Lithium salts of N,N′-disubstituted pentanesulfinamidines as promising additives for lithium power sources

Article abstract of DOI:10.1023/B:RJAC.0000015723.66144.e0

A procedure for preparing new lithium salts with large organic anions, which can be used as additives to nonaqueous electrolytes of high-capacity chemical power sources, was developed. The electrochemical properties of the salts were studied.

Full text of DOI:10.1023/B:RJAC.0000015723.66144.e0

Russian Journal of Applied Chemistry, Vol. 76, No. 10, 2003, pp. 1611 1614. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 10, 2003,
pp. 1653 1657.
Original Russian Text Copyright
2003 by Koval’, Shembel’, Chervakov, Oleinik, Globa.
APPLIED ELECTROCHEMISTRY
AND CORROSION PROTECTION OF METALS
Lithium Salts of N,N -Disubstituted Pentanesulfinamidines
as Promising Additives for Lithium Power Sources
I. V. Koval’, E. M. Shembel’, O. V. Chervakov, T. G. Oleinik, and N. I. Globa
Ukrainian State Chemical Engineering University, Dnepropetrovsk, Ukraine
Enerl Inc., Florida, The Unites States
Received May 6, 2003
Abstract A procedure for preparing new lithium salts with large organic anions, which can be used as ad-
ditives to nonaqueous electrolytes of high-capacity chemical power sources, was developed. The electro-
chemical properties of the salts were studied.
Solutions of inorganic lithium salts in pure aprotic
solvents or their mixtures are widely used as electro-
lytes in lithium power sources intended for different
purposes.
ically stable up to 4.8 V (relative to lithium reference
electrode) [2].
The lithium salt of bis(trifluoromethanesulfonyl)-
imide and its structural analogues LiN(SO2CF2CF3)2,
LiN(SO2C4F9)2, LiN[(CF3SO2)(C4F9SO2)] are also
used for preparing polymeric electrolytes. The anion
size in these lithium organic salts can strongly affect
the structural and electrochemical properties of poly-
meric electrolytes derived from these salts [4].
Recently researchers’ efforts have been focused on
development of procedures for preparing new, cheap,
nontoxic, moisture- and heat-resistant, and chemically
and electrochemically stable salts readily soluble in
aprotic solvents [1]. This is due to necessity for im-
provement of the performance of primary and, es-
pecially, secondary lithium-metal and lithium-ionic
batteries.
Lithium salt of bis(trifluoromethanesulfonyl)imide
LiN(SO2CF3)2 was prepared from bis(trifluorometh-
anesulfonyl)imide, which is a relatively strong NH
acid forming a stable N-anion owing to the presence
of two electron-acceptor trifluoromethanesulfonyl
groups. Bis(trifluoromethanesulfonyl)imide is not read-
ily available, since substitution of chlorine atoms in
the trichloromethyl groups with fluorine [16] requires
special equipment and conditions that are difficult to
provide in a common chemical laboratory. Alternative
components of polymeric electrolytes are lithium salts
of aromatic bis(sulfonyl)imides and, in particular, bis-
( p-nitrobenzenesulfonyl)imide ( p-NO2C6H4SO2)2NH,
which is also a relatively strong acid, pKa 3.2 (aque-
ous solution) [17].
The physicochemical properties of lithium organic
salts depend on their chemical structure: the nature
of the atom to which lithium is bonded and the type
of this bond [2]; the nature and size of the anion;
the degree of delocalization of the negative charge,
which affects the stability of the salt anion [1].
The anion affects the properties of a nonaqueous
electrolyte and of lithium power sources for the follow-
ing reasons. In aprotic solvents, anions are solvated
by dipole dipole interactions which depend on mutual
polarization of the anion and the solvent molecules.
As the size of the organic anion increases, the polari-
zation becomes stronger, thus enhancing the interac-
tion between the anion and the solvent molecule [3].
The structure and acid properties of N,N - bisarene-
sulfonyl substituted imides of iminosulfinic acids are
similar to those of aromatic bis(sulfonyl)imides [18].
These compounds inhibit thermooxidative degradation
of polymers [19], which is important for electrolytes
derived from halogen-containing polymers (polyvinyl
chloride, polyvinylidene chloride, polyvinylidene fluo-
ride, etc.).
Among the known lithium organic salts, lithium salt
of bis(trifluoromethanesulfonyl)imide LiN(SO2CF3)2
is the most promising as electrolyte for lithium
power sources [4 15]. Liquid solutions of this salt
have high electrical conductivity and are electrochem-
1070-4272/03/7610-1611 $25.00 2003 MAIK Nauka/Interperiodica

