Protected bis(hydroxyorganyl) polysulfides as modifiers of Li/S battery electrolyte

Article abstract of DOI:10.1016/j.electacta.2010.11.064

The protected bis(hydroxyorganyl) polysulfides synthesized have been tested as modifiers of electrolyte of lithium-sulfur rechargeable batteries. The best result (35% increase of the battery capacity at the 50th cycle) was attained using 5 wt.% of 2,2,12,

Full text of DOI:10.1016/j.electacta.2010.11.064

Electrochimica Acta 56 (2011) 2458–2463
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Protected bis(hydroxyorganyl) polysulfides as modifiers of Li/S
battery electrolyte
Boris A. Trofimova,∗, Marina V. Markovaa, Lyudmila V. Morozovaa, Galina F. Prozorovaa,
Svetlana A. Korzhovaa, Myung D. Chob, Vadim V. Annenkova, Al’bina I. Mikhalevaa
a A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 Favorsky St., Irkutsk 664033, Russian Federation
b Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The protected bis(hydroxyorganyl) polysulfides synthesized have been tested as modifiers of electrolyte
of lithium-sulfur rechargeable batteries. The best result (35% increase of the battery capacity at the 50th
cycle) was attained using 5 wt.% of 2,2,12,12-tetramethyl-4,10-diphenyl-3,11-dioxa-6,7,8-trithia-2,12-
disilatridecane. Bis(hydroxyorganyl) polysulfides protected at the hydroxyl group have been synthesized
for the first time by the reaction of oxiranes with sodium polysulfide (ethanol, NaHCO3, 12 h, 20–25 ◦C)
in yield 21–87%. For the hydroxyl protection in the hydroxy polysulfides, the acetal, tri(methyl)silyloxy
or tri(ethoxy)silyl protecting groups were employed.
Received 16 June 2010
Received in revised form
13 November 2010
Accepted 20 November 2010
Available online 30 November 2010
Keywords:
© 2010 Elsevier Ltd. All rights reserved.
Lithium/sulfur batteries
Bis(hydroxyorganyl) polysulfides
Acetal
Tri(methyl)silyloxy
Tri(ethoxy)silyloxy protecting groups
Electrolyte
Modifiers
1. Introduction
polysulfides results in self-discharge of the battery, for example:
S82− + 2Li → S72− + Li2S
Li-metal batteries are considered to be very attractive due to
their high energy density [1]. Elemental sulfur seems to be the best
cathode material for these batteries because of its high theoretical
capacity (1672 mAh g−1) which allows one to have a specific energy
of 2600 Wh kg−1, assuming the complete reaction of lithium with
sulfur to Li2S [2–4].
The development of Li/S batteries is now carried out by a number
of companies and scientific centers and a commercially accept-
able design of these power sources is under way [5–9]. The unique
feature of Li/S battery is “liquescent cathode”: during the first
discharge cycle, almost the whole sulfur turns to higher lithium
polysulfides.
Finally, these reactions result in formation of insoluble lithium
sulfides and disulfides (Li2S and Li2S2) which just reluctantly or
not at all participate in the redox processes thereby decreasing the
content of active sulfur in the battery and deteriorating the surface
of lithium anode. The accumulation of insoluble sulfides over the
electrodes is commonly considered as a reason of poor cycle-life
of Li/S batteries [2–4,10]. According to the patent [11], lithium sul-
fide and disulfide can produce a passivating layer during deposition
onto the surface of a metal lithium electrode. This layer slows down
or completely prevents further interaction of metal lithium with
components of the electrolyte system. Generally it is well known
that diorganyl polysulfides react with alkaline metal sulfides to give
soluble longer-chain alkaline metal polysulfides [12–14].
S8 + 2Li0 → Li+−S8−Li+
This work deals with the synthesis of protected bis
(hydroxyorganyl) polysulfides, which can react with lithium sul-
fide and disulfide with the formation of soluble and more mobile
lithium compounds (organolithium polysulfides or mercaptides),
thus improving the Li/S battery performance.
