expose and internal closed porosity generated
during the coal formation process.
[0127] In certain embodiments, the coal is typically reduced in
size to 300 mesh.
[0128] Once the coal has been pulverized, the coal powder is
treated to remove impurities that could interfere with battery
performance. In certain embodiments, the step of leaching 106
involves using strong acids such as HCl, H.sub.2SO.sub.4, and
HNO.sub.3 for purifying coal. Suitable leaching agents include
those capable of dissolving heavy metal ions, such as lead,
arsenic, selenium, cadmium, chromium, nickel and manganese that are
commonly found as impurities.
[0129] In other embodiments, the coal powder is treated with
oxidizing agents such as hydrogen peroxide. Not being bound by
theory, the purpose of oxidizing agent is to remove heavy metals
ions by forming water-soluble complexes.
[0130] Exemplary leaching conditions include dispersing pulverized
coal into water and mixing with leaching solution at room
temperature. The contents are typically stirred for 24 to 48
hrs.
[0131] After leaching to remove impurities, the coal is washed with
water to remove leaching agents and residual impurities. The coal
can be washed several times until no further impurities are
identified in the wash water.
[0132] The next step activates the coal and increases surface area.
In certain embodiments, the step of activation involves the use of
strong bases such as KOH, NaOH, and LiOH. Leached and dried coal is
mixed with a strong base and the heated at low temperatures in the
range of 450-900.degree. C. Typically the ratio of coal to base is
1:4 wt %. It is believed that the surface activation step proceeds
simultaneously with the chemical activation.
[0133] Once activated, the activated coal powders are sintered to
introduce a controlled graphitic content. In certain embodiments,
the sintering step (for carbonizing coal) is performed between
900.degree. C. and 2000.degree. C. Typical heating times varies
from 6 to 24 hrs. The use of this temperature range in the
sintering step allows for an increase of conductivity but does not
significantly reduce the material's surface area. In certain
embodiments, the sintering step is performed using two different
gas environments. In certain embodiments, the gas environment can
be a combination of any of N.sub.2, CO.sub.2, Ar, He, H.sub.2, CO,
or NOx. In some embodiments, inert environment is required to avoid
burning of coal at high sintering temperatures. A combination of
gases can also be used.
[0134] In other embodiments, carbonaceous materials other than coal
may also be subjected to similar purifying process, activation
process, and/or sintering process described above for coal.
[0135] Once the high surface area activated coal (or other
carbonaceous materials) has been obtained, it is infused with
sulfur in a process that provides at least 60 wt % sulfur loading
in a single step. In certain embodiments, gaseous sulfur is infused
into the activated coal material after activation. In certain
embodiments, elemental sulfur and activated coal are pre-mixed
prior to the infusion. In this case, pre-mixing is commonly
performed in a ball mill (typically for 30 min). While not being
bound by theory, it is believed that pre-mixing helps to form a
uniform sulfur carbon composite. In certain embodiments, this
infusion is performed under temperatures between 450 and
1000.degree. C. for 1 to 10 hrs, 1 to 4 hrs, or 1 to 2 hrs. In
certain embodiments, this infusion is performed under temperatures
between 450 and 1000.degree. C. for 1, 2, 10, 30, or 60
minutes.
[0136] In some embodiments, the sulfur infused activated coal
material (or other carbonaceous materials) has high surface area,
high conductivity (i.e., high graphitic content), and high sulfur
loading for improved lithium ion cathode performance. In some
embodiments, the surface area ranges from 100 to 2000 m.sup.2/g, or
preferably between 900 and 1200 m.sup.2/g. In some embodiments, the
graphitic content ranges between 1 and 20 mass %, or preferably
between 5 and 10 mass %. In some embodiments, the sulfur loading
ranges between 5 and 95% (of total weight), or preferably between
50 and 70% (of total weight). High surface area is important for
lithium ion diffusion, high conductivity is important for good
charge/discharge characteristics, and high sulfur loading is
important for charge capacity. In some embodiments, the capacity of
the cell ranges between 400 and 1200 mAh/g, or preferably between
700 and 1000 mAh/g.