1612
KOVAL’ et al.
In this study, we prepared lithium salts of N,N -bis-
tion at 24 2 C on a pH-121 millivoltmeter with
an automated titration unit. Glass ESP/41-G-04 elec-
trode served as working electrode, and a silver chlo-
ride electrode, as reference electrode. A 0.1 M solu-
tion of Ia was titrated with 0.1 M KOH.
(benzenesulfonyl)pentanesulfinamidine and N,N -bis-
( p-toluenesulfonyl)pentanesulfinamidine and analyzed
these salts as additives to liquid and polymeric elec-
trolytes of lithium power sources.
The electrical conductivity of these salts in non-
aqueous electrolytes was measured and the range of
electrochemical stability of these solutions was de-
termined. The behavior of the modified electrolytes
in model secondary lithium power sources Li MnO2
and Li V6O13 was studied.
EXPERIMENTAL
N, N -Bis(benzenesulfonyl)pentanesulfinamidine
and its lithium salt were prepared by the following
procedures.
N, N -Bis(benzenesulfonyl)pentanesulfinamidine
(Ia). To a solution of dipentyldisulfide (0.001 mol) in
acetone (10 ml), sodium salt of N-chlorobenzenesul-
fonamide (0.0042 mol) was added. The mixture was
shaken for 30 min, allowed to stand for 12 15 h to
negative reaction for available chlorine, and filtered.
The solvent was evaporated, and the residue was
treated with 10% NaHCO3 (20 ml) and filtered. Com-
pound Ia (0.18 g, 43.9%) was isolated from acidified
filtrate. The product was identified by melting point
(mixing with an authentic sample) and by IR spec-
troscopy.
The electrical conductivity of solution of the lith-
ium salts in aprotic organic solvents was measured by
impedance spectroscopy in a temperature-controlled
glass electrochemical cell with parallel platinum elec-
trodes. The measurements were performed at a work-
ing frequency of 80 kHz and temperature of 24 2 C.
1
The electrolyte conductivity (S cm ) was calculated
by the equation
= KG,
where G is the conductance of the electrolyte in
the cell (S), and K is the cell constant determined
Compound Ib was prepared similarly in 45.4%
yield.
1
using 0.01 M aqueous solution of KCl (cm ).
Lithium salt of N,N -bis(benzenesulfonyl)pentane-
sulfinamidine (IIa). To a solution of Ia (0.001 mol)
in acetone (10 ml), equimolar amount of LiOH dis-
solved in a minimal volume of methanol or water was
added. The reaction mixture was shaken for several
minutes and filtered. The solvent was removed in air.
The residue was dried to constant weight in a desic-
cator over CaCl2. Compound IIa was obtained in
the form of a colorless powder decomposing at 88
90 C.
The range of electrochemical stability of the lithi-
um salts was determined by cyclic voltammetry under
potentiodynamic conditions. The experiment was per-
formed under an argon atmosphere in a three-electrode
Teflon cell of disc design, containing working, refer-
ence, and auxiliary electrodes. The reference and aux-
iliary electrodes were made of metallic lithium. A plat-
3
inum plate with surface area of 8.0 10 cm2 was
used as working electrode. The electrode potential was
set with a PI-50-1.1 potentiostat and a PR-8 program-
1
mer. The sweep rate was 20 mV s . The cyclovolt-
Found (%): N 6.34
C17H21N2O4S3Li.
ammograms were recorded on a PDA-1 XY-recorder
in the potential range from 1.1 to 4.6 V.
Calculated (%): N 6.66.
Polymeric electrolytes (PEs) were prepared on glass
supports from THF solutions containing a polymer,
lithium salt, and additive (synthesized lithium salt with
organic cation). The PE films were dried for 24 h at
room temperature and for 48 h in a vacuum at 45 C.
Salt IIb was prepared similarly in quantitative
yield in the form of a colorless powder decomposing
at 147 150 C.
Found (%): N 6.12
C19H25N2O4S3Li.
Charging discharge cycling of the model lithium
power sources with polymeric electrolytes containing
the synthesized lithium organic salts was performed in
the geometry of 2325 disc battery. The electrode struc-
ture was obtained by layer-by-layer application of
the polymeric electrolyte between lithium anode and
cathode. The thickness of the polymeric electrolyte
and the lithium anode was 0.03 and 0.8 mm, respec-
Calculated (%): N 6.25.
The IR spectra (KBr pellets) were recorded on
a UR-20 spectrophotometer.
The dissociation constant pKa of IIa in a 1% meth-
anol solution was determined by potentiometric titra-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 10 2003