The polysulfides are soluble in electrolyte and can diffuse to
the anode area. The reaction between lithium anode and higher
These species solubilize lithium sulfide and disulfide and move
to the cathode to participate in electrochemical reactions with
regeneration of soluble polysulfide molecules. So, these polysul-
∗
Corresponding author. Tel.: +7 3952 511431; fax: +7 3952 419346.
E-mail address: boris trofimov@irioch.irk.ru (B.A. Trofimov).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.11.064

B.A. Trofimov et al. / Electrochimica Acta 56 (2011) 2458–2463
2459
fides might act as a kind of catalytic carriers for insoluble Li2S and
2.2. Materials
Li2S2. Compounds described for the first time in this paper belong to
the class of organic polysulfides R–Sn–R. Their efficiency as lithium
sulfide and disulfide incorporating agents follows from the known
property of inorganic sulfides to be inserted into the S–S bonds [15],
therefore the following reactions are expected:
All solvents were dried by standard methods and distilled before
use. Chemically pure sodium sulfide Na2S·9H2O, NaHCO3, MgSO4,
K2CO3 and elemental sulfur were used.
2-Phenyloxirane
(1),
N-butoxyethene,
2-[(allyloxy)
methyl]oxirane (2) (“Aldrich”) were distilled before use.
The purity of 2-{[2-(vinyloxy)ethoxy]methyl}oxirane (3) was
99.99% (GLC control). Physical constants of 2-{[2-(vinyloxy)ethoxy]
methyl}oxirane corresponded to the literature (bp 77 ◦C/6 Torr,
Li2S + R2Sn → RSxLi + RSyLi
where n ≥ 2, x + y = n + 1.
20
20
nD 1.4480, d4 1.0333 [17].
Generally, lithium organylsulfides (mercaptides) thus formed
should be soluble in the battery electrolyte and their oxidation at
cathode recovers organic polysulfides:
The sodium polysulfide was synthesized from Na2S·9H2O and ele-
mental sulfur [18]: to a solution of Na2S·9H2O (6.0 g, 25.0 mmol) in
5 ml of water and 1 ml of ethanol, 3.2 g (100 mmol) of elemental sul-
fur was added at 50–60 ◦C over 20 min by portions (0.1–0.2 g). The
mixture was heated at 60 ◦C for 1 h and cooled to room temperature.
1-(2-oxiranylmethyl)-1H-pyrrole (4) was synthesized in a yield of
39% from 1H-pyrrole and 2-(chloromethyl)-oxirane by the proto-
col developed for 1-oxiranylmethyl-4,5,6,7-tetrahydroindole [19].
The process was realized through the reaction of the K salt of
1H-pyrrole, prepared from KOH and 1H-pyrrole in toluene with
azeotropic removal of water followed by the interaction of the salt
obtained with 2-(chloromethyl)-oxirane (60 ◦C, 3 h).
−
RSxLi + RSyLi−−2→e R Sx+y + 2Li+
2
In the patent [16], this approach was partially exemplified
using some hydroxyorganyl polysulfides. However, these polysul-
fides should irreversibly consume Li-anode due to the reaction
between Li-metal and hydroxy group with undesirable evolution
of hydrogen.
0
1-(2-oxiranylmethyl)-1H-indole (5) was synthesized in a yield
of 36% from 1H-indole and 2-(chloromethyl)-oxirane (45 ◦C,
3 h) by the protocol developed for 1-oxiranylmethyl-4,5,6,7-
tetrahydroindole [19].
2 R-CH-CH S Li + 2 Li
2 R-CH-CH S Li + 2 H
2 x
2 x
2
OLi
OH
Mixed 1,3-dioxolan-4-ylmethyl 2-oxiranylmethyl ether and 1,3-
dioxan-5-yl 2-oxiranylmethyl ether (6) (3:1) was synthesized in a
yield of 21% from the mixture of 1,3-dioxolan-4-ylmethanol and
1,3-dioxan-5-ol (35:65%), powdered NaOH and 2-(chloromethyl)
oxirane for 3 h at room temperature.