Materials and Batteries
[0137] The sulfur-infused carbonaceous materials as disclosed
herein have high capacity and excellent cycle properties. As
described above, polysulfide shuttling and low electrical
conductivity of sulfur remain two main obstacles for the broad
application of Li--S batteries. Applicants have surprisingly found
that the sulfur-infused carbonaceous materials prepared accordingly
to methods disclosed herein possess high capacities and cyclability
when used in a Li--S battery. Without wishing to be bound by any
particular theory, it is believed that when sulfur is infused into
highly porous carbonaceous material, the porous carbon plays the
dual role of enhancing the overall conductivity of the composite
cathode as well as limiting polysulfide dissolution in the
electrolyte by trapping the lithium polysulfide from the
electrolyte. The methods of sulfur-vapor-infusion into carbon as
described herein enables significant sulfur incorporation into
carbon, e.g., more than 50 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt
%, 80 wt %, 85 wt %, 90 wt %, 95 wt %, or 97 wt % of sulfur, after
a single heating operation. The methods described herein maximizes
the amount of sulfur sequestered by the carbon pores and there by
minimizes lithium polysulfide dissolution/shuttling in the
electrolyte and finally facilitate good transport of electrons from
the poorly conducting sulfur.
[0138] The methods as described herein enable sequestering
vapor-infused sulfur into the carbonaceous materials' nano pores.
The nano pores have sizes less than 100 nm, 10 nm, 1 nm, 100 pm, or
10 pm. These pores simultaneously prevent dissolution and shuttling
of so-called long-chain lithium polysulfides, generated at the
cathode during charging, and facilitate transport of electrons into
and out of the cathode to improve conductivity. The former feature
makes it possible to retain high charge storage capacity over many
charge-discharge cycles, and the latter enhances charge/discharge
stability of the cell at much higher charge rates than previously
possible with a secondary Li--S battery. The nano pores sequester
and amorphize the sulfur, and act as mini reactors that constrain
reaction of lithium ions in solution and sulfur in the pores. The
resultant lithium sulfides (both soluble and insoluble
polysulfides) are also constrained by the pores, which, prevents
their loss to the electrolyte enhancing the reversibility of the
sulfur/sulfide reaction.
[0139] Accordingly, in some embodiments, sulfur-infused
carbonaceous materials produced using methods described herein have
an initial battery capacity between about 400 and about 1200 mAh/g,
when used in a Li--S battery. In some embodiments, the initial
battery capacity is between about 700 and about 1000 mAh/g, or 800
and about 900 mAh/g. In other embodiments, the initial battery
capacity is about 700, about 800, about 900, about 1000, about
1100, or about 1200 mAh/g.
[0140] In some embodiments, the sulfur-infused activated coal
material or other carbonaceous materials can be incorporated into
the cathode of a lithium secondary cell to produce a high energy
density, low-cost rechargeable battery with low-fade
charge-discharge characteristics. In some embodiments, the battery
consists of an anode, a cathode, and a separator disposed in
between. The cell geometry may be coin cell, prismatic, or
cylindrical cell. In some embodiments, lithium metal is used as the
anode.
[0141] In some embodiments, a hybrid electrolyte consisting of
thermally stable ionic liquid, lithium salt, a polymer and aprotic
solvents is used in the secondary cell. The ionic liquid may
contain an organic cation and inorganic/organic anion, with the
organic cation selected from a family of
N-alkyl-N-alkyl-pyrrolidinium, N-alkyl-N-alkyl-pyridinium,
N-alkyl-N-alkyl-imidazolium, N-alkyl-N-alkyl-phosphonium,
N-alkyl-N-alkyl-sulfonium, N-alkyl-N-alkyl-ammonium, and
N-alkyl-N-alkyl-piperdinium, and the anion selected from group of
tetrafluoroborate, hexafluorophosphate,
bis(trifluoromethylsulfonyl)imide,
bis(pentafluoroethylsulfonyl)imide, and trifluoroacetate. The
polymer in the electrolyte may include poly(ethylene glycol)
derivatives, with varying molecular weights ranging from 150 to
10000000 g/mol. The aprotic solvent may be selected from the group
consisting of carbonates, ethers, acetamides, acetontrile,
symmetric sulfones, 1,3-dioxolanes, dimethoxyethanes, glymes,
siloxanes and their blends. The lithium salt may be LiBF.sub.4,
LiNO.sub.3, LiPF.sub.6, LiAsF.sub.6, Lithium
bis(trifluoromethylsulfonyl)imide (LiTFSI), Lithium
bis(pentafluoroethylsulfonyl)imide, and Lithium
trifluoroacetate.
