Note: Descriptions are shown in the official language in which they were submitted.
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BATTERY BASED ON ORGANOSULFUR SPECIES
Field of the Invention
The invention relates to batteries having an anode based on sodium, lithium,
potassium, magnesium or a mixture thereof or alloy or composite of sodium,
lithium,
potassium and/or magnesium with one or more other metals and a cathode based
on
elemental sulfur, selenium, or mixture of elemental chalcogens, the anode and
cathode
being separated by a separator element with a liquid or gel electrolyte
solution of a
conductive salt in a nonaqueous polar aprotic solvent or polymer in contact
with the
electrodes.
Background of the Invention
Electrochemical batteries are a principal means for storing and delivering
electrical energy. Due to increasing demands for energy for electronic,
transportation
and grid-storage applications, the need for batteries with ever more power
storage and
delivery capability will continue long into the future.
Because of their light weight and high energy storage capacity as compared to
other types of batteries, lithium ion batteries have been widely used since
the early
1990's for portable electronic applications. However, current Li-ion battery
technology does not meet the high power and energy needs for large
applications such
as grid storage or electric vehicles with driving ranges that are competitive
with
vehicles powered by internal combustion engines. Thus, extensive efforts in
the
scientific and technical communities continue to identify batteries with
higher energy
density and capacity.
Sodium-sulfur and lithium-sulfur electrochemical cells offer even higher
theoretical energy capacity than Li-ion cells and thus have continued to
elicit interest
as "next-generation" battery systems. Electrochemical conversion of elemental
sulfur
to the monomeric sulfide (S2-) offers a theoretical capacity of 1675 mAh/g as
compared to less than 300 mAh/g for Li-ion cells.
Sodium-sulfur batteries have been developed and launched as commercial
systems. Unfortunately, the sodium-sulfur cell typically requires high
temperatures
(above 300 C) to be functional, and thus is only suitable for large stationary
applications.
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Lithium-sulfur electrochemical cells, initially proposed in the late 1950's
and
1960's, are only now being developed as commercial battery systems. These
cells
offer theoretical specific energy densities above 2500 Wh/kg (2800 Wh/L) vs.
624
Wh/g for lithium ion. The demonstrated specific energy densities for Li-S
cells are in
the range of 250-350 Wh/kg, as compared to 100 Wh/g for Li-ion cells, the
lower
values being the result of specific features of the electrochemical processes
for these
systems during charge and discharge. Given that the practical specific
energies of
lithium batteries are typically 25-35% of the theoretical value, the optimum
practical
specific energy for a Li-S system would be around 780 Whig (30% theoretical).
[V.S.
Kolosnitsyn, E. Karaseva, US Patent Application 2008/0100624 Al]
The lithium-sulfur chemistry offers a number of technical challenges that have
hindered the development of these electrochemical cells, particularly poor
discharge-
charge cyclability. Nonetheless, because of the inherent low weight, low cost,
high
power capacity of the lithium-sulfur cell, great interest exists in improving
the
performance of the lithium-sulfur system and extensive work has been performed
in
the last 20 years by many researchers all over the world to address these
issues. [C.
Liang, etal. in Handbook of Battery Materials 2nd Ed., Chapter 14, pp. 811-840
(2011); V.S. Kolosnitsyn, etal., J Power Sources 2011, 196, 1478-82; and
references
therein.]
A cell design for a lithium-sulfur system typically includes:
* An anode consisting of lithium metal, lithium-alloy or lithium-containing
composite materials.
=* A non-reactive but porous separator between the anode and cathode (often
polypropylene or a-alumina). The presence of this separator results in
separate
anolyte and catholyte compartments.
= A porous sulfur-bearing cathode that incorporates a binder (often
polyvinylidene
difluoride) and a conductivity-enhancing material (often graphite, mesoporous
graphite, multiwall carbon nanotubes, graphene),
= An electrolyte consisting of a polar aprotic solvent and one or more
conductive Li
salts [(CF3S02)2N-, CF3S03-, CH3S03-, C104-, PF6-, AsF6-, halogens, etc.].
The solvents used in these cells have included basic (cation-complexing)
aprotic
polar solvents such as sulfolane, dimethyl sulfoxide, dimethylacetamide,
tetmmethyl urea, N-methyl pyrrolidinone, tetraethyl sulfamide,
tetrahydrofuran,
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methyl-THF, 1,3-dioxolane, diglyme, and tetraglyme. Lower polarity solvents
are
not suitable due to poor conductivity and poor ability to solvate Li +
species, and
protic solvents can react with Li metal. In solid-state versions of the
lithium-
sulfur cell, the liquid solvents are replaced with a polymeric material such
as
polyethylene oxide.
= Current collectors and appropriate casing materials.
Summary of the Invention
Compositions and applications of organic polysulfides, organic thiolates and
organic polythiolates for use in metal-sulfur batteries, particularly lithium-
sulfur
batteries, are provided by the present invention. The organic polysulfide,
organic
thiolate and organopolythiolate species (hereinafter sometimes referred to as
"organosulfur species") act to improve the performance of such electrochemical
cells
during repealed discharge and charge cycles.
= The present invention thus relates to chemical sources of energy
comprising a
cell or battery with one or more positive electrodes (cathodes), one or more
negative
electrodes (anodes) and an electrolyte media, wherein the operative chemistry
involves reduction of sulfur or polysulfide species and oxidation of the
reactive metal
species. The negative electrode comprises a reactive metal such as lithium,
sodium,
potassium, magnesium or alloys/composites of those metals with other
materials; in
certain embodiments the negative electrode additionally comprises at least one
organosulfur species and/or has been treated with at least one organosulfur
species.
The positive electrode comprises elemental sulfur and/or selenium and, in
certain
embodiments of the invention, organosulfur species such as organic polysulfide
species and/or metal organic polysulfide salts, and matrices containing these
species.
The electrolyte matrices, in certain embodiments, comprise mixtures of organic
solvent or polymers, inorganic or organic polysulfide species, carriers for
the ionic
form of the active metal, and other components intended to optimize
electrochemical
performance.
