Efficient charge transport of a radical polyether/SWCNT composite electrode for an organic radical battery with high charge-storage density

Article abstract of DOI:10.1039/c4ra15949g

A crosslinked poly(4-glycidyloxy TEMPO) was synthesized via anionic ring-opening copolymerization of 4-glycidyloxy TEMPO and a diglycidyl ether using a pentaerythritol/phosphazene base initiator. A fast and reversible charge storage capability was established for the polyether/SWCNT composite layer with a large layer thickness of several tens of micrometres, despite the low SWCNT content of 10% which was much closer to the percolation limit than the amount required for the previously reported TEMPO-substituted polymethacrylate. This journal is

Full text of DOI:10.1039/c4ra15949g

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Efficient charge transport of a radical polyether/
SWCNT composite electrode for an organic radical
battery with high charge-storage density†
Cite this: RSC Adv., 2015, 5, 15448
Received 8th December 2014
Accepted 26th January 2015
*
*
Takashi Sukegawa, Kan Sato, Kenichi Oyaizu and Hiroyuki Nishide
DOI: 10.1039/c4ra15949g
www.rsc.org/advances
A crosslinked poly(4-glycidyloxy TEMPO) was synthesized via anionic ionic and electronic (or mixed) conductor and a binder within
ring-opening copolymerization of 4-glycidyloxy TEMPO and a digly- the cathode layer.33,34
cidyl ether using a pentaerythritol/phosphazene base initiator. A fast
We have been pursuing organic radical-containing polymers
and reversible charge storage capability was established for the as electrode-active materials in organic secondary batteries
polyether/SWCNT composite layer with a large layer thickness of which are characterized by the excellent electrochemical prop-
several tens of micrometres, despite the low SWCNT content of 10% erties such as the high charging/discharging rate and the
which was much closer to the percolation limit than the amount long cycle stability.35–40 Charge transport through a layer of
required for the previously reported TEMPO-substituted aliphatic polymers populated with the organic robust radicals
polymethacrylate.
per repeating unit, or radical polymers, consist of an electron
self-exchange reaction between the redox-active radical sites
and the electroneutralization with counterions. Among
them, radical polyethers containing nitroxides such as
2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 2,2,5,5-
tetramethylpyrrolidin-1-oxyl enabled quantitative charging/
discharging at high current densities and long cycle life which
was most likely attributed to the nature of the main chain
analogous to PEO allowing ionic transport throughout the
polymer layer and sufficient swelling in conventional electrolyte
solutions. The PEO chain was also characterized by the excellent
chemical stability against the redox reaction, allowing charging/
discharging for more than 1000 cycles.12,41 The radical polyether
is expected to contribute to increase the thickness of the poly-
mer layer and yet to reduce the amount of carbon nanobers as
electroconductive additives while maintaining the rate perfor-
mance of the polymer/carbon composite electrode, thus giving
rise to larger charge-storage density of the composite layer
compared with other radical polymers.
However, inherent difficulties in the synthesis of radical
polyethers have deprived them of such opportunities. The
radical polyethers were originally synthesized via anionic ring-
opening polymerizations of radical monomers using potas-
sium tert-butoxide (t-BuOK) or diethylzinc/H2O catalyst. These
polymerizations resulted in either very low yields and/or decits
of radicals which primarily decreased the charging capacity of
the organic batteries.42,43
Chemistry of charge storage with electrode-active materials is
dominated by a mass-transfer process of electrolyte ions to
accomplish charge compensation throughout the electroactive
layer.1–3 The electroneutralization process is much inuenced
by diffusivity of the counterion, which has prompted many
studies on electrode-active materials designed for high ionic
conductivity, such as mesostructured lithium metalates4–11 and
polyethers bearing redox-active pendant groups.12 As typical
organic ion conductors, poly(ethylene oxide) (PEO)-based
materials have attracted much attention for their potential
application in electronic devices, such as light-emitting
diodes,13,14 thin-lm transistors,15–17 sensors,18 solar cells,19,20
and Li-ion batteries,21–24 which are expected to acquire unprec-
edented properties related to exibility, light weight, and safety.