To avoid this drawback, here we have synthesized and
tested as electrolyte modifiers of Li/S battery a series of hith-
erto unknown protected hydroxyorganyl polysulfides, in which
hydroxy groups are converted to the acetal, tri(methyl)silyloxy or
tri(ethoxy)silyloxy functions.
2.3. Synthesis of the additives
2. Experimental
The typical procedures of the syntheses were as follows.
2.1. Measurements
2.3.1. Synthesis of hydroxyorganyl polysulfides
IR spectra were recorded on a Bruker IFS-25 spectrometer. NMR
spectra were run on a Bruker DPX 400 instrument [400.13 (1H)
MHz] in CDCl3 using HMDS as an internal standard.
2-[3-(2-hydroxy-2-phenylethyl)trisulfanyl]-1-phenyl-1-ethanol
(7) was synthesized according to Scheme 1 (see Section 3).
To a mixture of 2-phenyloxirane 1 (10.0 g, 83.2 mmol), ethanol
(5 ml) and NaHCO3 (5.0 g), a solution of sodium polysulfide (see
above) was added portion-wise (∼0.2 ml) under stirring over 1.5 h
at 20–25 ◦C. The resultant mixture was stirred for additional 2 h,
allowed to stay for 12 h and filtered off. The filtrate was diluted
with water (10 ml) and extracted with diethyl ether (5 × 10 ml). The
ether extract was dried over MgSO4 (4.0 g, 12 h) and distilled off.
The residue was distilled under vacuum (2 Torr, 70–100 ◦C), and
2.8 g of 2-phenyloxirane 1 was recovered. The residue is hydrox-
yorganyl polysulfide 7, a yellow resin-like substance (yield 5.0 g,
49% based on the reacted oxirane), soluble in diethyl ether, ethanol,
benzene, DMSO, etc. Molecular mass (cryoscopy in dioxane): 338.7.
Calcd: 338.5.
Two electrode electrochemical cells (model of button cell) were
used for electrochemical testing of the synthesized compounds. A
lithium anode and an aluminum cathode coated with carbon and
a composition based on elemental sulfur, activated carbon, and
polyethylene oxide in a ratio of 65:30:5 (wt.%) were employed. The
sulfur density on the cathode was 1.11 mg cm−2. The anode was
an Li metal foil of 0.2 mm thick. A 2 M solution of (CF3SO2)2NLi
in a 1:1 mixture of 1,2-dimethoxyethane and 1,3-dioxolane was
served as standard electrolyte. The Li/S cell cycling was performed
on a Maccor battery tester at a discharge–charge current density
of 0.25 mA cm−2 in a potential range from 1.25 V to 2.80 V at an
ambient temperature.
R
NaHCO3 (H2O)
R
R
Na2Sm
Sn
+
O
OH
N
OH
7-12
1-6
m = 2-5; n = 2-3
R = Ph (1, 7); CH2=CH-CH2-O- (2, 8); CH2=CHOCH2CH2O- (3, 9);
;
(4, 10)
N
(5, 11);
O
and
(6, 12).
O
O
O
O
O
Scheme 1. Synthesis of the starting hydroxyorganyl polysulfides.

2460
B.A. Trofimov et al. / Electrochimica Acta 56 (2011) 2458–2463
R
R
O
CF3CO2H
R
R
Sn
+
Sn
OBu-n
Me
O
O
Me
OH
OH
OBu-n
n-Bu
7
n = 2-3
13
R = Ph
Scheme 2. Synthesis of the polysulfide 13.
R
R
R
R
+
(Me3Si)2NH
Sn
Sn
- NH3
Me3Si
O
N
O
OH
OH
SiMe3
n = 2-3
7-12
14-19
R = Ph (7, 14); CH2=CH-CH2-O- (8, 15); CH2=CHOCH2CH2O- (9, 16);
;
(10, 17)
N
(11, 18);
O
and
(12, 19).
O
O
O
O
O
Scheme 3. Synthesis of the polysulfide 14–19.