Specifically, this invention relates to the use of organic sulfides and
polysulfides, and their lithium (or sodium, potassium, magnesium, quaternary
ammonium or quaternary phosphonium) organothiolate or organopolythiolate
analogs, as components in the cathode and electrolyte matrices. Said
organosulfur
species chemically combine with sulfur and anionic mono- or polysulfide
species to
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form organopolythiolate species which have increased affinity for the nonpolar
sulfur
components of the positive cathode and catholyte phase. The organosulfur
species is
also capable of reacting with the reactive metal or metals present in the
negative
electrode, to form metal salts of the organosulfur species on the surface of
the
negative electrode which help to enhance the performance of an electrochemical
cell
containing such organosulfur species-treated negative electrodes. Without
wishing to
be bound by theory, it is believed that the organosulfur species chemically
combine
with the reactive metal(s) of the anode and prevent the buildup of LiS2 on the
anode
as a result of a reaction between dissolved Li2Sn (n>1) species often present
in the
electrolyte solutions used in metal sulfur batteries. Accordingly, the
presence of
organosulfur species or the treatment of an anode with organosulfur species
may help
to prevent the translational flow of sulfur atoms or anions from the cathode
to the
anode by forming a protective layer on the anode surface which is capable of
conducting metal cations. The electrolyte becomes saturated in metal
polysulfide
species, resulting in less sulfur loss from the cathode, higher battery
capacities, and
increased total cycling life for the battery.
One aspect of the invention provides a battery, the battery comprising:
a) an anode comprising an anode active material comprising sodium, lithium,
potassium, magnesium or an alloy or composite of at least one of sodium,
lithium, potassium or magnesium with at least one other metal for
providing ions;
b) a cathode comprising a cathode active material comprising elemental
sulfur, elemental selenium or a mixture of elemental chalcogens; and
c) an intermediate separator element positioned between the anode and
cathode acting to separate liquid or gel electrolyte solutions in contact with
the anode and cathode, through which metal ions and their counterions
move between the anode and cathode during charge and discharge cycles
of the battery;
wherein the liquid or gel electrolyte solutions comprise a nonaqueous polar
aprotic solvent or polymer and a conductive salt and at least one of
conditions
(i), (ii), (iii) or (iv) is met:
(i) at least one of the liquid or gel electrolyte solutions
additionally
comprise at least one organosulfur species;
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(ii) the cathode is additionally comprised of at least one organosulfur
species;
(iii) the intermediate separator element comprises a functionalized porous
polymer containing at least one organosulfur species;
(iv) the anode is additionally comprised of or has been treated with at
least
one organosulfur species;
wherein the organosulfur species comprises at least one organic moiety and at
least one ¨S-Se- linkage, with n being 0 or an integer of 1 or more.
In one embodiment, just one of conditions (i), (ii), (iii) or (iv) is met. In
another embodiment, all four conditions are met. In still another embodiment,
only
two or three of the conditions are met, e.g., (i) and (ii), (i) and (iii),
(ii) and (iii), (i),
(ii) and (iii), (ii), (iii) and (iv), (i), (iii) and (iv), or (i), (ii) and
(iv).
In another aspect, the invention provides an electrolyte comprising at least
one
nonaqueous polar aprotic solvent or polymer, at least one conductive salt, and
at least
one organosulfur species comprised of at least one organic moiety and at least
one ¨S-
S.- linkage wherein n is an integer of I or more.
Another aspect of the invention provides a cathode comprising a) elemental
sulfur, elemental selenium or a mixture of elemental chalcogens, b) at least
one
electrically conductive additive, c) and at least one organosulfur species
comprising at
least one organic moiety and at least one ¨S-S.- linkage, n being 0 or an
integer of 1
Or more.
A further aspect of the invention provides an anode comprising an anode
active material comprising sodium, lithium, potassium, magnesium or an alloy
or
composite of at least one of sodium, lithium, potassium or magnesium with at
least
one other metal for providing ions, wherein the anode additionally comprises
or has
been treated with at least one organosulfur species comprising at least one
organic
moiety and at least one ¨S-Sn- linkage, n being 0 or an integer of 1 or more.
Such
treatment results in increased battery life and reduced capacity fade on
subsequent
cycles.
The organosulfur species, for example, may be selected from the group
consisting of organic polysulfides, organic thiolates (where n =0,
corresponding for
example to the general formula R-S-M, where R is an organic moiety and M is a
cation such as Li, Na, K, Mg, quaternary ammonium, or quaternary phosphonium)
and/or metal organic polythiolates. In certain embodiments of the invention,
the
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organosulfur species contains one or more sulfur-containing functional groups
selected from the group consisting of dithioacetal, dithioketal, trithio-
orthocarbonate,
thiosulfonate [-S(0)2-S-], thiosulfinate [-S(0)-S-], thiocarboxylate [-C(0)-S-
],
dithiocarboxylate [-C(S)-S-], thiophosphate, thiophosphonate,
monothiocarbonate,
.. dithiocarbonate,and trithiocarbonate. In other embodiments, the
organosulfiir species
may be selected from the group consisting of aromatic polysulfides, polyether-
polysulfides, polysulfide-acid salts and mixtures thereof.
Brief Description of the Drawings
Figure 1 shows discharge profiles of lithium-sulfur battery with n-Ci2H25SLi
added to the cathode for repeated charge/discharge cycles 3 to 63.
Figure 2 shows comparison of cycling performance of a cell prepared with
and without the anode being treated with 3,6-dioxaoctanc-1,8-dithiol di-
lithium salt
(LiS-C2F14-0-C2H4-0-C2H4-SLi).
Detailed Description of the Invention
An electroactive material that has been fabricated into a structure for use in
a
battery is referred to as an electrode. Of a pair of electrodes used in a
battery, which
serves as a chemical source of electrical energy, the electrode on the side
having a
higher electrochemical potential is referred to as the positive electrode, or
the cathode,
while the electrode on the side having a lower electrochemical potential is
referred to
as the negative electrode, or the anode. As used herein, the conventional
nomenclature for batteries is employed wherein the terms "cathode" or
"positive
electrode" and "anode" or "negative electrode" refer to the electrochemical
functions
of the electrodes during discharge of the cell to provide electrical energy.