In particular, a PEO-based electrolyte layer has been investi-
gated as a Li+ single conductor for many types of rechargeable
devices.25–27 High ionic conductivity for the electrode-active
layer is also crucial for charge compensation. Incorporation of
PEO-based materials has therefore been widely examined to
enhance the charging/discharging performance.28–32 For
example, a multifunctional block copolymer containing a PEO
segment and a conductive polymer segment was proposed as an
Department of Applied Chemistry, Waseda University, Tokyo 169-8555, Japan. E-mail:
nishide@waseda.jp; Fax: +81-3-3209-5522; Tel: +81-3-3200-2669
In this paper, we report a controlled synthesis of crosslinked
poly(4-glycidyloxy TEMPO) (CL-PTGE) with high molecular
weights and radical concentrations, and an efficient charge
† Electronic supplementary information (ESI) available: Detailed synthetic
method, electrode preparation, and electrochemical and SQUID measurements.
See DOI: 10.1039/c4ra15949g
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transport of remarkable polymer-rich CL-PTGE/carbon properties in organic electrolyte solutions. The CL-PTGE was
composite electrodes with large thicknesses up to several ten obtained with the R(OH)4/t-Bu-P4 initiator at [monomer]/
micrometers maintaining the redox capacity. Our principal [crosslinker] ¼ 100/5 in 98% yield which was increased from
nding was that alcohols with a phosphazene base44,45 was an the yield of 80% for the corresponding homopolymerization,
excellent initiator for the anionic ring-opening polymerization while the copolymerization using ROH/t-Bu-P4 resulted in only
of 4-glycidyloxy TEMPO, compared with t-BuOK which was the 77% yield. The CL-PTGE contained low composition of the
most conventional for glycidyl monomers. The present initiator redox-inactive crosslinker to minimize the loss of the charge
allowed many types of polyether architectures according to the capacity. This efficient crosslinking was attributed to the high
structure of the alcohols or polyols, which led to good disper- reactivity of the alkoxide anion activated by t-Bu-P4 and the
sion of a single-walled carbon nanotube (SWCNT) in the poly- quadruply-branched structure of R(OH)4 which also served as
mer.46,47 The CL-PTGE composite electrode demonstrated the the crosslinking point. The unpaired electron density of
fast and quantitative charging/discharging even in the thick 0.92 per monomer unit for CL-PTGE, estimated by the SQUID
layers which several ten micrometers in thickness.
magnetic measurements, revealed that the radical survived
4-Glycidyloxy TEMPO was synthesized via the Williamson during the polymerization by virtue of the low nucleophilicity of
ether synthesis from epichlorohydrin and 4-hydroxy-TEMPO. t-Bu-P4 and the moderate reaction temperature (Fig. S1†).
PTGE was prepared at room temperature via the anionic ring-
SWCNT with 1–3 nm in diameter was incorporated into a
opening polymerization of 4-glycidyloxy TEMPO using CL-PTGE layer to support long-range conduction throughout
3-phenyl-1-propanol (ROH)/tert-butyl-4,4,4-tris(dimethylamino)- the layer, with a view to maximize the overall energy density of
2,2-bis[tris(dimethylamino)phosphoranylidenamino]-2L5,4L5- the battery by reducing the amount of the conductive additive
catenadi(phosphazene) (t-Bu-P4), a strong base with low nucle- down to approach the theoretically predicted percolation limit
ophilicity, or pentaerythritol (R(OH)4)/t-Bu-P4 as a monofunc- of less than 1%.48–50 This has been an important issue in the
tional and a quadruply-branched initiator, respectively (Scheme studies of organic electrode-active materials, but has never been
1). The moderate temperature was required to suppress unde- accomplished with the conventional redox polymer/vapor-
sirable side reactions involving a deactivation of the nitroxide grown carbon nanober (VGCF) composites which always
radical moiety as observed for tꢀhe t-BuOK initiator that required required a VGCF composition of 40–60 wt%.51,52 CL-PTGE and
higher temperatures above 60 C.41 The results of the polymer- SWCNT were uniformly dispersed in CHCl3, a good solvent for
ization are summarized in Table S1.† PTGE was obtained with a both materials, using a probe sonicator and then the resultant
low polydispersity index (PDI) in ca. 70% yield using the ROH/t- mixture was cast-coated on a current collector. A SEM image of