Reactors
[0142] In another aspect, a reactor for producing a sulfur-infused
carbonaceous material as a cathode material for use in a Li--S
battery is described. The reactor includes a pressure-resistant
reactor body configured to withstand a pressure up to about 150
atm; and an inner sulfur-resistant layer at the inner surface of
the reactor body, where the inner layer is inert to sulfur vapor at
the reaction temperature. In certain embodiments, the reaction
temperature is from about 450.degree. C. to about 1000.degree.
C.
[0143] In some embodiments, the reactor as disclosed herein is
described with references to FIGS. 5 and 6. FIG. 5 illustrates an
exemplary of a reactor disclosed herein. The reactor has a
tube-shaped reactor body 502 and metal flange 510 that is mated
with a cover plate 508 which seals the reactor during reaction. The
reactor also has one or more metal pins 504 to secure the flange
510 to the cover plate 508. The reactor may optionally contain
outlet 506 which may be used to insert a temperature or pressure
sensor to monitor the progress of the reaction.
[0144] FIG. 6 a) is a schematic drawing of an exemplary reactor 612
according to one or more embodiments for producing
sulfur-vapor-infused carbonaceous material. The reactor has a
reactor body 602 and an inner layer 604 at the inner surface of the
reactor. Because the sulfur-vapor-infusion occurs at high
temperature and under a pressure more than 1 atm within the reactor
chamber 610, the inner layer 604 needs to be made of a material
which is resistant to sulfur vapor under such conditions.
[0145] As described above, in certain embodiments, the temperature
for the sulfur-vapor-infusion is from about 450.degree. C. to about
900.degree. C., from about 500.degree. C. to about 800.degree. C.,
from about 500.degree. C. to about 700.degree. C., or from about
500.degree. C. to about 600.degree. C. Thus, in certain
embodiments, the inner layer 604 is made of a material selected
from the group consisting of titanium, molybdenum, Tungsten,
quartz, alumina, silicon carbide, Nucerite 7040 (Pfaudler),
Nitraglass 6510 (Pfaudler), SiO.sub.2, and a combination thereof.
Applicants have found that these materials are resistant to the
highly corrosive sulfur vapor at high temperature as described
above.
[0146] As described above, in certain specific embodiments, the
pressure under which the sulfur-vapor-infusion is carried out is
about 2 atm, about 3 atm, about 5 atm; about 10 atm, about 20 atm,
about 25 atm, about 50 atm, about 100 atm, or about 150 atm. Thus,
in certain embodiments, the reactor body 602 is made of a material
capable of withstanding such high pressure and is selected from the
group consisting of titanium, molybdenum, Tungsten, stainless
steel, and a combination thereof.
[0147] In certain embodiments, the reactor body 602 and the inner
layer 604 are made of the same material, which is both
sulfur-resistant under the reaction temperature and
pressure-resistant under the reaction pressure. Such material may
be selected from the group consisting of titanium, molybdenum,
Tungsten and a combination thereof. In these embodiments, the
reactor body 602 and the inner layer 604 together form a unitary
body of the reactor (FIG. 6a)) and there is no space between the
reactor body 602 and the inner layer 604.
[0148] In certain other embodiments, the reactor body 602 and the
inner layer 604 are made from different materials. In these
embodiments, the reactor body 602 may be made of a
pressure-resistant low-cost material such as stainless steel. Such
pressure-resistant low-cost material, e.g., stainless steel,
however, may be highly susceptible to sulfur-corrosion under
elevated temperatures such as those used in the methods described
herein. Applicants have found that a variety of stainless steel
alloys that were recommended by equipment manufacturers for use in
pressure vessels in sulfur containing environments are subjected to
significant sulfur corrosion under the sulfur-infusion conditions
described herein. These materials include: Haynes HR 160, Haynes HR
120, Haynes 25, Haynes 556, Haynes 282, Rolled Alloys 309H SS,
Rolled Alloys 310H SS, Rolled Alloys 253 MA, and Rolled Alloys 330
SS. However, these stainless steel materials may be used to
manufacture the reactor body of the reactor because its ability to
withstand high pressure, if a sulfur-resistant material as the
inner layer is used.