During the
charging portion of the cycle, the actual electrochemical functions of an
electrode are
reversed versus that which occurs during discharge, but the designation of the
respective electrodes remains the same as for discharge.
Electrochemical cells are commonly combined in series, the aggregate of such
cells being referred to as a battery. Based on the operative chemistry of the
cells,
primary batteries are designed for a single discharge to provide power for an
external
device. Secondary batteries are rechargeable, using electrical energy from an
external
source, and thus offer extended use over multiple discharge and charge cycles.
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An electrochemically active material used in the cathode or positive electrode
is referred to hereinafter as a cathode active material. An electrochemically
active
material used in the anode or negative electrode is hereinafter referred to as
an anode
active material. Multi-component compositions possessing electrochemical
activity
and comprising an electrochemically active material and optional electrically
conductive additive and binder, as well as other optional additives, are
referred to
hereinafter as electrode compositions. A battery comprising a cathode with the
cathode active material in an oxidized state and an anode with the anode
active
material in a reduced state is referred to as being in a charged state.
Accordingly,
battery comprising a cathode with the cathode active material in a reduced
state, and
an anode with the anode active material in an oxidized state, is referred to
as being in
a discharged state.
Without wishing to be bound by theory, the following are certain possible
advantages or features of the present invention. The organosulfur species may
partition to the sulfur-rich catholyte phase. The chemical exchange reactions
between
dianionic sulfides or polysulfides (e.g., Li2S., x = 1, 2, 3...) and the
organopolysulfides, organothiolates or organopolythiolates (e.g., R-Sx-R' or R-
S.-Li,
R and R' = organic moieties, x = 0 or an integer of 1 or more), along with
sulfur
extrusion/reinsertion chemistries common to polysulfides and polythiolates,
favor
minimizing the amount of the dianionic polysulfides in the catholyte and favor
redeposition of sulfur and sulfur-containing species at the cathode. The net
removal
of the dianionic polysulfides would reduce the electrolyte viscosity and thus
minimize
the deleterious effects of high viscosity on electrolyte conductivity. The
organosulfur
species may also increase the dissolution, and thus scavenging, of insoluble
low-rank
lithium sulfide species (particularly Li2S and Li2S2) in both the catholyte
and anolyte
phases, thus minimizing loss of reactive lithium species upon repeated
charge/discharge cycles. The performance of the organosulfur species can be
"tuned"
by selection of the organic functionality. For example, short chain alkyl or
alkyl
groups with more polar functionality, would partition more to the anolyte
phase, while
the longer-chain or less-polar analogs would partition more to the catholyte
phase.
Adjusting the relative ratios of the long/nonpolar and short/polar chain
organic
species would provide a means of controlling the partition of sulfur-
containing
species to the cathode/catholyte. Moreover, since the presence of some amount
of
polysulfide or polythiolate in the anolyte is advantageous as a means of
controlling
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lithium dendrite growth on the anode during charging, selection of appropriate
organic moieties and their relative ratios would provide greater control of
dendrite
growth.
Organosulfur species useful in the present invention comprise at least one
organic moiety and at least one ¨S-Sn- linkage, wherein n is 0 or an integer
of at least
I. In one embodiment, the organosulfur species comprises two organic moieties
per
molecule (which may be the same as or different from each other) which are
linked by
a ¨S-Se- (polysulfide) linkage (wherein n is an integer of 1 or more). The ¨S-
Sn-
linkage may form part of a larger linking group such as a ¨Y1-C(Y2Y3)-S-Sn-
linkage
or a ¨Y1-C(=Y4)-S-Sn- linkage, wherein Y1 is 0 or S, Y2 and Y3 are
independently an
organic moiety or ¨S-S0-Z, where o is 1 or more and Z is an organic moiety or
a
species selected from Li, Na, K, Mg, quaternary ammonium, or quaternary
phosphonium, and Y4 is 0 or S. In another embodiment, the organosulfur species
contains a monovalent organic moiety and a species selected from Na, Li, K,
Mg,
quaternary ammonium and quaternary phosphonium which are linked by a ¨S-Sir
linkage (including, for example, a ¨Y1-C(Y2Y3)-S-Sn- linkage or ¨YI-C(=Y4)-S-
Sn-
linkage, where n =0 or an integer of I or more). In still another embodiment,
a ¨S-
Sn- linkage may appear on either side of an organic moiety. For example, the
organic
moiety can be a divalent, optionally substituted aromatic moiety, C(R3)2 (with
each R3
being independently H or an organic moiety such as a CI-C20 organic moiety),
carbonyl (C=0) or thiocarbonyl (C=S).
The organosulfur species may, for example, be selected from the group
consisting of organic polysulfides, organic thiolates, organic polythiolates,
including
those with sulfur-containing functional groups such as dithioacetal,
dithioketal, ...
trithio-orthocarbonate, aromatic polysulfide, polyether-polysulfide,
polysulfide-acid
salt, thiosulfonate [-S(0)2-S-], thiosulfinate [-S(0)-S-], thiocarboxylate [-
C(0)-S-],
dithiocarboxylate
[-RC(S)-S-], thiophosphate or thiophosphonate functionality, or mono-, di- or
trithiocarbonate functionality; organo-metal polysulfides containing these or
similar
functionalities; and mixtures thereof.
Suitable organic moieties include, for example, mono-, di- and polyvalent
organic moieties which may comprise branched, linear and/or cyclic hydrocarbyl
groups. As used herein, the term "organic moiety" includes a moiety which may,
in
addition to carbon and hydrogen, comprise one or more heteroatoms such as
oxygen,
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nitrogen, sulfur, halogen, phosphorus, selenium, silicon, a metal such as tin
and the
like. The heteroatom(s) may be present in the organic moiety in the form of a
functional group. Thus, hydrocarbyl as well as functionalized hydrocarbyl
groups are
considered within the context of the present invention to be organic moieties.
In one
embodiment, the organic moiety is a CI-Cm organic moiety. In another
embodiment,
the organic moiety contains two or more carbon atoms. The organic moiety thus
may
be a C2-C20 organic moiety.