1H NMR (acetone-D6), ı, ppm: 0.08s (18H, CH3), 2.57–4.18m
(4H, CH2S); 4.20–5.09m (2H, CH–CH2S), 7.36 (7.20–7.40)m (10H,
Ph); IR (neat, cm−1): 3085, 3061, 3029 (␯, CH, Ph); 2955, 2896,
2864 (␯, CH3, CH2, CH); 1946, 1873, 1803, 1723 (overtones, Ph);
1601, 1584 (␯, C C, Ph); 1493, 1453, 1204, (␯, C–C; ı, C–C–S; ı,
CH2); 1250 (ı, Si–CH3); 1025–1170 (␯, C–O–C, Si–O–C); 918, 875,
616 (␯, C–S); 841 (␯, Si–C); 749, 697 (ı, CH, Ph); 525 (␯, S–S);
elemental analysis calcd (%) for C22H34O2S3Si2: C, 54.72; H, 7.10; S,
19.92; Si, 11.63; found: C, 54.46; H, 7.22; S, 20.01; Si, 11.45.
Allyl 3-(3-{3-(allyloxy)-2-[(trimethylsilyl)oxy]propyl}trisulfanyl)-
2[(trimethylsilyl)oxy]propyl ether 15 was synthesized from 2-
[(allyloxy)methyl]oxirane 2 and hexamethyldisilazane according
to Schemes 1 and 3 in 81% yield as light-yellow mobile liquid, sol-
uble in diethyl ether, acetone, dioxane, 1,2-dimethoxyethane and
insoluble in water.
Hydroxyorganyl polysulfides 8–12 were prepared by analogical
methodic.
2.3.2. The reaction of hydroxyorganyl polysulfide with
N-butoxyethene
2-{3-[2-(1-Butoxyethoxy)-2-phenylethyl]trisulfanyl}-1-
phenylethyl 1-butoxyethyl ether 13 was prepared according to
Scheme 2 (see Section 3).
The hydroxyorganyl polysulfide
7 (3.5 g, 10.3 mmol) was
dissolved in 1,2-dimethoxyethane (2 ml), then N-butoxyethene
(2.00 g, 20.0 mmol) and trifluoroacetic acid (0.04 ml) were added.
The solution was stirred for 12 h at 20 ◦C. Then, K2CO3 (0.2 g) was
added to the solution, the resultant mixture was allowed to stay for
1 h at room temperature and filtered off. Excess of N-butoxyethene
and the solvent (1,2-dimethoxyethane) were removed by vacuum
distillation to give 5.57 g (100% yield) of polysulfide 13, a yellow
viscous liquid, soluble in diethyl ether, 1,2-dimethoxyethane and
insoluble in water.
2,2-Dimethyl-10-[(trimethylsilyl)oxy]-4-{[2-(vinyloxy)ethoxy]
methyl}-3,12,15-trioxa-6,7,8-trithia-2-sila-16-heptadecene 16 was
synthesized from 2-{[2-(vinyloxy)ethoxy]methyl}oxirane 3 and
hexamethyldisilazane according to Schemes 1 and 3, in 85% yield as
light-yellow liquid, soluble in diethyl ether, 1,2-dimethoxyethane
and insoluble in water.
2.3.3. The reactions of hydroxyorganyl polysulfides with
hexamethyldisilazane
1H NMR (CDCl3), ı, ppm: 0.14 s (18H, CH3), 2.70–3.22m
(4H, CH2–S), 3.45–3.58m (4H, O–CH2–CH–OSi), 3.67–3.76 and
3.82–3.86m (8H, CH2CH2O), 3.95–4.01dd and 4.13–4.20dd (4H,
CH2 ), 4.25–4.41m (2H, CH–OSi), 6.42–6.51q (2H, CH ); IR (neat,
cm−1): 3117, 3046 (␯, C–H); 2924, 2900, 2873 (␯, CH, CH2);
1636–1617 (␯, C C); 1250 (ı, CH3); 1040–1180 (␯, C–O–C); 976
(ω, –CH CH2); 841 (␯, Si–C); 690, 615 (␯, S–C); 477 (␯, S–S); ele-
mental analysis calcd (%) for C20H42O6S3Si2.: C, 45.25; H, 7.97; S,
18.12; Si, 10.58; found: C, 46.00; H, 7.62; S, 17.88; Si, 9.84.