Bu-P4 initiator at a molar ratio of 1 : 1, while the molecular the composite electrode indicated that 10 wt% SWCNT was
weight was lower than the theoretical value based on the initial homogeneously buried in a 90 wt% CL-PTGE matrix and formed
composition ratio of [monomer]/[initiator]
¼
100/1. The a network in a micrometer scale despite that SWCNT still
R(OH)4/t-Bu-P4 initiator at a molar ratio of 1 : 4 ([OH]/[t-Bu-P4] ¼ formed bundles (Fig. S2(a)†). A smaller amount of SWCNT
1/1) produced PTGE with the narrow PDI in a signicantly (5 wt%) was contrastingly buried in the 95 wt% CL-PTGE matrix
higher yield of 90%. Furthermore, the R(OH)4/t-Bu-P4 initiator without forming the network (Fig. S2(b)†). A much lower-density
at a molar ratio of 1 : 2 ([OH]/[t-Bu-P4] ¼ 2/1) gave PTGE in 80% network was formed with 10 wt% VGCF with a larger diameter
yield, in contrast to the R(OH)/t-Bu-P4 initiator at the same of 150 nm than that of SWCNT (Fig. S2(c)†). The higher dis-
molar ratio of [OH]/[t-Bu-P4] which produced only a trace persivity of SWCNT obviously suggested the affinity with PTGE,
amount of the polymer in 4% yield. Copolymerization of 4-gly- which was reminiscent of the molecular wrapping of SWCNT
cidyloxy TEMPO and 1,4-butanediol diglycidyl ether as a cross- with a TEMPO-substituted polymethacrylate in our previous
linker was carried out to yield the CL-PTGE with a sufficient study.47 The conductivity of the 10 wt% SWCNT composite
crosslinking density to realize the swelling but insoluble (42 mS cmꢁ1), measured by the four-probe method with 1 mm
regular probe intervals, was higher than those of the 5 wt%
SWCNT composite (14 mS cmꢁ1) and the 10 wt% VGCF
composite (2.3 mS cmꢁ1) (Table S2†), suggesting that the
10 wt% SWCNT was sufficient to form the conductive path
throughout the composite electrode at the macroscopic scale.
Electrochemical properties of the three composite electrodes
with ca. 10 mm in thickness were examined in a typical three-
electrode cell using a Pt coil and an Ag/AgCl as the counter and
the reference electrodes, respectively. Cyclic voltammograms
obtained with the composite electrodes all displayed a reversible
redox wave at 0.73 V (vs. Ag/AgCl) in a 0.1 M (n-C4H9)4NClO4/
acetonitrile electrolyte solution (Fig. 1 and S3†).
The redox cyclability of the electrodes indicated that
CL-PTGE strongly adhered to the electrode substrate and hence
served also as a binder. The 10 wt% SWCNT composite elec-
trode displayed a narrow peak-to-peak separation and a large
Scheme 1 Anionic ring-opening copolymerization of 4-glycidyloxy
TEMPO and 1,4-butanediol diglycidyl ether.
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Fig. 1 (a) Cyclic voltammograms obtained for the CL-PTGE elec-
trodes containing 0 or 10 wt% SWCNT at a scan rate of 5 mV sꢁ1. The
electrolyte was a solution of 0.1 M (n-C4H9)4NClO4 in CH3CN.
(b) Schematic representation for charge transportation in the
CL-PTGE/SWCNT composite layer swelling the electrolyte solution.
Fig. 3 Charging/discharging curves for a coin-type cell consisted of
the CL-PTGE/10 wt% SWCNT composite cathode and the lithium
anode with 1.0 M LiPF6 in ethylene carbonate/diethyl carbonate (1/1 in
v/v) at 1–10 C rates. Inset: cycle performance of the cell.
charging capacity in comparison with the 0 and 5 wt% SWCNT
and the 10 wt% VGCF composites. Coulometric titration
experiments by chronopotentiometry also revealed the highest
charging/discharging capacity for the 10 wt% SWCNT
composite electrode (Fig. S4†).
wt% SWCNT composite electrode (41 U cmꢁ2) was comparable
to that of the non-composite electrode of CL-PTGE (44 U cmꢁ2),
while other composite electrodes exhibited higher resistances
(Table S2†). Transition from the diffusion controlled region
(with a slope of 45ꢀ to the x axis) to the charge saturation region
(90ꢀ) in the impedance spectrum for the 10 wt% SWCNT
composite electrode indicated that the nite diffusion was
realized at low frequencies, while the non-composite CL-PTGE
exhibited a semi-innite diffusional behavior even at very low
frequency regions (Fig. S5†). This difference was most likely
ascribed to the shortened diffusion length for the electro-
neutralizing ions in the composite layer due to the long-range
charge transport supported by the SWCNT network
throughout the composite layer.