The organosulfur species may be monomeric, oligomeric or polymeric in
character. For example, the ¨S-Sn- functionality may be pendant to the
backbone of
an oligomeric or polymeric species containing two or more repeating units of
monomer in its backbone. The ¨S-Se- functionality may be incorporated into the
backbone of such an oligomer or polymer, such that the oligomer or polymer
backbone contains a plurality of ¨S-Se- linkages.
The organosulfur species may, for instance, be an organic polysulfide or
mixture of organic polysulfides of formula RI-S-n-R2, wherein RI and R2
independently represent a CI-Cm organic moiety and n is an integer of 1 or
more. The
CI-Ca) organic moiety may be a monovalent branched, linear or cyclic
hydrocarbyl
group. RI and R2 may each independently be a C9-C14 hydrocarbyl group, with n
= 1
(providing a disulfide, such as tertiary-dodecyl disulfide). In another
embodiment, RI
and R2 are each independently a C9-C14 hydrocarbyl group, with n = 2-5
(providing a
polysulfide). Examples of such compounds include TPS-32 and TPS-20, sold by
Arkema. In another embodiment, RI and R2 are independently C7-CI hydrocarbyl
groups, with n = 2-5. TPS-37LS, sold by Arkema, is an example of a suitable
polysulfide of this type. Another type of suitable polysulfide would be a
polysulfide
or mixture of polysulfides wherein RI and R2 are both tert-butyl and n = 2-5.
Examples of such organosulfur compounds include TPS-44 and TPS-54, sold by
Arkema.
The organosulfur species could also be an organic polythiolate of formula RI-
S-Sn-M, wherein R1 is a CI-C20 organic moiety, M is lithium, sodium,
potassium,
magnesium, quaternary ammonium, or quaternary phosphonium and n is an integer
of
1 or more or an organic thiolate of formula R2-S-M, wherein R2 is a CI-C20
organic
moiety, M is lithium, sodium, potassium, magnesium, quaternary ammonium, or
quaternary phosphonium.
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In another embodiment, the organosulfur species may be a dithioacetal or
dithioketal such as those corresponding to formulas (I) and (II), or a trithio-
orthocarboxylate of formula (III):
R3 s¨So¨z
¨
R3`c/S
Z¨ So ¨S ¨C ¨S ¨Sp ¨Z R3¨C S¨S --Z
R3 /"R
S¨ SP R3 SSqZ
I II Ill
wherein each R3 is independently H or a Cl-C20 organic moiety, o, p and q are
each
independently an integer of 1 or more, and each Z is independently a C1-C20
organic
moiety, Li, Na, K, Mg, quaternary ammonium, or quaternary phosphonium.
Examples of such organosulfur species include 1,2,4,5-tetrathiane (formula I,
R3 = H,
o = p = 1), tetramethy1-1,2,4,5-tetrathiane (formula I, R3 = CiI3, o = p =1),
and oligo
or polymeric species thereof.
Another embodiment of the invention utilizes an organosulfur species which is
an aromatic polysulfide of formula (1V), a polyether-polysulfide of formula
(V), a
polysulfide-acid salt of formula (VI), or a polysulfide-acid salt of formula
(VII):
MO3S¨R5¨S¨So¨Z
0¨S¨So S ¨Sõ tk) VI
¨Z
R5 r R5
MO2C¨R7¨S¨S0--Z
IV V
VII
wherein R4 independently is tert-butyl or tert-amyl, R5 independently is OH,
OLi or
ONa. and r is 0 or more (e.g., 0-10) in formula (IV) with the aromatic rings
being
optionally substituted in one or more other positions with substituents other
than
hydrogen, R6 is a divalent organic moiety in formula (VI), R7 is a divalent
organic
moiety in formula (VII), each Z is independently a CI-C2o organic moiety, Li,
Na, K,
Mg, quaternary ammonium or quaternary phosphonium, each M is independently Li,
Na, K, Mg, quaternary ammonium, or quaternary phosphonium, and o and p are
each
independently an integer of 1 or more. Examples of such organosulfur species
include the aromatic polysulfides sold by Arkema under the brand name Vultac
(formula IV, R4 = tert-butyl or tert-amyl, R5 = OH); and polysulfide-acid
salts
corresponding to formulas VI and VII derived from mercapto-acids such as
mercaptoacetic acid, mercaptopropionic acid, mercaptoethanesulfonic acid,
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mercaptopropanesulfonic acid, or from olefin-containing acids such as
vinylsulfonic
acid or 2-acrylamido-2-methylpropanesulfonic acid.
In still another embodiment, the organosulfur species is an organo- or organo-
metal polysulflde containing trithiocarbonate functionality of formula (IX),
an
organo- or organo-metal polysulflde containing dithiocarbonate functionality
of
formula (X), or an organo- or organo-metal polysulflde containing
monothiocarbonate
functionality of formula (XI):
0 0
Sp ¨z
ix X XI
wherein Z is a Ci-C20 organic moiety, Na, Li, K, Mg, quaternary ammonium, or
quaternary phosphonitun, and o and p are independently an integer of 1 or
more.
The liquid or gel electrolyte solution may be additionally comprised of a
dimetal polythiolate species of formula M-S-S.-M, wherein each M is
independently
Li, Na, K, Mg, quaternary ammonium, or quaternary phosphonium and n is an
integer
of 1 or more. Such a species thus does not contain any organic moiety, unlike
the
above-described organosulfur species.
The intermediate separator element may function as a divider between
compartments in an electrochemical cell. One compartment may comprise an
electrolyte in contact with a cathode (the electrolyte in such compartment may
be
referred to as a catholyte). Another compartment may comprise an electrolyte
in
contact with an anode (the electrolyte in such compartment may be referred to
as an
anolyte). The anolyte and the catholyte may be the same as, or different from,
each
other. One or both of the anolyte and the catholyte may contain one or more
organosulfur species in accordance with the present invention. The
intermediate
separator element may be positioned between such compartments in a manner so
as to
permit ions from the anolyte to pass through the intermediate separator
element into
the catholyte and vice versa, depending upon whether the electrochemical cell
is
being operated in the charge or discharge mode.
In a further embodiment of the invention, the intermediate separator element
is
comprised of a porous polymer. The porous polymer may, for example, be
comprised
of polypropylene, polyethylene, or a fluorinated polymer. The porous polymer
may
be functionalized with an organosulfur species of the type described herein.