2,2,12,12-Tetramethyl-4,10-diphenyl-3,11-dioxa-6,7,8-trithia-2,
12-disilatridecane 14 was obtained according to Scheme 3 (see
Section 3).
The hydroxyorganyl polysulfide 7 (2.0 g, 5.9 mmol) was mixed
with hexamethyldisilazane (2.0 g, 12.3 mmol), and the mixture was
stirred for 48 h at room temperature. Excess of hexamethyldisi-
lazane was removed by vacuum distillation to produce 2.85 g (100%
yield) of polysulfide 14, a light-yellow viscous liquid, soluble in
diethyl ether, 1,2-dimethoxyethane and insoluble in water.
CF3CO2H
- HOEt
R
R
R
R
+
Si(OEt)4
Sn
Sn
O
O
OH
OH
(EtO)3Si
Si(OEt)3
n = 2-3
7, 10, 11
20-22
R = Ph (7, 20);
N
;
(10, 21)
(11, 22);
N
Scheme 4. Synthesis of the polysulfide 20–22.

B.A. Trofimov et al. / Electrochimica Acta 56 (2011) 2458–2463
2461
Table 1
Bis{3-(1H-pyrrol-1-yl)-2-[(trimethylsilyl)oxy]propyl}disulfide 17
Protected bis(hydroxyorganyl)polysulfides.
was synthesized from 1-(2-oxiranylmethyl)-1H-pyrrole 4 and hex-
amethyldisilazane according to Schemes 1 and 3, in 61% yield
as brown viscous liquid, soluble in diethyl ether, acetone, 1,2-
dimethoxyethane.
Polysulfide Structural formula
2-(1H-indol-1-yl)-1-[(3-{3-(1H-indol-1-yl)-2-
S3
[(trimethylsilyl)oxy]propyl}trisulfanyl)methyl]ethyl
trimethylsilyl
Me
O
O
Me
ether 18 was synthesized from 1-(2-oxiranylmethyl)-1H-indole
5 and hexamethyldisilazane according to Schemes 1 and 3 in
87% yield as brown liquid, soluble in diethyl ether, acetone,
1,2-dimethoxyethane.
OBu-n
n-BuO
13
1H NMR (CDCl3), ı, ppm: 0.23 s (18H, CH3), 2.84–3.17m (4H,
CH2–S), 4.23m (4H, CH2N), 4.47m (2H, CH–O), 6.64–7.76 (12H,
indole ring); IR (neat, cm−1): 3080, 3040, 2945 (␯, C–H, CH3);
2920, 2890, 2840 (␯, CH, CH2); 1605 (␯, C C), 1498 (␯, N–C);
1060–1080 (␯, Si–O–C; ı, indole ring); 820 (␯, Si–C); 720 (ı, indole
ring); 680 (␯, S–C); 460, 440 (␯, S–S); elemental analysis calcd (%)
for C28H40N2O2S3Si2: C, 57.10; H, 6.85; N, 4.76; S, 16.33; Si, 9.54;
found: C, 58.54; H, 7.23; N, 4.89; S 16.41; Si 8.00.
Mixed of 4,9-bis[(1,3-dioxolan-4-ylmethoxy)methyl]-2,2,11,11-
tetramethyl-3,10-dioxa-6,7-dithia-2,11-disiladodecane and 4,9-bis
[(1,3-dioxan-5-yloxy)methyl]-2,2,11,11-tetramethyl-3,10-dioxa-6,7-
dithia-2,11-disiladodecane 19 was synthesized from the mixture
of 1,3-dioxolan- and 1,3-dioxanoxiranes 6 (3:1) according to
Schemes 1 and 3 in 21% yield as brown viscous liquid, soluble in
diethyl ether, acetone, 1,2-dimethoxyethane.