We fabricated a test full-cell consisted of a 10 wt% SWCNT
composite cathode, a lithium anode, a separator lm, and a
1.0 M LiPF6 in ethylene carbonate/diethyl carbonate electrolyte
solution. The charging/discharging curve at 1 C rate displayed a
plateau voltage at 3.5 V corresponding to the potential differ-
ence between the cathode and the anode (Fig. 3).‡ The charge
capacity was 80 mA h gꢁ1 (80% of the theoretical capacity) and
maintained over 70% of the initial capacity aer 200 cycles. The
excellent rate performance for the charging/discharging process
of the CL-PTGE composite electrode gave rise to a high rate
capability of the cell, allowing fast charging and discharging in
10 C without loss of the charge-storage capacity. Whilst some
inorganic electrode-active materials in lithium ion batteries
have been recently achieving the fast charging/discharging
capabilities (>100 C),53,54 organic electrode-active materials
still have advantages in terms of tuning the chemical structures
for faster ion mobilities and quick redox reactions allowing the
ultrafast charging/discharging ability (>2000 C).55 Fabricating
the high-performance, exible, and lightweight all-organic
batteries56 will also be our next challenge.
The excellent charge storage properties of the 10 wt%
SWCNT composite electrode originated from the higher
conductivity of the layer. The charging/discharging properties
of the 5 wt% and the 10 wt% SWCNT composite electrodes and
the non-composite (or pristine polymer-coated) electrode with
ca. 40 mm in thickness were examined (Fig. 2(a)). The 10 wt%
SWCNT markedly increased the discharging capacity of the
composite electrode up to 93 mA gꢁ1 that corresponded to 90%
of the theoretical or formula weight-based capacity from
20 mA h gꢁ1 (20%) for the non-composite electrode, while the
charging capacity of the 5 wt% SWCNT composite electrode was
limited to 69 mA h gꢁ1. The difference in plateau potentials for
discharging between 0.62 V for the 10 wt% SWCNT composite
electrode and 0.54 V for the non-composite electrode demon-
strated the less resistive properties established with SWCNT.
The 10 wt% SWCNT composite electrode displayed a high
current density, even at a 30 C rate, with a quantitative charging/
discharging capacity (Fig. 2(b)).‡ The resistance of the
composite electrodes were also estimated from AC impedance
measurements. The total charge-transfer resistance for the 10
Conclusions
Fig. 2 Charging/discharging performance of the CL-PTGE electrodes
(a) containing 0, 5, and 10 wt% SWCNT at 10 C rate, and (b) containing
10 wt% SWCNT at 10–30 C rate. The electrolyte was a solution of 0.1 M
(n-C4H9)4NClO4 in CH3CN.
CL-PTGE was successfully synthesized via anionic ring-opening
copolymerization of the 4-glycidyloxy TEMPO and a small
amount of the diglycidyl ether as
a crosslinker using
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pentaerythritol/t-Bu-P4
initiator.
The
CL-PTGE/SWCNT 18 M. Yuasa and K. Oyaizu, Curr. Org. Chem., 2005, 9, 1685–
composite electrode (9/1 in w/w) exhibited a quantitative
charging/discharging at high current densities with a long cycle 19 J. E. Benedetti, M. A. de Paoli and A. F. Nogueira, Chem.
life, due to the low resistance supported by the conductive Commun., 2008, 1121–1123.
network of SWCNT and the high affinity of CL-PTGE to the 20 F. S. Freitas, J. N. de Freitas, B. I. Ito, M.-A. De Paoli and
1697.
electrolyte solution. The combination of the crosslinked poly-
(glycidyl ether) and SWCNT showed great potential in utilizing
redox polymers for energy devices.
A. F. Nogueira, ACS Appl. Mater. Interfaces, 2009, 1, 2870–
2877.
21 K. P. Barteau, M. Wolffs, N. A. Lynd, G. H. Fredrickson,
E. J. Kramer and C. J. Hawker, Macromolecules, 2013, 46,
8988–8994.
22 a. Blazejczyk, W. Wieczorek, R. Kovarsky, D. Golodnitsky,
E. Peled, L. G. Scanlon, G. B. Appetecchi and B. Scrosati, J.
Electrochem. Soc., 2004, 151, A1762.