The
organosulfur species may be pendant to the backbone of the porous polymer, may
be
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present in crosslinks between the backbones of individual polymer chains
and/or may
be incorporated into the backbone of the porous backbone. Thus, the backbone
of the
porous polymer may contain one or more -S-Se- linkages and/or -S-S.- linkages
may
be pendant to the polymer backbone. Such -S-S.- linkages may also be present
in
crosslinks.
Suitable solvents to be used in electrochemical cells in accordance with the
invention include any of the basic (cation-complexing) aprotic polar solvents
known
or used for lithium-sulfur batteries generally such as sulfolane, dimethyl
sulfoxide,
dimethylacetamide, tetramethyl urea, N-methyl pyrrolidinone, tetraethyl
sulfamide;
ethers such as tetrahydrofuran, methyl-THF, 1,3-dioxolane, 1,2-dimethoxyethane
(glyme), diglyme, and tetraglyme, and mixtures thereof; carbonates such as
ethylene
carbonate, propylene carbonate, dimethylcarbonate, diethylcarbonate,
ethylmethylcarbonate, methylpropylcarbonate, ethylpropylcarbonate and the
like; as
well as esters such as methylacetate, ethyl acetate, propylacetate, and gamma-
butyrolactone. The electrolyte may comprise a single such solvent or a mixture
of
such solvents. Any of the polar aprotic polymers known in the battery art
could also
be employed. The electrolyte may comprise a polymeric material and may take
the
form of a gel. Suitable polymers for use in the electrolyte may include, for
example,
polyethylene oxide, a polyethersulfone, a polyvinylalcohol, or a polyimide.
The
electrolyte may be in the form of a gel, which may be a three-dimensional
network
comprised of a liquid and a binder component. The liquid may be a monomeric
solvent which is entrained within a polymer, such as a crosslinked polymer.
One or more conductive salts are present in the electrolyte in combination
with
the nonaqueous polar aprotic solvent and/or polymer. Conductive salts are well
known in the battery art and include, for example, lithium salts of
(CF3S02)21s1-,
CF3S03-, CH3S03-, C104-, PF6-, AsF6-, nitrate, halogen or the like. Sodium and
other alkali metal salts and mixtures thereof may also be used.
The anode active material may comprise an alkali metal such as lithium,
sodium, potassium and/or magnesium or another active material or composition.
Particularly preferred anode active materials include metallic lithium, alloys
of
lithium, metallic sodium, alloys of sodium, alkali metals or alloys thereof,
metal
powders, alloys of lithium and aluminum, magnesium, silicon, and/or tin,
alkali
metal-carbon and alkali metal-graphite intercalates, compounds capable of
reversibly
oxidizing and reducing with an alkali metal ion, and mixtures thereof. The
metal or
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metal alloy (e.g., metallic lithium) may be contained as one film within a
battery or as
several films, optionally separated by a ceramic material. Suitable ceramic
materials
include, for example, silica, alumina, or lithium-containing glassy materials
such as
lithium phosphates, lithium aluminates, lithium silicates, lithium phosphorus
oxynitrides, lithium tantalum oxide, lithium aluminosilicates, lithium
titanium oxides,
lithium silicosulfides, lithium germanosulfldes, lithium aluminosulfides,
lithium
borosulfides, lithium phosphosulfldes and mixtures thereof.
The anode may be in any suitable form, such as, for example, a foil, composite
or other type of current collector.
In one embodiment of the invention, the anode is treated with at least one
organosulfur species. Such treatment may be carried out by contacting a
surface of
the anode with the at least one organosulfur species. The organosulfur species
may,
for example, be in the form of a solution during such contacting step. Any
suitable
solvent or combination of solvents for the organosulfur species may be
utilized to
form such a solution. For example, the solvent(s) may be any of the aprotic
polar
solvents previously described. In one embodiment, the anode is treated with
the
organosulfur species prior to assembly of an electrochemical cell, such as by
spraying
a solution of the organosulfur species onto the anode or dipping the anode
into a
solution of the organosulfur species. In another embodiment, the organosulfur
species
is incorporated as a component of the electrolyte to be employed in the
electrochemical cell, wherein the electrolyte containing the organosulfur
species
comes into contact with the anode upon assembly of the electrochemical cell.
In another embodiment, the anode comprises at least one organosulfur species
in addition to at least one reactive metal selected from the group consisting
of lithium,
sodium, potassium and magnesium. For example, at least one organosulfur
species
may be deposited on a surface of the anode.
The cathode comprises elemental sulfur, elemental selenium or a mixture of
elemental chalcogens. In one embodiment, the cathode is additionally comprised
of
one or more organosulfur species in accordance with those previously described
in
detail herein. The cathode may additionally and/or alternatively be comprised
of a
binder and/or an electrically conductive additive. Suitable binders include
polymers
such as, for example, polyvinyl alcohol, polyacrylonitrile, polyvinylidene
fluoride
(PVDF), polyvinyl fluoride, polytetrafluoroethylene (PTFE), copolymers from
tetrafluoroethylene and hexafluoropropylene, copolymers from vinylidene
fluoride
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and hexafluoropropylene, copolymers from vinylidene fluoride and
tetrafluoroethylene, ethylene-propylene-diene monomer rubber (EPDM), and
polyvinyl chloride (PVC). The electrically conductive additive may be, for
example,
a carbon in electrically conductive form such as graphite, giaphene, carbon
fibers,
carbon nanotubes, carbon black, or soot (e.g., lamp or furnace soot). The
cathode
may be present in a battery or electrochemical cell in combination with a
current
collector, such as any of the current collectors known in the battery or
electrochemical
cell art. For example, the cathode may be coated on the surface of a metallic
current
collector.