S3
O
O
Me3Si
SiMe3
S3
14
15
O
O
O
O
Me3Si
SiMe3
O
O
O
Sx
x = 2-3
O
O
O
Me3Si
SiMe3
16
17
N
N
S2
The product contains 73% of dioxolane and 27% of dioxane moi-
eties, respectively.
O
O
Me3Si
SiMe3
2.3.4. The reactions of hydroxyorganyl polysulfides with
tetraethyl orthosilicate
9,9-Diethoxy-1,7-diphenyl-8,10-dioxa-3,4,5-trithia-9-siladodecyl
triethyl orthosilicate 20 was synthesized according to Scheme 3
(see Section 3).
N
N
Sx
O
O
The hydroxyorganyl polysulfide 7 (2.00 g, 5.9 mmol) was dis-
solved in 3 ml of 1,2-dimethoxyethane, then 6.50 g (31.2 mmol)
of tetraethyl orthosilicate and 0.02 ml of trifluoroacetic acid were
added. The solution was stirred for 24 h at 60 ◦C. Then, K2CO3
(0.10 g) was added to the solution, the resultant mixture was stirred
for 1 h at room temperature and filtered off. Excess of tetraethyl
orthosilicate was removed by vacuum distillation to produce 3.92 g
(100% yield) of polysulfide 20, a brown mobile liquid, soluble in
diethyl ether, 1,2-dimethoxyethane and insoluble in water.
8,8-Diethoxy-1,6-bis(1H-pyrrol-1-ylmethyl)-7,9-dioxa-3,4-
dithia-8-silaundecyl triethyl orthosilicate 21 was synthesized from
1-(2-oxiranylmethyl)-1H-pyrrole 4 and tetraethyl orthosilicate
according to Schemes 1 and 4 in 65% yield as brown, highly viscous
oil, soluble in diethyl ether, 1,2-dimethoxyethane and insoluble in
water.
Me3Si
SiMe3
x = 2-3
18
R1
O
R2
Sx
O
O
O
Me3Si
SiMe3
x = 2-3
O
,
R1, R2 =
O
O
O
19
20
S3
O
O
(EtO)3Si
Si(OEt)3
9,9-Diethoxy-1,7-bis(1H-indol-1-ylmethyl)-8,10-dioxa-3,4,5-
trithia-9-siladodecyl triethyl orthosilicate 22 was synthesized from
N
N
O
1-(2-oxiranylmethyl)-1H-indole
5 and tetraethyl orthosilicate
S2
according to Schemes 1 and 3 in 49% yield as brown, highly viscous
oil, soluble in diethyl ether, 1,2-dimethoxyethane and insoluble in
water.
O
(EtO)3Si
Si(OEt)3
21
3. Results and discussion
N
N
The reaction of oxiranes with sodium polysulfide in the presence
of sodium hydrocarbonate as a buffer was used for the synthesis of
the starting hydroxyorganyl polysulfides (Scheme 1). The hydrox-
yorganyl polysulfides have been protected at the hydroxyl group
by the reactions with N-butoxyethene (Scheme 2), hexamethyldis-
ilazane (Scheme 3) and tetraethyl orthosilicate (Scheme 4).
The protected functionalized polysulfides synthesized are listed
in Table 1.
Sx
O
O
(EtO)3Si
Si(OEt)3
x = 2-3
22

2462
B.A. Trofimov et al. / Electrochimica Acta 56 (2011) 2458–2463
3
2,5
2
3,0
b
a
2,5
2,0
1,5
1,5
1
5
2
1
10
10
5
2
1
1,0
0,5
0,5
0
200
400
600
800 1000 1200
0
200 400 600 800 1000 1200
Capacity / mAh g-1
Capacity / mAh g-1
3,5
3
3,5
3
c
d
2,5
2
2,5
2
1,5
1
1,5
1
1
5
2
1
2
1
10
5
0,5
0,5
0
200
400
600
800 1000 1200
0
200
400
600
800
1000
1200
Capacity / mAh g-1
Capacity / mAh g-1
Fig. 1. Discharge curves for Li/S cells containing three most effective additives (5 wt.%) 14 (b), 18 (c), 16 (d) in comparison with that of additive-free cell with the standard
electrolyte (a) (1st, 2nd, 5th and 10th cycles).