23 R. Bouchet, S. Maria, R. Meziane, A. Aboulaich, L. Lienafa,
J. Bonnet, T. N. T. Phan, D. Bertin, D. Gigmes, D. Devaux,
R. Denoyel and M. Armand, Nat. Mater., 2013, 12, 452–457.
24 F. Croce, G. B. Appetecchi, L. Persi and B. Scrosati, Nature,
1998, 394, 456–458.
Acknowledgements
This work was partially supported by Grants-in-Aid for Scientic
Research (no. 24108739, 24225003, 25107733, and 25288056)
and the Leading Graduate Program in Science and Engineering,
Waseda University from MEXT, Japan. Support by the project
“Functional Redox Polymers” of Waseda Advanced Research
Institute for Science & Engineering is acknowledged.
25 K. Sinha and J. K. Maranas, Macromolecules, 2011, 44, 5381–
5391.
Notes and references
26 K. Sinha, W. Wang, K. I. Winey and J. K. Maranas,
Macromolecules, 2012, 45, 4354–4362.
‡ The 1 C rate is dened as the current density at which the charging or dis-
charging of the cell takes 1 h.
´
¨
27 P. Novak, K. Muller, K. S. V. Santhanam and O. Haas, Chem.
1 H. Nishide and K. Oyaizu, Science, 2008, 319, 737–738.
Rev., 1997, 97, 207–282.
2 K. Oyaizu and H. Nishide, Adv. Mater., 2009, 21, 2339–2344. 28 Z. Jia, W. Yuan, H. Zhao, H. Hu and G. L. Baker, RSC Adv.,
3 W. Choi, D. Harada, K. Oyaizu and H. Nishide, J. Am. Chem.
Soc., 2011, 133, 19839–19843.
2014, 4, 41087–41098.
29 H. Hu, W. Yuan, L. Lu, H. Zhao, Z. Jia and G. L. Baker, J.
4 P. L. Taberna, S. Mitra, P. Poizot, P. Simon and
J.-M. Tarascon, Nat. Mater., 2006, 5, 567–573.
Polym. Sci., Part A: Polym. Chem., 2014, 52, 2104–2110.
30 H. Hu, W. Yuan, Z. Jia and G. L. Baker, RSC Adv., 2014, 5,
5 A. Manthiram and J. Kim, Chem. Mater., 1998, 10, 2895–2909.
3135–3140.
¨
¨
6 M. Wilkening, C. Muhle, M. Jansen and P. Heitjans, J. Phys. 31 M. J. Lacey, F. Jeschull, K. Edstrom and D. Brandell, Chem.
Chem. B, 2007, 111, 8691–8694.
7 G. Yang, G. Wang and W. Hou, J. Phys. Chem. B, 2005, 109, 32 J. Xiao, X. Wang, X.-Q. Yang, S. Xun, G. Liu, P. K. Koech, J. Liu
11186–11196.
and J. P. Lemmon, Adv. Funct. Mater., 2011, 21, 2840–2846.
8 P. Zhang, Y. Wu, D. Zhang, Q. Xu, J. Liu, X. Ren, Z. Luo, 33 A. E. Javier, S. N. Patel, D. T. Hallinan, V. Srinivasan and
Commun., 2013, 49, 8531–8533.
M. Wang and W. Hong, J. Phys. Chem. A, 2008, 112, 5406–
N. P. Balsara, Angew. Chem., Int. Ed. Engl., 2011, 50, 9848–
5410.
9851.
`
9 A. S. Arico, P. Bruce, B. Scrosati, J. Tarascon and W. van 34 S. N. Patel, A. E. Javier and N. P. Balsara, ACS Nano, 2013, 7,
Schalkwijk, Nat. Mater., 2005, 4, 366–377. 6056–6068.
10 S. Myung, S. Komaba, K. Hosoya, N. Hirosaki, Y. Miura and 35 T. Suga, S. Sugita, H. Ohshiro, K. Oyaizu and H. Nishide, Adv.
N. Kumagai, Chem. Mater., 2005, 17, 2427–2435. Mater., 2011, 23, 751–754.
11 K. T. Nam, D. Kim, P. J. Yoo, C.-Y. Chiang, N. Meethong, 36 T. Janoschka, M. D. Hager and U. S. Schubert, Adv. Mater.,
P. T. Hammond, Y. Chiang and A. M. Belcher, Science,
2006, 312, 885–888.
