ORI GIN AL PA PER

Electrochemical properties of poly(4,40-diaminodiphenyl sulfone) as a cathode materialof lithium secondary batteries

Su-Ryeon Yun • Kwang Man Kim • Jang Myoun Ko •

Yongku Kang • Kwang Sun Ryu

Received: 4 September 2012 / Revised: 3 March 2013 / Accepted: 21 July 2013 /

Published online: 10 August 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract Doped poly(4,40-diaminodiphenyl sulfone) (pDDS) is prepared for use

as a cathode-active material of lithium secondary batteries by chemical oxidation

method using ammonium persulfate initiator. The synthesized pDDS and doped

pDDS are characterized by chemical structure analysis using Fourier-transform

infrared spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry

shows that the doped pDDS has a typical pair of redox peaks at 3.75/3.15 V vs. Li/

Li?, corresponding to charging/discharging of the lithium ion. The discharge

capacity at low current rate (0.05 C-rate) achieves 31.5 and 24.3 mA h g-1 in the

initial and 50th cycles, respectively. The doped pDDS also shows good cycle per-

formance and high-rate capability, making it appropriate as a cathode material of

lithium secondary batteries.

Keywords Poly(4,40-diaminodiphenyl sulfone) � Cathode material �Electrochemical property � Lithium secondary battery

S.-R. Yun � K. S. Ryu (&)

Department of Chemistry, University of Ulsan, Ulsan 680-749, Republic of Korea

e-mail: ryuks@ulsan.ac.kr

K. M. Kim

Power Control Devices Team, Electronics and Telecommunications Research Institute (ETRI),

Daejeon 305-700, Republic of Korea

J. M. Ko

Division of Applied Chemistry and Biotechnology, Hanbat National University, Daejeon 305-719,

Republic of Korea

Y. Kang

Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejeon 305-600,

Republic of Korea

123

Polym. Bull. (2013) 70:3011–3018

DOI 10.1007/s00289-013-1003-3

Introduction

Since the emergence of conducting polymers, their practical use as active electrode

materials in energy storage devices has been the goal. Conventional conducting

polymers such as polyaniline, polypyrrole, and polythiophene partly succeed in

coin-type Li polyaniline cells, but eventually fail during use due to lower energy

densities (gravimetric and volumetric). This result is expected based on the low

doping ratio of lithium salt and the need for enlarged electrolyte solution [1]. The

study of conducting polymers is focused on conducting polymer derivatives to serve

as optimal electrode materials.

Newly developed conducting polymers, such as polymer of diphenyl sulfone

derivatives, have been studied due to their excellent electronic and mechanical

properties, solution or melt processability, and high environmental stability for

applications such as antibiology [2], electrochromicity and creating compatible

joints with mechanical strength. Of these, 4,40-diaminodiphenyl sulfone (DDS)

monomer and poly(DDS) (pDDS) have been synthesized and structurally analyzed

[3–9]. The pDDS appears particularly promising as a material in electrochromicity

with enhanced adherent characteristics [4], as an energy storage device such as a

capacitor [10] and a promotion agent for photocatalytic reactions [11], due to its

higher conductivity and good solubility in organic compounds such as N,N-dimethyl

formamide and dimethyl sulfoxide. In this respect, it is expected that the pDDS can

be adopted as an electroactive materials by utilizing its high conductivity.

Therefore, it is of interest to examine the electrochemical properties of pDDS as

a cathode-active material of lithium secondary batteries.

In this work, pDDS is prepared by polymerization during a chemical oxidation

process from DDS. The pDDS is applied for the first time to a cathode-active

material in lithium secondary batteries. The resulting pDDS is expected to contain

aniline bonds divided by –S– bonds that are confined along the polymer chains.

Chemical analysis of pDDS is compared with a polyaniline structure to identify the

incorporation of –N–N– links in the chain backbone. Finally, the pDDS electrode

containing aniline and O=S=O groups is fabricated, and its electrochemical

properties including redox behavior and charge/discharge profiles for repeated

cycles are investigated for use as a cathode material of lithium secondary batteries.

Experimental

The 4,40-diaminodiphenyl sulfone monomer (C12H10O2N2S, 99 %) was dissolved in

1 M HCl solution at 80 �C in a N2 atmosphere. Ammonium persulfate ((NH4)2S2O8,

98 %) was used as a redox initiator. The initiator solution was slowly added using a

dropping funnel to the reactant solution while stirring vigorously. The reaction

mixture was then agitated continuously for 24 h under N2 atmosphere at 80 �C. The

precipitated particles were filtered and washed with hot distilled water to remove

any impurities. The filtered product containing HCl-doped pDDS was dried under

vacuum for 48 h to yield a dry powder. The powder was then reduced by excess

solution of 1 M NH4OH to give dedoped pDDS (or pDDS). The pDDS was treated

3012 Polym. Bull. (2013) 70:3011–3018

123

again for doping in 1 M HCl solution and finally dried under vacuum for 12 h to

produce HCl-doped pDDS (or doped pDDS).