[0149] In certain such embodiments, the inner, sulfur-resistant
layer 604 may be a coating coated on the inner surface of the
reactor body 602. The coating may have a thickness of about 1
microns, 10 micros, 20 microns, 30 microns, 50 micros, or 100
microns. Such coating may be made of a sulfur-resistant material
selected from the group consisting of titanium, molybdenum,
Tungsten, quartz, alumina, silicon carbide, Nucerite 7040
(Pfaudler), Nitraglass 6510 (Pfaudler), SiO.sub.2, and a
combination thereof. The presence of such protective layer 604
prevents the pressure-resistant but sulfur-corrodible reactor body
602 made form materials such as stainless steel from reacting with
the sulfur vapor under the sulfur-infusion conditions. In these
embodiments, the inner layer 604 is coated on the inner surface 616
of the reactor body 602 as shown in FIG. 6a).
[0150] In certain other such embodiments, as shown in FIG. 6b), the
inner, sulfur-resistant layer 604' is a sheath or a liner which can
slide in and out of the reactor body 602'. In these embodiments,
the sheath or liner may be in any form factor as long as it
prevents sulfur vapor from leaking into the space 616' between the
reactor body 602' and the inner, sulfur-resistant layer 604'. In
some embodiments, the leaking is prevented by creating a pressure
tight seal so that the sulfur vapor cannot leak into the space
616'. In some specific embodiments, a gasket is used to seal the
top and bottom faces of the reactor 612' (not shown). In some
specific embodiments, the inner sheath or liner 604' may not be
pressure resistant and is subject to cracking under the high
pressure conditions described herein. In these embodiments,
counter-pressure with a gas may be applied in the space 616'
between the reactor body 602' and the sheath or liner 604',
equalizing pressure on both sides of the sheath or liner 604'wall
during operation.
[0151] The methods as described herein may be carried out in the
reactor 612 or 612'. As shown in FIG. 6a) or 6b), element sulfur
606 and carbonaceous material powders are premixed in reaction
chamber 610 or 610' and then the reactor can be subjected to
heating under the conditions as described above to infuse sulfur
into the carbonaceous material. After heating for the selected time
period described above at the temperature describe above, the
reactor is cooled to room temperature to produce the sulfur-infused
carbonaceous material.
[0152] The non-limiting embodiments are described in greater detail
in the following examples.
EXAMPLES
Characterization Techniques:
[0153] Surface analysis and phase purity measurements were carried
out on the carbon and S@C using Transmission electron microscopy
(TEM, Tecnai, T12, 120 kV) and powder X-ray diffraction (Scintage
X-ray diffractometer with Cu K.alpha. radiation). Percentage of
sulfur present in the S@C composite was calculated using
Thermogravimetric Analysis (under Ar, Thermo Scientific TA
Instrument (Nicolet iS10) operated at a heating rate of 20.degree.
C./min). Coin cells for electrochemical analysis were assembled
using the procedure mention under Section 2.2. Cyclic Voltammetry
and electrochemical charge discharge analysis were carried out
using Solartron's Cell Test model potentiostat (potential window
1.7-2.8 V at a scan rate of 0.2 mV/s) and MTI cycle life tester
(under the potential window 1.7-2.8V).
Example 1
Porous Carbon Synthesis/Activation and Sulfur Infusion
Procedure
[0154] Processes to use high surface area carbon from various
sources as the host for sulfur in Li--S@C batteries have been
developed. Specifically, Applicants have developed a high
temperature chemical as well as a physical methodology to activate
carbon, e.g., low cost carbon. Activation of the carbonaceous
material was carried out using KOH and high temperature. In a
process described herein, carbon was dispersed in tetrahydrofuran
(THF) then mixed with KOH and dried at medium temp for a few hours.
The dried carbon KOH mixture was heated at increasing temps in
N.sub.2 and then in a CO.sub.2 atmosphere. After the activation
process, the carbon KOH mixture was washed completely and heated
again to >1000.degree. C. to increase the graphitic content
(improve conductivity) in the carbon. These developments have
resulted in successful synthesis of high surface area, conductive
carbon nanostructures. Using this activated carbon, significant
sulfur infusion, e.g., more than 70 wt % sulfur has been
achieved.
