ISSN 0012-5008, Doklady Chemistry, 2007, Vol. 414, Part 1, pp. 125–127. © Pleiades Publishing, Ltd., 2007.Original Russian Text © B.A. Trofimov, A.G. Mal’kina, I.A. Dorofeev, G.F. Myachina, I.V. Rodionova, T.I. Vakul’skaya, L.M. Sinegovskaya, T.A. Skotheim, 2007, published inDoklady Akademii Nauk, 2007, Vol. 414, No. 2, pp. 204–206.

125

In recent decades, the design of Li/S batteries hasbrought about interest in highly sulfurous redox com-pounds as active components of cathodic compositions[1–5]. Recently [6], while searching for approaches toelectroconductive polymers with thiol, thione, andpolysulfide functions, we developed a method for thepreparation of polyene polysulfides derived from acet-ylenic monothiols (ethynethiols and ethynehydro-polysulfanes) based on the reaction of sodiummonoacetylenides with elemental sulfur in liquidammonia.

In this work, we give a brief account of the synthesisand properties of a new group of polyeneoligosulfides,

ethynedithiol oligomers, which are promising activecomponents of Li/S batteries.

Oligomers containing blocks

5

–

7

were prepared byspontaneous oligomerization of ethynedithiol

2

and itstautomers

3

and

4

. Thiol

2

was generated by hydrolysisof sodium ethynedithiolate

1

prepared from acetylene,elemental sulfur, and sodium metal in liquid ammoniaaccording to Brandsma [7]. All process steps startingfrom the synthesis of dithiolate

2

and ending with oli-gomerization of compounds

2

–

4

are performed in theone-pot mode.

S

SH SH

SHS

SH

SH

SH

HC≡CH HC≡CNa HC≡CSNa NaC≡CSNa

NaSC≡CSNa HSC≡CSH HSC=C=S S=CH–CH=S

Na/NH3

1/8S8

Na/NH31/8S8

H2O/H+

spontaneousoligomerization

1 2 3 4

5 6 7

The yield of oligomers depends on the synthesisconditions, way of processing of reaction mixtures, andpurification of the isolated products and reaches at best96% (per repeating unit). The isolated oligomers aremixed with products of their transformations, dithi-

olene blocks

8

and

9

(formed upon oxidation of thethiol functions by atmospheric oxygen):

On treatment of the oligomers with hot xylene, oli-gothienothiophene structure

10

can also be formed(through desulfurization of blocks

7

–

9

):

S

S S

SS

S S

SH

5–7oxidation

(air)–H2O

8 9

oxidation(air)

–H2O

Ethynedithiol Oligomers as Cathode Components of Lithium–Sulfur Batteries

Academician

B. A. Trofimov

a

, A. G. Mal’kina

a

, I. A. Dorofeev

a

, G. F. Myachina

a

, I. V. Rodionova

a

, T. I. Vakul’skaya

a

, L. M. Sinegovskaya

a

, and T. A. Skotheim

b

Received December 20, 2006

DOI:

10.1134/S0012500807050060

a

Favorsky Institute of Chemistry, Siberian Division, Russian Academy of Sciences, ul. Favorskogo 1, Irkutsk, 664033 Russia

b

Intex, 7080 Cathedral Rock Pl., Tucson, AZ 85718, USA

CHEMISTRY

126

DOKLADY CHEMISTRY

Vol. 414

Part 1

2007

TROFIMOV et al.

The resulting oligomers are brown powders contain-ing 52–77% sulfur with melting points from 120 to

200°ë

partially soluble in organic solvents. The IRspectra of the oligomers show a broad poorly resolvedband with peaks at 1476–1453, 1435–1432, 1413–1408, and 1367–1325 cm

–1

for the polyene–polythioland polyene–polysulfide blocks

7

–

9

and the poly-thienothiophene core

10

[4]. The peaks at 1290–1280,1250–1221, and 1200–1149 cm

–1

correspond to theC=S group of structures

6

–

8

[8, 9]. The low diffusepeaks at 856–802, 790–730, 691–606, and 592–547 cm

–1

refer to the C–S stretching vibrations of vari-ous polymer fragments [10, 11]. All polymers areresponsible for weak peaks at 485–412 cm

–1

due to theS–S vibrations of the dithiolene blocks and di- and oli-gosulfide fragments of structures

8

and

9

[8, 9].