The addition of 5 wt.% of organic polysulfides to the standard
electrolyte (see Section 2) does not change the shape of discharge
curves in the Li/S electrochemical cell. Fig. 1 shows the discharge
curves of Li/S cells containing the three most effective additives
14, 18, 16 in comparison with that of additive-free cell: the sur-
plus of the capacity on the 5th cycles equals 27, 9 and 12% for
the additives 14, 18 and 16, respectively and the relative gain of
the capacity of the additives keeps retaining and even augment-
ing during 50th cycles (25–35% for the same additives) and further
on (Fig. 2). On the discharge curves, there are two regions at 2.35
and 2.06 V corresponding to a two-stage mechanism of the elec-
trochemical reduction of sulfur that is in agreement with literature
data [3,5,8].
Fig. 2 illustrates the cycling behavior of the cell with the
standard electrolyte and the cells with electrolytes modified
by 5 wt.% polysulfides 14 and 18. It is seen that these poly-
sulfides remain active at least up to 50th cycles and sustain
Fig. 3. The effect of polysulfides 13–22 structure on the discharge capacity of Li/S
cells (5 wt.% in the standard electrolyte). The curve numbers correspond to polysul-
fide numbers.
Fig. 2. The effect of 5 wt.% of polysulfides 14 and 18 added to the standard electrolyte
on the discharge capacity of Li/S cells during cycling.

B.A. Trofimov et al. / Electrochimica Acta 56 (2011) 2458–2463
2463
the discharge capacity always higher than that of the standard
cell.
Analysis of the relationship between the polysulfides structure
and their effect on the battery performance (Fig. 3) allows one to
divide the compounds into the three groups:
OSiMe3
O
O
O
-
Sx
Li+
1. Active additives which increase the discharge capacity up to
25–35% relative to the standard electrolyte. These are polysul-
fides 14 and 18 with trimethylsilyl protection and aromatic or
heteroaromatic (benzene or indole) moieties.
Unsubstituted 1,3-dioxolane which is a component of the bat-
tery electrolyte can be involved in this polymerization resulting in
deterioration of both electrolyte and lithium anode.
2. Additives of moderate activity giving 5–15% capacity increase
(polysulfides 13, 15–17).
4. Conclusions
3. Additives with negative effect on the battery capacity (polysul-
fides 19–22).
In conclusion, bis(hydroxyorganyl) polysulfides protected at
hydroxyl group are promising for further systematic search of the
modifiers of the Li/S battery electrolyte to improve the battery
capacity and cycling life. The presence of tri(methyl)silyl group in
the molecules of bis(hydroxyorganyl) polysulfides increases effi-
ciency of the additives in terms of the battery capacity and its
cycling life.
The higher activity of polysulfides 14 and 18 is likely caused by
a better “solubility” of the lithium mercaptides (lithium organyl
polysulfides) resulted from the insertion of Li2S and Li2S2 into
the polysulfide chain (see Section 1) and also by their ability to
coordinate the lithium cation by the neighboring oxygen atom of
trimethylsilyloxy group:
+ LiS
S3
+
S4
Li
S3
Li
O
O
O
O
SiMe3
Me3Si
SiMe3
Me3Si
Upon charging, they release the inserted extra sulfur atoms
while depositing elemental sulfur on the cathode to regen-
erate the starting additives (protected (bis)organyl)hydroxy
polysulfides).
Insoluble short-chain lithium sulfides is known to react with
long-chain lithium polysulfides to produce soluble polysulfides
[20].
Acetal-protected (13) and some other trimethylsilyl protected
hydroxypolysulfides (15–17) generally demonstrate moderate
positive effect on the standard electrolyte performance.