Example 2
[0155] Coal was heated at 900.degree. C. for 8 to 10 hrs under
N.sub.2 atmosphere. This heat treatment helped to efficiently
pulverize coal in the next step. Preheated coal was pulverized
using a ball mall to 300 mesh size particles. The pulverized coal
particles were treated with leaching solution containing acids such
as, HNO.sub.3, HCl, etc, oxidizing agents such as H.sub.2O.sub.2
and water. This step was very critical in removing the impurities
such as heavy metal ions from the coal.
[0156] After leaching, coal was washed several times with water and
filtered. This step ensured that the unreacted leaching agents are
removed from the coal particles. This step was followed by
activation. Leached and dried coal was mixed with KOH at 1:4 weight
ratio and heated at 200.degree. C. for 2 hours. Then coal/KOH
mixture was heated at 500.degree. C. for 2 hr and 900.degree. C.
for 10 hr in N.sub.2 and for 2 hr in CO.sub.2 atmosphere. This
activation step increased the surface area and pore volume of the
coal particles.
[0157] After activation, coal was again washed several times with
water and filtered. This step ensured that the unreacted KOH was
removed from the coal particles. During the subsequent sintering
step, washed coal was heated at 1300.degree. C. under N.sub.2
atmosphere. This step increased the graphitic content and also
removed any remaining KOH.
[0158] The surface area of the resulting activated coal was 1450
m.sup.2/g and average pore size was 4 nm. Surface are and pore size
were determined using BET methods.
Example 3
[0159] Activated coal was produced as detailed in Example 2.
Elemental sulfur was infused into the activated coal in the vapor
form using the vacuum-sealed reactor shown in FIG. 7. 300 mg of
activated coal and 700 mg of elemental sulfur were mixed and
transferred into the glass reactor. The completely sealed reactor
was heated at 550-600.degree. C. for 4 to 6 hr. This method of
sulfur infusion facilitated fast, efficient, and controlled
infusion of elemental sulfur into the host activated coal. Thermo
Gravimetric Analysis (TGA) plot shown in FIG. 8 shows that about
67% of the mass of the sulfur infused activated coal (S@C)
composite was comprised of sulfur.
Example 4
[0160] The material of Example 3 was incorporated into the cathode
of a lithium ion secondary cell. A S@C cathode slurry was prepared,
by mixing 85% of the S@C composite and 7.5% of polyvinylidene
fluoride (PVDF) binder and 7.5% conducting activated coal (Super P)
in N-methyl pyrrolidine (NMP) solvent. Positive electrodes were
produced by coating this slurry on aluminum foil and drying at
90.degree. C. for 12 h. The resulting slurry-coated aluminum foil
was roll-pressed and the electrode was reduced to the required
dimensions with a punching machine. The electrode thickness of the
entire prepared electrodes was 80 .mu.m after 85% reduction of the
original thickness through the roll press.
[0161] Preliminary Li--S battery tests were conducted on 2032
coin-type cells, which were fabricated in an argon-filled glove box
using lithium metal anode and a microporous polyethylene separator.
The separator was interposed between the anode and cathode. The
electrolyte solution containing 0.5M lithium triflate and 0.1M
lithium nitrate in 5:3:2 volume ratio of tetraethylene glycol
dimethylether, 1,3-dioxolane and dimethoxyethane was used.
[0162] To characterize the oxidation/reduction behavior of sulfur
and polysulfides, slow scan cyclic voltammetry (CV) was carried out
using a Princeton Applied Research potentiostat. The CV sweeps were
performed on the S@C composite cathodes between 3 to 1.6 V using
0.2 mV/s scan rate. During the Li--S redox reaction,
electrochemical reduction of elemental sulfur occurs in two
different stages. In the first stage, sulfur reduces to higher
order polysulfides (Li.sub.2S.sub.n, 4<n<8) and further
reduction results in Li.sub.2S. Typically, the two distinct
reduction processes happen at .about.2.3V (vs Li/Li.sup.+) and at
.about.2.0 V (vs Li/Li.sup.+). Similarly, during the oxidation
process conversion of Li.sub.2S to elemental sulfur occurs at
.about.2.45 V. As shown in FIG. 9, the CV scans were repeated for
10 cycles and no significant changes were observed in the CV peak
positions or peak currents. These results suggest that the
combination of sulfur infused activated carbon derived from coal
and the electrolyte were effective in reducing polysulfide
dissolution (i.e., the dissolution of sulfur into the electrolyte).