The oligomers have a specific conductivity of about

10

–13

–10

–14

S/cm and show an intense EPR signal (

10

17

–10

18

spins/g,

g

= 2.0043–2.0072), which attests to thepresence of structural blocks

5

,

9

,

and

10

with anextended conjugation system.

The cyclic voltammograms of the oligomers (Fig. 1)confirm the presence of di- and polysulfide bonds(blocks

8

and

9

). They exhibit typical stepwise reduc-tion of the polysulfide fragments with peaks at 2.5 and1.8 V vs.

Li/Li

+

. The subsequent oxidation of the result-ing lower lithium sulfides occurs at potentials of2.4

−

2.5 V.

Typical variation of the specific discharge capacityof ethynedithiol oligomer-based cathodes on cycling inlithium batteries is shown in Fig. 2.

S

S

n

7–9–H2S, S

10

The sharp decrease in the capacity observed in thefirst cycles is due to partial irreversible migration of thesulfide and polysulfide anions from the cathode surface,which is a usual problem of Li/S batteries. As followsfrom Fig. 2, the oligomers are able to ensure stablecycling of a lithium battery at rather high capacities.These oligomers are promising as active binding agentsfor cathodic compositions based on elemental sulfur.They can be expected to operate as an active matrixretaining the polysulfide anions in the cathodic area.

Thus, the proposed synthetic strategy for the prepa-ration of new conductive redox oligomers(ethynedithiol derivatives) can be used for furtherimprovement of Li/S battery characteristics.

IR spectra were recorded on a Bruker IFS 25 spec-trophotometer (KBr pellets). EPR spectra were mea-sured on Radiopan SE/X-2547 spectrometer. Electricalconductivity was measured on an E6-13A teraohmme-ter. Voltammograms were recorded on a PI-50-1 poten-tiostat. Cell cycling was carried out at a current densityof 0.25 mA/cm

2

in the voltage range 1.25–2.80 V on ameasuring test bench for chemical batteries.

Typical procedure of the synthesis ofethynedithiol oligomers.

Sulfur (1.60 g, 0.05 mol) wasadded over a period of 40 min to sodium acetylenideprepared from sodium (1.15 g, 0.05 mol) in liquidammonia (500 mL). After stirring for 2 h, a second por-tion of sodium (1.15 g, 0.05 mol) was added and themixture was stirred for 1 h. Then, sulfur (1.60 g,0.05 mol) was added over a period of 40 min. The mix-ture was stirred for 3 h, two-thirds of the ammonia vol-ume was removed, and the mixture was poured intocooled 10% hydrochloric acid (100 mL). The hydroly-sis product was kept at room temperature for 12 h. Theoligomer thus formed was filtered off; washed withwater (until no Cl

–

was detected), acetone, and ether;and dried in vacuum for 6 h at room temperature. This

0.5 mA

1

6

1

6

1 2 3

E

, V200

0 5

Q

,

mA h/g

Cycle number

800

10

600

400

15 20 25 30

Fig. 1.

Typical voltammogram of ethynedithiol oligomers.

Fig. 2.

Specific discharge capacity (

Q

) of the cathode basedon ethynedithiol oligomer (

S

= 77%) on cycling in a lithiumbattery.

DOKLADY CHEMISTRY

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ETHYNEDITHIOL OLIGOMERS AS CATHODE COMPONENTS 127

gave 4.30 g (95.6% based on ethynedithiol) of the prod-uct as a brown powder, mp 128–130

°

C.For C

2

H

2

S

2

anal. calcd. (wt %): S, 71.1.Found (wt %): S, 69.3.

ACKNOWLEDGMENTS

This work was supported by the Council for Grantsof the President of the Russian Federation for Supportof Leading Scientific Schools (grant no. NSh–5444.2006.3).

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