The synthesized polymers (pDDS and doped pDDS) were characterized by surface

group analysis using a Fourier-transform infrared spectrometer (Varian 2000) in the

wavenumber range of 4,000–400 cm-1. X-ray photoelectron spectroscopy was

performed on the synthesized polymer powders using a VG ESCALAB Mk(II)

spectrometer (A1 Ka 1486.6 eV photons). The neutral peak of carbon 1s (C1s) at

284.6 eV was used as a reference to correct the shift by surface-charging effects.

A coin-type cell (2032) was fabricated in a dry box for investigation of the

electrochemical property. Lithium foil was used as a negative electrode. The doped

pDDS (90 wt%) as the positive electrode was mixed with carbon black (Super P,

Timcal, 5 wt%) as a conductive agent and poly(vinylidene fluoride) (Aldrich, 5 wt%)

as a polymer binder. The electrolyte solution used was 1.15 M LiPF6 dissolved in

ethylene carbonate/ethylmethyl carbonate/dimethyl carbonate (3/2/5 weight basis).

Cyclic voltammetry was performed on the Li pDDS cell using a potentiostat

(WBCS3000, WonA Tech) within the potential range of 2.0–4.5 V (vs. Li/Li?) at the

scan rate of 0.05 mV s-1. Galvanostatic charge and discharge were also carried out for

50 cycles using a cycler (WBCS3000, WonA Tech) in the voltage range of 2.5–4.0 V

at a constant current density of 8 mA g-1, practically corresponding to a 0.05 C-rate.

In addition, the rate-capability test was performed by varying the C-rate every seven

cycles to 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 5.0, and 0.1 C-rates.

Results and discussion

Figure 1 shows the Fourier-transform infrared spectra of the pDDS and doped

pDDS. Though slight deviations are appeared, the pDDS and doped pDDS exhibit

similar characteristic bands of stretching and bending vibrations for the surface

groups such as N–H, C=C, C–H, and S=O. Compared with the previous reports [4,

7, 10, 12], most of the bands observed for the present pDDS and doped pDDS are

shifted. Nonetheless, the band identifications for the doped pDDS in Fig. 1 may be

summarized as follows: N–H stretchings at 3,596 and 3,363 cm-1, N–H bending at

1,634 cm-1, C=C stretchings of quinoid and benzenoid rings at 1,588 and

1,503 cm-1, respectively, C=C bending vibration at 692 cm-1, S=O stretchings at

1,298 and 1,149 cm-1, S=O bending at 567 cm-1, C–H in-plane bending at

1,102 cm-1, and C–H out-of-plane bending at 832 cm-1. Particularly, the bands at

1,302 and 555 cm-1 [7] corresponding to S=O stretching and S=O bending modes,

respectively, shift their frequency and intensity in the present pDDS to 1,298 and

567 cm-1, respectively.

On the other hand, it is difficult to distinguish the pDDS and doped pDDs in the

Fourier-transform infrared spectra in Fig. 1 due to the similar intensities and

frequencies of each band peak. However, the effect of HCl- or H?-doping may be

observed by the decrease in the absorption intensity of N–H stretching vibrations at

3,596 and 3,363 cm-1 due to slight shrinkage by an attack of H? to a part of –N=,

resulting in the formation of an N? group in the main chain. The H?-doping can be

confirmed by the N1s X-ray photoelectron spectroscopy results (see Fig. 2). The

Polym. Bull. (2013) 70:3011–3018 3013

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pDDS possesses two peaks corresponding to –N= and –NH–, centered at 399.5 and

402.9 eV, respectively. The percentage of peak area ratio or Lorentzian-Gaussian is

estimated to be 53.2 and 46.8 % for the –N= and –NH–, respectively. Meanwhile,

the H?-doped pDDS includes three peaks corresponding to –N=, –NH–, and N?

centered at 398.7, 399.7, and 401.3 eV, respectively. The percentage of peak area

ratio due to the positive nitrogen (N?) is 46.0, 44.0, and 10.0 % for the –N=, –NH–,

and N?, respectively. This implies generation of charged nitrogen sites by H?-

doping with the decrease in the peak area ratio percentages of –N= and –NH–.

These results reflect the doping/dedoping structure of pDDS, as shown in Fig. 3a.

Also, the charging/discharging mechanism of pDDS (Fig. 3b) can be expected to

occur in association with the doping/dedoping process.

The cyclic voltammogram of the Li-doped pDDS cell is shown in Fig. 4, recorded

at a scan rate of 0.05 mV s-1. It may be confused by the fact that the potential range in

Fig. 4 is 2.0–4.5 V vs. Li/Li?, whereas the previous reports range from -0.2 V to 0.8

or 1.2 V in 0.1 M H2SO4 [4, 5] or 0–0.9 V vs. Ag/AgCl [8]. In this study, only redox

behavior within the doped pDDS electrode is considered for Li? transport, as shown in

Fig. 3b. Unlike a charge separation mechanism [13], the Li? transferred from the

lithium metal anode or the electrolyte solution interacts with the negative oxygen (O-)

on one side of the O=S=O group during the charging process, resulting in an oxidative

broad peak at 3.75 V in Fig. 4. During discharge process, the Li? dissociates with the

negative oxygen, transforming into the original O=S=O group to yield the reductive

peak at 3.15 V in Fig. 4. The charging/discharging process, which corresponds to a

typical pair of peaks at 3.75/3.15 V, is seen to be reversible. However, another

reductive peak at 2.4 V seems to be partially due to a charge separation mechanism,

i.e., the reduction in a small portion of positive N [13].