Aspects of the invention Include:
1. A battery, comprising:
a) an anode comprising an anode active material comprising sodium, lithium
or an alloy or composite of at least one of sodium or lithium with at least
one other
metal for providing ions;
b) a cathode comprising a cathode active material comprising elemental sulfur,
elemental selenium or a mixture of elemental chalcogens; and
c)an intermediate separator element positioned between the anode and cathode
acting to separate liquid or gel electrolyte solutions in contact with the
anode and
cathode, through which metal ions and their counterions move between the anode
and
cathode during charge and discharge cycles of the battery;
wherein the liquid or gel electrolyte solutions comprise a nonaqueous polar
aprotic
solvent or polymer and a conductive salt and at least one of conditions (i),
(ii), (iii) or
(iv) is met:
(i) at least one of the liquid or gel electrolyte solutions additionally
comprise at least
one organosulfur species;
(ii) the cathode is additionally comprised of at least one organosulfur
species;
(iii) the intermediate separator element comprises a functionalized porous
polymer
containing at least one organosulfur species;
(iv) the anode is additionally comprised of or has been treated with at least
one
organosulfur species;
wherein the organosulfur species comprises at least one organic moiety and at
least
one ¨S-Se- linkage, n being 0 or an integer of 1 or more.
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2. The battery of aspect I, wherein the organosulfur species is selected from
the
group consisting of organic polysulfides, organic thiolates and organic
polythiolates
and mixtures thereof
3. The battery of any one of aspects 1 and 2, wherein the organosulfur species
contains one or more sulfur-containing functional groups selected from the
group
consisting of dithioacetal, dithioketal, trithio-orthocarbonate, thiosulfonate
[-S(0)2-S-
], thiosulfinate [-S(0)-S-], thiocarboxylate [-C(0)-S-], dithiocarboxylate [-
C(S)-S-],
thiophosphate, thiophosphonate, monothiocarbonate, dithiocarbonate,and
trithiocarbonate.
4. The battery of any one of aspects 1-3, wherein the organosulfur species is
selected
from the group consisting of aromatic polysulfides, polyether-polysulfides,
polysulfide-acid salts and mixtures thereof.
5. The battery of any one of aspects 1-5, wherein the organosulfur species is
an
organic polysulfide of formula R1-S-Sn-R2, wherein RI and R2 independently
represent a Ci-C20 organic moiety that may be linear, branched, or cyclic
aliphatic or
aromatic and that may optionally comprise one or more functional groups
containing
N, 0, P, S, Se, Si, Sn, halogen and/or metal, and n is an integer of 1 or
more.
6. The battery of any one of aspects 1-5, wherein the organosulfur species is
an
organic thiolate of formula R1-S-M or organic polythiolate of formula R1-S-Sn-
M,
wherein RI is a CI-C20 organic moiety that may be linear, branched, or cyclic
aliphatic
or aromatic and that may optionally comprise one or more functional groups
containing N, 0, P, S, Se, Si, Sn, halogen and/or metal, M is lithium, sodium,
potassium, magnesium, quaternary ammonium, or quaternary phosphonium, and n is
an integer of 1 or more.
7. The battery of any one of aspects 1-6, wherein the organosulfur species is
a
dithioacetal or dithioketal of formulas (I) or (II), or a trithio-
orthocarboxylate of
formula (III):
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/
S50 R3
3
R
R3-C--S---S
R3
S-SP R3 S S ¨Z
I II HI
wherein each R3 is independently H or a CI-C20 organic moiety that may be
linear,
branched, or cyclic aliphatic or aromatic and that may optionally comprise one
or
more functional groups containing N, 0, P. S, Se, Si, Sn, halogen and/or
metal, o, p
and q are each independently an integer of 1 or more, and each Z is
independently: a
CI-C20 organic moiety that may be linear, branched, or cyclic aliphatic or
aromatic
and that may optionally comprise one or more functional groups containing N,
0, P,
S, Se, Si, Sn, halogen and/or metal; Li; Na; K; Mg; quaternary ammonium; or
quaternary phosphonium.
8. The battery of any one of aspects 1-7, wherein the organosulfur species is
an
aromatic polysulfide of formula (IV), a polyether-polysulfide of formula (V),
a
polysulfide-acid salt of formula (VI), or a polysulfide-acid salt of formula
(VII):
R4
mo3S-R6-S-S0-2
S-s
R5 Rs / R5
MO2C-R7-S-S0-Z
iv V VII
wherein R4 independently is tert-butyl or tert-amyl, R5 independently is OH,
OLi or
ONa, and r is 0 or more in formula (IV) with the aromatic rings being
optionally
substituted in one or more positions with substituents other than hydrogen, R6
is a
divalent organic moiety in formula (VI), R5 is a divalent organic moiety in
formula
(VII), each Z is independently a Ci-C20 organic moiety, Li, Na or quaternary
ammonium, each M is independently Li, Na, K, Mg, quaternary ammonium, or
quaternary phosphonium, and o and p are each independently an integer of 1 or
more.
9. The battery of any one of aspects 1-8, wherein the organosulfiir species is
an
organo- or organo-metal polysulfide containing trithiocarbonate functionality
of
formula (IX), an organo- or organo-metal polysulfide containing
dithiocarbonate
functionality of formula (X), or an organo- or organo-metal polysulfide
containing
monothiocarbonate functionality of formula (X1):
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0 0
11 11 11
Z-So-S-c-S-Sp-Z Z-So-S-C-S-Sp-Z Z-0-C¨S¨S
IX X XI
wherein 2 is a C1-C20 organic moiety, Na, Li, quaternary ammonium or
quaternary
phosphonium, and o and p are each independently an integer of 1 or more.
10. The battery of any one of aspects 1-9, wherein the liquid or gel
electrolyte
solution is additionally comprised of a dimetal polythiolate species of
formula M-S-
SvM, wherein each M is independently Li, Na, K, Mg, quaternary ammonium, or
quaternary phosphonium, and n is an integer of 1 or more.
11. The battery of any one of aspects 1-10, wherein the cathode is
additionally
comprised of at least one electrically conductive additive and/or at least one
binder.
12. The battery of any one of aspects 1-11, wherein the organosulfur species
is
pendant to the backbone of the fimctionalized porous polymer.
13. The battery of any one of aspects 1-12, wherein the organosulfur species
is
crosslinked into or forms part of the backbone of the functionalized porous
polymer.
14. The battery of any one of aspect 1-13, wherein the organic moiety contains
at
least two carbon atoms.