12 K. Oyaizu, T. Kawamoto, T. Suga and H. Nishide,
Macromolecules, 2010, 43, 10382–10389.
2012, 24, 6397–6409.
37 I. S. Chae, M. Koyano, T. Sukegawa, K. Oyaizu and
H. Nishide, J. Mater. Chem. A, 2013, 1, 9608.
38 T. Sukegawa, A. Kai, K. Oyaizu and H. Nishide,
Macromolecules, 2013, 46, 1361–1367.
13 S. van Reenen, P. Matyba, A. Dzwilewski, R. A. J. Janssen,
L. Edman and M. Kemerink, J. Am. Chem. Soc., 2010, 132, 39 L. Bugnon, C. J. H. Morton, P. Novak, J. Vetter and
13776–13781. P. Nesvadba, Chem. Mater., 2007, 19, 2910–2914.
14 T. Wagberg, P. R. Hania, N. D. Robinson, J.-H. Shin, 40 T. Hyakutake, J. Y. Park, Y. Yonekuta, K. Oyaizu, H. Nishide
P. Matyba and L. Edman, Adv. Mater., 2008, 20, 1744–1749.
and R. Advincula, J. Mater. Chem., 2010, 20, 9616.
15 J. Lee, M. J. Panzer, Y. He, T. P. Lodge and C. D. Frisbie, J. Am. 41 T. Suga, K. Yoshimura and H. Nishide, Macromol. Symp.,
Chem. Soc., 2007, 129, 4532–4533.
2006, 245–246, 416–422.
16 K. H. Lee, S. Zhang, Y. Gu, T. P. Lodge and C. D. Frisbie, ACS 42 T. Endo, K. Takuma, T. Takata and C. Hirose,
Appl. Mater. Interfaces, 2013, 5, 9522–9527. Macromolecules, 1993, 26, 3227–3229.
17 J. Liu, I. Engquist, X. Crispin and M. Berggren, J. Am. Chem. 43 K. Oyaizu, T. Suga, K. Yoshimura and H. Nishide,
˚
Soc., 2012, 134, 901–904.
Macromolecules, 2008, 41, 6646–6652.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 15448–15452 | 15451

View Article Online
RSC Advances
Communication
44 T. Isono, K. Kamoshida, Y. Satoh, T. Takaoka, S. Sato, 50 J. C. Grunlan, a. R. Mehrabi, M. V. Bannon and J. L. Bahr,
T. Satoh and T. Kakuchi, Macromolecules, 2013, 46, 3841–
3849.
45 H. Misaka, E. Tamura, K. Makiguchi, K. Kamoshida,
Adv. Mater., 2004, 16, 150–153.
51 S. Yoshihara, H. Katsuta, H. Isozumi, M. Kasai, K. Oyaizu
and H. Nishide, J. Power Sources, 2011, 196, 7806–7811.
R. Sakai, T. Satoh and T. Kakuchi, J. Polym. Sci., Part A: 52 S. Yoshihara, H. Isozumi, M. Kasai, H. Yonehara, Y. Ando,
Polym. Chem., 2012, 50, 1941–1952.
46 W. Choi, S. Endo, K. Oyaizu, H. Nishide and K. E. Geckeler, J.
Mater. Chem. A, 2013, 1, 2999.
K. Oyaizu and H. Nishide, J. Phys. Chem. B, 2010, 114,
8335–8340.
53 B. Kang and G. Ceder, Nature, 2009, 458, 190–193.
47 W. Choi, S. Ohtani, K. Oyaizu, H. Nishide and K. E. Geckeler, 54 W. Tang, S. Tian, L. L. Liu, L. Li, H. P. Zhang, Y. B. Yue,
Adv. Mater., 2011, 23, 4440–4443.
48 A. V. Kyrylyuk and P. van der Schoot, Proc. Natl. Acad. Sci. U.
S. A., 2008, 105, 8221–8226.
49 J.-M. Benoit, B. Corraze, S. Lefrant, W. J. Blau, P. Bernier and
O. Chauvet, Synth. Met., 2001, 121, 1215–1216.
Y. Bai, Y. P. Wu and K. Zhu, Electrochem. Commun., 2011,
13, 205–208.
55 K. Koshika, N. Sano, K. Oyaizu and H. Nishide, Chem.
Commun., 2009, 836–838.
56 T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu and H. Nishide, Adv.
Mater., 2009, 21, 1627–1630.
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