The charge and discharge profiles in Fig. 5a for doped pDDS may be an evidence

of the peak potentials described above. The charge profile of the doped pDDS shows

a breakpoint at 3.75 V, observed by a very small plateau, corresponding to the

oxidative peak at 3.75 V in the cyclic voltammogram. The oxidation peak at 3.75 V

reflects a physical interaction between Li? and O- in the main chain, which may be

formed temporarily. Thus, the charging profile looks like a smooth curve with a

3500 3000 2500 2000 1500 1000 500

1634

1588 1503

1298

33633596

1149

1102 832

692567

(b) Doped pDDS

Tra

nsm

ittan

ce (

a.u.

)

Wavenumber (cm-1)

(a) pDDS

Fig. 1 Fourier-transforminfrared spectra of the a pDDSand b doped pDDS

3014 Polym. Bull. (2013) 70:3011–3018

123

small breakpoint at 3.75 V. A plateau can be clearly observed if a chemical and/or

an electrochemical reaction such as intercalation/deintercalation or alloying/

dealloying occurs. It may be similar with the description in the case of the

reduction peak at 3.15 V.

In terms of electrochemical performance, the specific discharge capacity of the

doped pDDS achieves 31.5 and 24.3 mA h g-1 at initial and 50th cycles,

respectively. A very large irreversible capacity between charge and discharge

during the initial cycle arises by initial absorption of large excess Li?, which is

overcharged even at the inactive sites. However, the cycle performance after the

first charging process is moderately stable by the fact that the capacity retention

ratio at the 50th cycle reaches about 77 % (see Fig. 5b). This may be due to the

stability of the charging/discharging process, which is supported by structural

stability of the doped pDDS connected with aniline and sulfone moieties in series.

As shown in Fig. 6, the high-rate capability result also shows a superior

performance. For instance, the recovery ratio at 0.1 C-rate after 50 cycles through

various severe current rates from 0.1 to 5.0 C-rates becomes almost 100 %. The

recovery ratio can also reflect the excellent cycle performance discussed above.

Such recovery is a characteristic feature of pDDS as a cathode-active material in

lithium secondary batteries with high-power requirements.

Fig. 2 N1s X-ray photoelectroncore spectra of the a pDDS andb doped pDDS

Polym. Bull. (2013) 70:3011–3018 3015

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Conclusions

This paper describes for the first time the characterization of doped pDDS for use as

a cathode-active material in lithium secondary batteries. The doped pDDS is

structurally identified by the polymer in which the aniline and sulfone moieties are

repeatedly connected in series in the main chain, providing sufficient structural

stability to endure many cycles of charge and discharge at high current rates. Even

Fig. 3 Reaction mechanisms of a doping/dedoping in the pDDS material and b charging/discharging inthe doped pDDS electrode

2.0 2.5 3.0 3.5 4.0 4.5-10

-5

0

5

10

15

ReductionCur

rent

den

sity

(m

A-1

g)

Potential (V)

1

2

1

2

Oxidation

Scan rate

0.05 mV s -1

Fig. 4 Cyclic voltammogramof the doped pDDS electrode,obtained at 0.05 mV s-1. Thenumber in the figure indicatescycle numbers

3016 Polym. Bull. (2013) 70:3011–3018

123

though the specific discharge capacity is comparatively low (about 30 mA h g-1),

the doped pDDS can be considered as a promising candidate for cathode-active

material in lithium secondary batteries due to its cycle performance and high-rate

capability in applications.

0 10 20 30 40 50 60 70 802.5

3.0

3.5

4.0

Vol

tage

(V

)Specific capacity (mAh g-1)

@0.05 C-rate1

50

1030

(a)

0 10 20 30 40 500

10

20

30

40

Spe

cific

dis

char

ge c

apac

ity (

mA

h g-1

)

Cycle number

(b)

Fig. 5 a Charge and dischargecurves and b cyclic performanceof the doped pDDS electrode at0.05 C-rate. The number in thefigure indicates cycle numbers

0 10 20 30 40 500

5

10

15

20

25

30

0.1C

5.0C3.0C

2.0C

1.0C

0.5C

0.2C

Spe

cific

dis

char

ge c

apac

ity (

mA

h g-1

)

Cycle number

0.1C

Fig. 6 Rate-capability resultsof the doped pDDS electrode

Polym. Bull. (2013) 70:3011–3018 3017

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Acknowledgments This research was supported by a grant from the Fundamental R&D Program for

Core Technology of Materials funded by the Korean Ministry of Knowledge Economy and by the Priority

Research Centers Program through the National Research Foundation of Korea (NRF) funded by the

Ministry of Education, Science and Technology (2009-0093818).

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