Triethoxysilyl group located near the polysulfide bond (polysul-
fides 20–22) diminishes the battery capacity probably due to the
reduction of the Si–O bonds with Li metal:
References
[1] M. Wada, K. Kabuki, in: J.P. Salamone (Ed.), Polymer Materials Encyclopedia,
CRC Press, New York, 1996, p. 443.
[2] B.H. Jeon, J.H. Yeon, K.M. Kim, I.J. Chung, J. Power Sources 109 (2002) 89.
[3] J.R. Akridge, Y.V. Mikhaylik, Neal White, Solid State Ionics 175 (2004) 243.
[4] Y.J. Choi, K.W. Kim, H.J. Ahn, J.H. Ahn, J. Alloys Compd. 449 (2008) 313.
[5] Y.V. Mikhaylik, J.R. Akridge, J. Electrochem. Soc. 150 (2003) A306.
[6] H.S. Ryu, H.J. Ahn, K.W. Kim, J.H. Ahn, K.K. Cho, T.H. Nam, Electrochim. Acta 52
(2006) 1563.
[7] S. Kim, Y. Jung, S.J. Park, Electrochim. Acta 52 (2007) 2116.
[8] J.W. Choi, G. Cheruvally, D.S. Kim, J.H. Ahn, K.W. Kim, H.J. Ahn, J. Power Sources
183 (2008) 441.
[9] J. Sun, Y. Huang, W. Wang, Z. Yu, A. Wang, K. Yuan, Electrochem. Commun. 10
(2008) 930.
[10] R.D. Rauh, F.S. Shuker, J.M. Marson, S.B. Brummer, J. Inorg. Nucl. Chem. 39 (1977)
1761.
[11] V. Kolosnitsyn, E. Karaseva, WO Patent 141568 (A2) (2007).
[12] N.I. Dowling, K.L. Lesage, J.B. Hyne, Alberta Sulphur Res. Ltd. Q. Bull. 21 (1984)
30.
2 Li
+
Si OEt
Si Li
LiOEt
[13] P.D. Clark, R.A. Clarke, K.L. Lesage, J.B. Hyne, Energy Fuels 2 (1988) 355.
[14] A.M. Vasil’tsov, A.I. Mikhaleva, T.A. Skotheim, B.A. Trofimov, Sulfur Lett. 22
(1999) 227.
[15] D.N. Jones (Ed.), Comprehensive Organic Chemistry, vol. 3, Sulphur compounds,
Pergamon Press, New York, 1979.
[16] Y.V. Mikhaylik, T.A. Skotheim, B.A. Trofimov, US Patent, 6569573 (2003).
[17] B.A. Trofimov, Heteroatomic Derivatives of Acetylene. New Polyfunctional
Monomers, Reagents and Intermediates, Nauka, Moscow, 1981, p. 319 (in Rus-
sian); Chem. Abstr. 96 (1982) 68296.
[18] B.A. Trofimov, L.V. Morozova, M.V. Markova, A.I. Mikhaleva, G.F. Myachina, I.V.
Tatarinova, T.A. Skotheim, J. Appl. Polymer Sci. 101 (2006) 4051.
[19] M.V. Markova, L.V. Morozova, E.Yu. Schmidt, A.I. Mikhaleva, N.I. Protsuk, B.A.
Trofimov, Arkivoc iv (2009) 57.
The behavior of the batteries with additive 19 changes upon
cycling: the capacity is higher than standard at 5–15th cycles,
approximately equal to standard at 20–40th cycle and then drops
(Fig. 3). The tentative explanation of this fact is based on the
known ability of the oxygen-containing cycles (particularly, 1,3-
dioxolanes and 1,3-dioxanes) to be polymerized under the action
of alkali metal cations [21]. The first stage of this reaction is coordi-
nation of Li+ with oxygen which may be assisted by the neighboring
polysulfide moieties, e.g.:
[20] V.S. Kolosnitsyn, E.V. Karaseva, A.L. Ivanov, Russ. J. Electrochem. 44 (2008) 564.
[21] V.R. Gowariker, N.V. Viswanathan, J. Sreedhar, Polymer Science, Wiley Eastern
Ltd., 1986.