15. The battery of any one of aspects 1-14, wherein the intermediate porous
separator separates the battery to provide an anolyte section associated with
the anode
and a catholyte section associated with the cathode and wherein the
organosulfur
species is present in at least one of the anolyte section or the catholyte
section.
16. The battery of any one of aspects 1-15, wherein the non-aqueous polar
aprotic
solvent or polymer contains one or more functional groups selected from ether,
carbonyl, ester, carbonate, amino, am ido, sulfidyl [-S-], sulfinyl [-S(0)-],
or sulfonyl
[-SO2-].
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17. The battery of any one of aspects 1-16, wherein the conductive salt
corresponds
to formula MX wherein M is Li, Na or quaternary ammonium and X is (CF3S02)2N,
CF3S03, CH3S03, C104, PF6, NO3, AsF6 or halogen.
18. The battery of any one of aspects 1-17, wherein the organic moiety is
oligomeric
or polymeric and the organosulfur species comprises at least one ¨S-S- linkage
that is
pendant to the backbone of the oligomeric or polymeric organic moiety.
19. The battery of any one of aspects 1-18, wherein the organic moiety is
oligomeric
or polymeric and the organosulfur species comprises at least one ¨S-S- linkage
that in
incorporated into the backbone of the oligomeric or polymeric organic moiety.
20. An electrolyte, comprising at least one nonaqueous polar aprotic solvent
or
polymer, at least one conductive salt, and at least one organosulfur species
comprised
of at least one organic moiety and at least one ¨S-Se- linkage wherein n is 0
or an
integer of 1 or more.
21. A cathode comprising a) elemental sulfur, elemental selenium or a mixture
of
elemental chalcogens, b) at least one electrically conductive additive, c) and
at least
one organosulfur species comprising at least one organic moiety and at least
one ¨S-
Sn- linkage, n being 0 or an integer of 1 or more.
22. The cathode of aspect 21, in combination with a current collector.
23. The cathode of any one of aspects 21 and 22, wherein the at least one
electrically
conductive additive includes at least one of graphite, carbon nanotubes,
carbon
nanofibers, graphene, carbon black or soot.
24. The cathode of any one of aspects 21-23, additionally comprising at least
one
binder.
25. An anode comprising an anode active material comprising sodium, lithium,
potassium or magnesium or an alloy or composite of at least one of sodium,
lithium,
potassium or magnesium with at least one other metal for providing ions,
wherein the
anode additionally comprises or has been treated with at least one
organosulfur
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species comprising at least one organic moiety and at least one ¨S-Se-
linkage, n
being 0 or an integer of 1 or more.
Within this specification embodiments have been described in a way which
enables a clear and concise specification to be written, but it is intended
and will be
appreciated that embodiments may be variously combined or separated without
departing from the invention. For example, it will be appreciated that all
preferred
features described herein are applicable to all aspects of the invention
described
herein.
In some embodiments, the invention herein can be construed as excluding any
element or process step that does not materially affect the basic and novel
characteristics of the composition or process. Additionally, in some
embodiments, the
invention can be construed as excluding any element or process step not
specified
herein.
EXAMPLES
Cathode Fabrication. Battery Preparation, and Battery Testing
Example 1
A positive electrode comprising 70 wt% sublimed elemental sulfur powder. 20
wt%
polyethylene oxide (PEO, MW 4x106), 10 wt% carbon black (Super Pe Conductive,
Alfa Aesar) was produced by the following procedure:
The mixture of these components in N-methyl-2-pyrrolidone (NMI') was
mechanically ground in a planetary milling machine. Acetonitrile was added to
dilute
the mixture. The resulting suspension was applied onto aluminum foil (76 urn
thickness) with an automatic film coater (Mathis). The coating was dried at 50
C in a
vacuum oven for 18 hrs. The resulting coating contained 3.10 mg/cm2 cathode
mixture.
Example 2
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A positive cathode containing lithium n-dodecyl mercaptide (10 wt% of sulfur)
was
prepared following the procedure described in Example 1. The resulting coating
contained 3.4 mg sulfur/cm2
Example 3
The positive cathode from Example 2 was used in a PTFE Swaglok cell with two
stainless steel rods or coin cell assembly made of stainless steel (CR2032).
The
battery cell was assembled in an argon filled glove box (MBraun) as follows:
the
cathode electrode was placed on the bottom can followed by the separator. Then
electrolyte was added to the separator. A lithium electrode was placed onto of
the
separator. A spacer and a spring were placed on top of the lithium electrode.
The
battery core was sealed with the stainless steel rods or with a crimping
machine.
Example 4
Following the procedure described in Example 3, a battery cell consisting of
cathode
from Example 2 (7/16" diameter), 20 pi, of 0.5 M LiTFSI solution in
tetraethylene
glycol dimethyl ether (TEGDME):1,3-dioxolane (DOL)=1:1, separator, and lithium
electrode (thickness 0.38 mm, diameter 7/16") was tested for charge-discharge
cycling at a current of 0.1 mA. The testing was carried out using Gamry
potentiometer (Gamry Instruments) to cut-off voltage of 1.5 V and 3.2 V at
room
temperature. The discharge cycle profile is illustrated in Figure 1.
Syntheses of lithium alkylmercaptides
Example 5 - Synthesis of lithium n-dodecyl mercaptide with hexyl lithium
To n-dodecyl mercaptan (9.98 g, 1 eq.) in hexanes (100 mL) at -30 C was added
n-hexyllithium (33 wt% in hexane, 1.1 eq.) dropwise to maintain mixture
temperature
below -20 C. The solvent was removed under reduced pressure to yield a white
solid
at quantitative yield.
Example 6 - Synthesis of lithium n-dodecyl mercaptide with lithium hydroxide
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A mixture of n-dodecyl mercaptan (2.0 g, 1 eq.) and lithium hydroxide
monohydrate
(0.41 g, 1 eq.) in acetonitrile (8 mL) was heated to 75 C and stirred at 75
C for 16
hrs. After cooling to room temperature, the reaction mixture was filtered. The
filter
cake was rinsed with acetonitrile and dried at 50 C in a vacuum oven over
night. The
lithium n-dodecylmercaptide was obtained as a white solid in 93.5% yield (1.93
g)
Example 7 - Synthesis of lithium n-dodecyl mercaptide with hexyl lithium
0 SU
Following the procedure described in Example 6, 3,6-dioxaoctane-1,8-dithiol di-
lithium salt was synthesized from the di-mercaptan as a white solid in
quantitative
yield.