While not being bound by theory, it is believed that the
combination of sequestered sulfur and electrolyte effectively
reduces the dissolution.
[0163] A galvanostatic charge and discharge test was performed to
investigate the changes of the electrochemical properties of the
Li--S battery with the synthesized S@C composite cathode under the
cell voltage of 3.0-1.7 V at a current rate of 0.2 C-rate. FIG. 10
depicts the capacity vs. cycle plots of the Li--S@C batteries at
room temperature. A very high initial capacity was observed and
gradually, the capacity decreased and remained constant for 100
cycles. At the end of 100 cycles, activated carbon derived from
coal showed specific capacity of 550 mAh/g. The capacity was
reported here in terms of the percentage (67%) of the sulfur active
mass. Even at a lower than initial capacity, the energy density of
the Li--S cell based on the activated carbon derived from coal was
>1000 Wh/kg, which is significantly higher than the energy
density of the state of the art Li-ion batteries.
Example 5
Characterization of the Produced Sulfur-Infused Carbonaceous
Material (S@C)
[0164] The following physical and electrochemical properties are
obtained for both Li--S cells made of sulfur infused carbon
composite (lab-scale) and S@C made in the large scale reactors. The
large scale reactor in this example was made from quartz and placed
within a furnace to heat the reactor. Quartz was found to be
resistant to sulfur corrosion. In a separate embodiment, the quartz
material was used to make a sheath or liner to be included in a
reactor body made from pressure-resistant stainless steel. The
sulfur-infusion occurred within the quartz sheath. The
pressure-resistant reactor body was physically separated from the
sulfur-containing quartz chamber, allowing stainless steel alloy to
be used. Counter-pressure with a gas is applied between the quartz
tube and the steel reactor body, equalizing pressure on both sides
of the quartz tube's wall during operation.
Sulfur Infused into Lab Scale Carbon Composite:
[0165] To check the microstructure and the graphitic character of
the activated carbon before and after sulfur infusion, the
materials were characterized by powder XRD (X-ray diffraction).
FIG. 10 shows a typical powder XRD patterns of the carbon before
and after sulfur infusion, which exhibits peaks at
2.theta..about.28 and 45.degree. that can respectively, be ascribed
to (002) and (101) planes associated with the graphitic pore walls.
No apparent peak due to sulfur was noticed in the powder XRD
pattern of the S@C composite. This indicates that the infused
sulfur exists in fine particles and in a highly dispersed state,
with the crystalline elemental sulfur most likely converted to
amorphous phase after heat treatment. FIG. 11 illustrated the XRD
patterns of the activated carbon (bottom) and sulfur infused
activated carbon (top). The XRD clearly show that the activated
carbon possesses partially graphitic (crystalline) behavior.
[0166] Elemental composition of a representative lab scale S@C
composites analyzed by energy-dispersive X-ray (EDX) microanalysis
is shown in FIG. 12a. An EDX spectrum collected from different
locations within the S@C material confirms the presence of sulfur
throughout the composite. Thermo Gravimetric Analysis plot for this
S@C sample shown in FIG. 12b illuminates nearly 61% of the mass of
the S@C composite is comprised of sulfur. FIG. 13 shows a
galvanostatic discharge coin cell test of the lab scale material at
0.2 C for .about.150 cycles. FIG. 13a) shows a Voltage vs. capacity
property of the material and FIG. 13b) shows a galvanostatic
profile of Li--S@C battery under the potential window 3.1-1.7 V and
at 0.2 C rate (lab-scale material).
Physical and Electrochemical Properties of S@C Composite Produced
Using a Reactor
[0167] The physical and electrochemical data reported for the Li--S
batteries assembled using the S@C cathode produced by the
large-scale reactor from commercially available activated coconut
carbon. FIG. 14 shows the powder XRD patterns of the large-scale
carbon before and after sulfur infusion using large scale reactor,
which exhibits peaks at 2.theta..about.28 and 45.degree. that can
respectively, be ascribed to (002) and (101) planes associated with
the graphitic pore walls. No apparent peak due to sulfur was
noticed in the powder XRD pattern of the S@C composite. This
indicates that the infused sulfur exists in fine particles and in a
highly dispersed state, with the crystalline elemental sulfur most
likely converted to amorphous phase after heat treatment.