LITHIUM SALTS OF N,N -DISUBSTITUTED
tively. The cathode was prepared from a mixture of
1613
chemically synthesized MnO2 or V6O13 (80 wt %),
carbon (5 wt %), graphite (5 wt %), and F-4D fluoro-
plastic binder (10 wt %).
N, N -Bis(benzenesulfonyl)pentanesulfinamidines
were obtained using the known modified procedure
[20]. Dipentyl disulfide was oxidatively iminated
with sodium N-chloroarenesulfonamide in acetone
by the reaction
Fig. 1. Cyclic voltammogram of 0.5 M solution of lithium
salt IIa in PC. Sweep rate 20 mV s (I) Current and
1
(V) voltage.
NSO2 Ar
C5H11
S
(C5H11S)2 + 4ArSO2NNaCl
_
4NaCl
NHSO2 Ar
Ia, Ib
Compounds Ia and Ib were indetified by melting
points (mixing with known samples), by determining
the neutralization equivalent, and by IR spectroscopy.
These compounds are relatively strong NH acids
(pKa of Ia is 2.91), which can be titrated with an al-
kali in alcoholic solution in the presence of Meth-
yl Red as indicator. The equivalent weight determined
by titration agrees with the calculated data. The IR
spectra of Ia and Ib contain the bands of stretching
vibrations of the SO2 (1160 1158 and 1310
Fig. 2. Specific capacity C of Li/PE/MnO system in
2
a 2325 battery vs. the number of charging discharge cycles.
PE composition: (a) c-PVC : PC : LiCF SO = 19.2 : 75.1 :
1
1
3
3
1335 cm ) S=N (753 765 cm ), CH3 (2925
5.7 and (b) c-PVC : PC : LiCF SO : IIa = 18.1 : 72.5 :
3
= I
3
1
1
2950 cm ), CH2 (2841 2850 cm ), and CH (ar.)
3.1 : 6.3. (n) Cycle no. I
= 100 A.
charge
discharge
1
(1485 1533 cm ) groups. Two strong bands in the
range 3250 3360 cm are assigned to N H stretching
1
1
1
and 1310 1330 cm ) and S=N (1030 1040 cm )
groups and bands of other groups. The NH bands are
absent.
vibrations. This type of absorption by the N H bonds
is due to prototropic tautomerism in the N S N triad,
which has been found previously in N,N -bis(arene-
sulfonyl)sulfinamidines [18].
Salts IIa and IIb are readily soluble in aprotic sol-
vents.
The lithium salts were prepared by neutralization
of appropriate pentanesulfinamidines with equimolar
amounts of LiOH in acetone methanol water mix-
ture [21]:
The conductivity of a 0.24 M solution of IIa in di-
methylformamide and 0.5 M solution of IIb in propyl-
ene carbonate (PC) is 6.0 10 3 and 5.2 10 4 S cm ,
1
respectively.
NSO2 Ar
Ia, Ib + LiOH
C5H11
S
Li+
Cyclic voltammograms of a 0.5 M solution of IIa
in PC, recorded on a platinum electrode under poten-
tiodynamic conditions, are shown in Fig. 1. As seen
from Fig. 1, this compound is stable under conditions
of repeated potential sweeping in the range 1.1 4.6 V.
_
H2O
NSO2 Ar
IIa, IIb
where Ar = Ph (a), p-MeC6H4 (b).
The solvents were evaporated in air, and the residue
was dried in a desiccator over CaCl2. IIa and IIb
were obtained in the form of colorless hygroscopic
powders or oily substances decomposing in a wide
temperature range.
Since this additive is electrochemically stable in
a wide potential range, it can be used in lithium power
sources with different discharge voltages: 3.8 (lithi-
um ionic systems), 2.8 (lithium metal secondary sys-
tems with oxide cathode), and 1.8 V (lithium metallic
systems with sulfide cathode).
The composition and structure of salts IIa and IIb
was confirmed by elemental analysis and IR spectros-
copy. The IR spectra of these compounds contain the
bands of stretching vibrations of the SO2 (1160 1165
We used salt IIa as a modifying additive to PE
based on chlorinated polyvinyl chloride (c-PVC) or
vinylidene fluoride hexafluoropropylene copolymer.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 10 2003

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KOVAL’ et al.
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(1) Lithium salts of N,N -bis(benzenesulfonyl)pen-
tanesulfinamidine and N, N -bis( p-tolyenesulfonyl)
pentanesulfinamidine were synthesized.
(2) The electrical conductivity of nonaqueous so-
lutions of these salts is relatively high even at low
salt concentration . The conductivity of a 0.24 M so-
lution of IIa in dimethylformamide and 0.5 M solu-
3
tion of IIb in propylene carbonate is 6.0 10 and
4
1
5.2 10 S cm , respectively.
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nesulfinamidine can be used as additive to polymeric
electrolytes to stabilize the discharge properties and
decrease the self-discharge of lithium power
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ACKNOWLEDGMENTS
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The authors are grateful to O.V. Kolomoets and
I.M. Maksyuta for studying the conductivity and elec-
trochemical stability of the electrolytes.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 10 2003