Syntheses of lithium alkyl polythiolates
Example 8 - Synthesis of lithium n-dodecylpolythiolate with lithium hydroxide
To a nitrogen degassed solution of n-dodecyl mercaptan (2.00 g, 1 eq.) in 1,3-
dioxolane (25 mL) was added lithium hydroxide monohydrate (0.41 g, 1 eq.) and
sulfur (1.27 g, 4 eq.). The mixture was stirred under nitrogen at room
temperature for
min. Lithium n-dodecyl polythiolate in 1,3-dioxolane was obtained as a dark
red
solution. Complete conversion of mercaptan to lithium n-dodecyl polythiolate
was
25 confirmed by 13C-NMR and LCMS.
Example 9 - Synthesis of lithium 3,6-dioxaoctane-1,8-polythiolate with lithium
hydroxide and sulfur
Following the procedure described in Example 8, dark red solution of lithium
3,6-
dioxaoctane-1,8-polythiolate in 1,3-dioxolane from reaction of 3,6-dioxaoctane-
1,8-
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dithiol (0.72 g, 1 eq.), lithium hydroxide monohydrate (0.33 g, 2 eq.), and
sulfur (1.02
g, 8 eq.) in 1,3-dioxolane (10 mL).
Example 10 - Synthesis of lithium n-dodecylpolythiolate from the lithium alkyl
mercaptide
To a nitrogen degassed slurry of lithium n-dodecyl mercaptide (0.21 g, 1 eq.)
in
1,3-dioxolane (5 mL) was added sulfur (0.13 g, 4 eq.). The mixture was stirred
under
nitrogen at room temperature for 16 hrs. Insoluble solids were removed by
filtration.
The dark red filtrate contained 63% of lithium n-dodecyl polythiolates and 37%
of a
mixture of bis(n-dodecyl)polysulfides as determined by LCMS.
Example 11 - Synthesis of lithium n-dodecylpolythiolate with lithium metal and
sulfur
To a nitrogen degassed solution of n-dodecyl mercaptan (2.23 g, 1 eq.) in 1,3-
dioxolane (25 mL) was added sulfur (1.41 g, 4 eq.), and lithium (76.5 mg). The
mixture was heated to 60 C and stirred under nitrogen at 60 C for 1 hr.
Lithium n-
dodecyl polythiolate in 1,3-dioxolane was obtained as a dark red solution.
Complete
conversion of n-dodecyl mercaptan was confirmed by "C-NMR.
Example 12¨ Synthesis of lithium 3,6-dioxaoctane-1,8-polythiolate with lithium
metal and sulfur
Following the procedure in Example 11, a dark red solution of lithium 3,6-
dioxaoctane-1,8-polythiolate in 1,3-dioxolane was obtained by reaction of 3,6-
dioxaoctane-1,8-dithiol (1.97 g, 1 eq.), lithium metal (0.15 g, 2 eq.), and
sulfur (2.77
g, 8 eq.) in 1,3-dioxolane (11 mL). Complete conversion of starting di-
mercaptan was
confirmed by 13C-NMR
Example 13 ¨ Dissolution of Li2S by added lithium n-dodecylpolythiolate
To determine the solubility of lithium sulfide in electrolyte with lithium
n-dodecylpolythiolate, a saturated solution of lithium sulfide was prepared as
follows:
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A 0.4 M solution of lithium n-dodecylpolythiolate in 1,3-dioxolane was
prepared
following procedures described in Example 10. The solution was then diluted to
0.2
M with tetraethylene glycol dimethyether, then added to 1M LiTFSI solution in
1:1
tetraethylene glycol dimethylether:1,3-dioxolane at 1:1 = v/v. To the
resulting
solution, lithium sulfide was added until a saturated mixture was obtained.
The
mixture was then filtered and the filtrate was analyzed for dissolved lithium
by ICP-
MS (Agilent 7700x ICP-MS). The solubility of lithium sulfide was calculated
based
on the lithium level. In 0.5 M LiTFSI with 0.1 M lithium n-dodecylpolythiolate
in 1:1
tetraethylene glycol dimethylether:1,3-dioxolane, solubility of lithium
sulfide was
.. determined to be 0.33 wt%. In contrast, without lithium n-
dodecylpolythiolate, the
solubility of lithium sulfide in 0.5 M LiTFSI was only 0.13 wt%. This clearly
demonstrated the improved solubility of Li2S in the electrolyte matrix of the
battery
when the organosulfurs of this invention are present.
Example 14¨ Preparation of Battery containing Organosul fur Species-Treated
Anode
This example demonstrates the preparation of a battery cell that has an anode
that has
been exposed to an electrolyte containing an organosulfitr species in
accordance with
one aspect of the invention. Elemental sulfur was combined with conductive
carbon
and polyethylene (as a binder) in a mass ratio (sulfur:carbon:polyethylene) of
75:20:5
and ball milled into a slurry with chloroform. The slurry was then blade-cast
onto
carbon-coated aluminum foil and air-dried, resulting in a sulfur loading of
approximately 0.5 mg/cm2. The resulting cathode was then assembled into CR2032
coin cells with a polypropylene separator and a lithium foil anode in an argon-
tilled
glove box. The electrolytes used each contained 0.38 M lithium
bis(trifluoromethane)sulfonamide and 0.38 M lithium nitrate in a 1:1 v/v
mixture of
1,3-dioxolane and 1,2-dimethoxyethane. One electrolyte (in accordance with the
present invention) additionally contained 100 mM 3,6-dioxaoctane-1,8-dithiol
di-
lithium salt (LiS-C2F14-0-C2H4-0-C2H4-SLi) (thereby bringing the lithium foil
anode
.. into contact with 3,6-dioxaoctane-1,8-dithiol di-lithium salt), while the
other
electrolyte (control) did not contain any organosulfur species. Battery
cycling was
done on a battery test from 1.7 to 2.6 V. 40 at C/2 with respect to active
sulfur. The
results observed are shown in Figure 2.
23