Specifically, FIG. 14 illustrates the XRD patterns of a) activated
coconut carbon and b) sulfur infused activated coconut carbon using
a large-scale reactor.
[0168] FIGS. 15a)-b) shows Transmission Electron Microscopy of the
coconut carbon before and after sulfur infusion. There is not much
difference in the TEM pattern of activated coconut carbon. However,
the highly porous nature of the activated coconut carbon is clearly
visible from the TEM images obtained.
[0169] FIGS. 16a)-b) represents the BET surface area analysis of
the activated coconut carbon before and after sulfur infusion. As
expected, the surface area of the coconut carbon was reduced after
sulfur infusion, which, can be corroborated to the infusion of
sulfur in the minute pores of carbon matrix. That is, the surface
area of the activated carbon was found to be 2169 m.sup.2/g with 4
nm pore size and a pore volume of 1.4 cm.sup.3/g. Upon sulfur
infusion the surface area of the activated carbon was found to be
133 m.sup.2/g with a pore size of 4 nm in diameter and a pore
volume of 0.2 cm.sup.3/g. It is also interesting to note that the
nature of the BET isotherm changed upon infusing sulfur into
activated coconut carbon. This may be attributed to the change in
the physical and chemical nature of the coconut carbon upon sulfur
infusion. Thermo Gravimetric Analysis plot shown in FIG. 17
illuminates nearly 67% of the mass of the S@C composite is
comprised of sulfur.
[0170] FIG. 18 shows the cyclic voltammogram (CV) of the S@C
composite studied in the potential range of 1.7-2.8 V vs.
Li/Li.sup.+ at a scan rate of 0.2 mV/s. The voltammogram obtained
was similar to that of the pattern reported for Li--S batteries
with aerogel carbon based sulfur composite (lab-scale). The CV
pattern of the synthesized S@C composite exhibited a pair of
cathodic peaks at .about.2.4 and .about.1.9 V and a corresponding
pair of anodic peaks at .about.2.35 and 2.45 V. The first peak at
2.4 V involves the reduction of elemental sulfur to lithium
polysulfide (Li.sub.2S.sub.n, 4<n<8). The second peak at 1.9
V involves the reduction of sulfur in lithium polysulfide to
Li.sub.2S.sub.2 and eventually to Li.sub.2S. The anodic process
also occurs in two stages. The anodic peak at 2.35 V is associated
with the formation of Li.sub.2S.sub.n (n>2). This process
continues until lithium polysulfide is completely consumed and
elemental sulfur produced at 2.45 V.
[0171] FIG. 18 shows: (a) Voltage vs. capacity profile and (b)
Cycle life behavior of Li--S battery assembled with the S@C
composite in Example 5 at 0.5 C current rate under the potential
window 1.7-2.8V. The capacity is reported here in terms of the
percentage (67%) of the sulfur active mass.
[0172] The galvanostatic charge and discharge test is performed in
order to investigate the changes of the electrochemical properties
of the Li--S battery with the synthesized S@C composite cathode
under the cell voltage of 1.7-2.8 V at 0.5 C current rate. FIG. 19a
displays the voltage vs. capacity plots of the Li--S battery at
room temperature. An initial discharge capacity of 820 mAh/g was
observed with the discharge/charge plateaus reflecting the
reversible formation of various products starting from the
elemental sulfur to Li.sub.2S. The cycle life plot of the Li--S
battery for 300 cycles containing is shown in FIG. 19b. Excellent
cycling stability in addition to enhanced columbic efficiency is
observed from first to 300.sup.th cycle. Herein, the current rate
is based on the theoretical capacity of sulfur and the capacity is
reported in terms of the percentage of the sulfur active mass
present in the S@C composite, which is 67%. Even with this
capacity, the energy density of the Li--C@S battery is >600
Wh/kg, which is significantly higher than the energy density of the
state of the art Li-ion batteries. As mentioned earlier, this
excellent electrochemical stability of the S@C composite can be
attributed to the carbon used as the host structure for sulfur
infusion.
[0173] FIG. 20 shows the rate capability of a Li--S battery
according to one embodiment of the invention. Cycle life was
carried out at a constant. Rate capability study was carried out at
various current rates calculated based on the percentage of sulfur
active mass (67%) present in the cathode composite. The rate
capability behavior of the Li--S battery at higher rates is shown
in FIG. 20. At the maximum discharge rate studied, 1 C, the Li--S
battery is seen to deliver 410 mAh/g. The stability of the cathode
material is also evidenced by the recovery of a capacity of 720
mAh/g at 0.2 C rate following charging at the rather high rate of 1
C.
Example 6
Physical and Electrochemical Properties of S@C Composite Produced
Using a Titanium Reactor
[0174] In this example, a tube-shaped reactor body was made of
titanium alloy which is capable of withstanding sulfur atmosphere
and pressure. The reactor design is very simple but effective for
infusing sulfur into porous carbon structures at high temperature.
A normal tube furnace was used to heat the reactor for sulfur
infusion. A particular furnace was designed for this purpose to
ensure maximum heating and contact with the reactor. This titanium
alloy reactor was found to be capable of processing .about.200-500
g of S@C composite.
[0175] To check the microstructure and the graphitic character of
the activated coconut carbon before and after sulfur infusion using
this large scale reactor, the materials were characterized by
powder XRD. FIG. 20 shows the powder XRD patterns of the carbon
before and after sulfur infusion, which exhibits peaks at
2.theta..about.28 and 45.degree. that can respectively, be ascribed
to (002) and (101) planes associated with the graphitic pore walls.
No apparent peak due to sulfur was noticed in the powder XRD
pattern of the S@C composite. This is very similar to the XRD of
the infused material in Example 5.
[0176] FIGS. 22a)-b) show Transmission Electron Microscopy of the
coconut carbon before and after sulfur infusion in the titanium
Reactor. The highly porous nature of the activated coconut carbon
is clearly visible from the TEM images obtained. Thermo Gravimetric
Analysis plot shown in FIG. 23 illuminates nearly 69% of the mass
of the S@C composite is comprised of sulfur, indicating high
efficiency for infusing sulfur.
[0177] FIG. 24 shows the cyclic voltammogram (CV) of the titanium
reactor S @ C composite studied in the potential range of 1.7-2.8 V
vs. Li/Li.sup.+ at a scan rate of 0.2 mV/s. The voltammogram
obtained was similar to that of the pattern reported for Li--S
batteries with the lab based composite as well as the reactor in
Example 5. The CV pattern of the synthesized S@C composite exhibit
a pair of cathodic peaks at .about.2.4 and .about.1.9 V and a
corresponding pair of anodic peaks at .about.2.35 and 2.45 V.
[0178] FIG. 25a-c shows the electrochemical discharge and charge of
the titanium Li--S batteries at 0.2 and 1 C current rates. FIG. 25a
shows typical discharge/charge voltage profiles for the S@C
composite which exactly resemble the redox peaks observed in the CV
scans. As shown in FIG. 25b, the Li--S battery manifest an initial
specific discharge capacity of 1270 mAh/g (after the formation
cycle) and maintains a reversible capacity of 970 mAh/g (at a rate
of 0.2 C) with 93% capacity retention after 200 cycles. At 1C
current rate (FIG. 25c), the titanium Li--S battery has exhibited
an initial discharge capacity of 1150 mAh/g which has been
maintained at 610 mAh/g with a columbic efficiency of 93-98% at the
end of 200 cycles. Herein, the current rate is based on the
theoretical capacity of sulfur and the capacity is reported in
terms of the percentage of the sulfur active mass present in the
S@C composite, which is 69%.
[0179] The energy density of the Li--S@C battery is >800 Wh/kg,
which is significantly higher than the energy density of the state
of the art Li-ion batteries. As mentioned earlier, this excellent
electrochemical stability of the S@C composite can be attributed to
the carbon used as the host structure for sulfur infusion.
[0180] It will be appreciated that while a particular sequence of
steps has been shown and described for purposes of explanation, the
sequence may be varied in certain respects, or the steps may be
combined, while still obtaining the desired configuration.
Additionally, modifications to the disclosed embodiment and the
invention as claimed are possible and within the scope of this
disclosed invention.
* * * * *