Supplementary Information

Aromatic Porous-honeycomb Electrodes for Sodium-organic Energy Storage Devices

Ken Sakaushi1,2,3*, Eiji Hosono3, Georg Nickerl2, Thomas Gemming1, Haoshen Zhou3,

Stefan Kaskel2 & Jürgen Eckert1,4

1IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, D-01069 Dresden, Germany.

2TU Dresden, Department of Inorganic Chemistry, Bergstr. 66, D-01069 Dresden, Germany.

3National Institute of Advanced Industrial Science and Technology, Energy Technology Research

Institute, 1-1-1 Umezono, Tsukuba 305-8568, Japan.

4TU Dresden, Institute of Materials Science, Helmholtzstr. 7, D-01069 Dresden, Germany.

*e-mail: k.sakaushi@ifw-dresden.de

120013001400150016001700180019002000

Wave number (cm-1)

Tra

nce

mitta

nce (

a.u

.)

12

Supplementary Figure S1 | Fourier transform infrared (FT-IR) for the bipolar porous organic

electrode (BPOE). The peak 1 is originated from triazine rings and the peak 2 is originated from

open-chain imino29.

2 Theta (degree)

5 10 15 20 25 30 35 40 45 50

Inte

nsity

(a.

u.)

Supplementary Figure S2 | X-ray diffraction measurement for the bipolar porous organic

electrode.

Po

tential (V

vs. N

a/N

a+)

0 50 100 150 200 250

Specific capacity (mAh g−1)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Supplementary Figure S3 | OCV curve (discharge) for the sodium-organic energy storage

device. A current density of 30 mA g-1 was applied 10 minutes for BPOE and 30 minutes of a

relaxation time was taken to achieve a quasi-equilibrium state. This cycle was continued until

reaching of the potential of BPOE to 1.3 V vs. Na/Na+.

1000 1200 1400 1600 1800

Raman shift (cm-1)

inte

nsity

(a.

u.)

G peak

Supplementary Figure S4 | Raman spectrum of the BPOE after 7,400 cycles. The existence of G

peak even after 7,400 charge-discharge cycling reveals the high stability of the 2D framework of the

BPOE.

Supplementary Figure S5 | Picture of the sodium-organic energy storage device after 1,000

cycles using 1M NaClO4 in EC:DEC as an electrolyte. Initial (left) and after over 1,000 cycles

(right).

0

1

2

3

4

0 50 100 150 200 250

0

1

2

3

4

0 20 40 60 80 100 120

0

1

2

3

4

0 20 40 60 80 100

Pote

ntial (V

vs.

Na/N

a+)

Pote

ntial (V

vs.

Na/N

a+)

Pote

ntia

l (V

vs.

Na/N

a+)

0

1

2

3

0 10 20 30 40 50

Specific capacity (mAh g−1) Specific capacity (mAh g−1)

Specific capacity (mAh g−1)Specific capacity (mAh g−1)

0

1

2

3

0 2 4 6 8 10

Po

tentia

l (V

vs.

Na

/Na

+)

Pote

ntia

l (V

vs.

Na/N

a+)

Specific capacity (mAh g−1)

E = 502 Wh kg−1 E = 285 Wh kg−1

E = 204 Wh kg−1 E = 82 Wh kg−1

E = 14 Wh kg−1

Current density = 0.01 A g −1 Current density = 0.1 A g −1

Current density = 1 A g −1 Current density = 5 A g −1

Current density = 10 A g −1

a b

c d

e

Supplementary Figure S6 | Discharge curves for the calculation of specific energy and power in

Fig. 6a. a, Typical discharge curve at a current density of 0.01 A g−1. b, Typical discharge curve at a

current density of 0.1 A g−1. c, Typical discharge curve at a current density of 1 A g−1. d, Typical

discharge curve at a current density of 5 A g−1. e, Typical discharge curve at a current density of 10

A g−1.

0

1

2

3

4

0 10 20 30 40 50

0

1

2

3

4

0 20 40 60 80 100

0

1

2

3

4

0 20 40 60 80 100 1200

1

2

3

4

0 50 100 150 200 250

Pote

ntia

l (V

vs.

Na

/Na

+)

Pote

ntia

l (V

vs.

Na

/Na

+)

Po

ten

tial (V

vs.

Na/N

a+)

Specific capacity (mAh g−1) Specific capacity (mAh g−1)

Specific capacity (mAh g−1)Specific capacity (mAh g−1)

Pote

ntia

l (V

vs.

Na

/Na

+)

E = 658 Wh kg−1 E = 339 Wh kg−1

E = 258 Wh kg−1 E = 147 Wh kg−1

0.01 A g −1 0.1 A g −1

1 A g −1 5 A g −1

a b

c d

Supplementary Figure S7 | Charge curves for the calculation of the round-trip energy

efficiency in Fig. 6b. a, Typical charge curve at a current density of 0.01 A g−1. b, Typical charge

curve at a current density of 0.1 A g−1. c, Typical charge curve at a current density of 1 A g−1. d,

Typical charge curve at a current density of 5 A g−1. Here, we can calculate the energy efficiency of

the sodium-organic energy storage device by combing Figure S6. For example, the energy efficiency

at a current density of 1 A g−1 is: 502 Wh kg−1 / 658 Wh kg−1 × 100 = 76 %.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 7 14

Time (day)

Pote

ntial (

V v

s.

Na/N

a+)

83 % 78 %

Supplementary Figure S8 | Self-discharge property of the BPOE. The BPOE maintained 83 % of

the charged potential up to 4.1 V vs. Na/Na+ after 7 days. Even after 14 days, the BPOE maintained

78 % of the charged potential.

C1

R2

-Z’’

(Ω)

Z’ (Ω)

:measured

:Fitting

100,000 200,000 300,000

100,000

50,000

150,000

200,000

Process 1 Process 2 Process 3

0

0

Supplementary Figure S9 | Nyquist plot for the as-prepared BPOE. We observed three circles:

resistance for the BPOE indicating Process 1, at the grain boundary of the BPOE indicating Process

2, and of BPOE/electrode interface indicating Process 3, from highest frequency respectively. The

inset equivalent circuit was used for the fitting of the first semi-circle. A frequency range from 10

mHz to 10 kHz with an amplitude of 500 mV was applied for the impedance spectroscopy

measurement. Each point at a frequency was taken ten times and showed their average value. We

used the steel electrodes to hold the pellet of the BPOE and to measure the impedance spectroscopy

technique at 25 ˚C.

Supplementary Table S1 | Comparison of the rate capability for the p-undoping and n-doping

processes

Current density

0.01 A g−1

Current density

0.1 A g−1

Current density

1.0 A g−1

p-undoping (mAh g–1) 55 50 35

p-undoping (Normalized by the

specific capacity at 0.01 A g−1) 100 % 91 % 64 %

n-doping (mAh g–1) 185 70 60

n-doping (Normalized by the

specific capacity at 0.01 A g−1) 100 % 38 % 32 %

Supplementary Discussion | Conductivity of the as-prepared BPOE.

By using impedance spectroscopy, one can measure the resistance of materials. In case of an

aggregate of particles, one can investigate the resistances of the particles, at the grain boundary, and

at a particles/electrode interface, respectively61. We are interested in the resistance of the material,

therefore, we focus on the resistance of the particles. The response for the resistance of the material

comes at the highest frequency region.

We used steel electrodes and held a pellet of the as-prepared BPOE by using them to

measure the impedance spectroscopy response. Supplementary Figure S9 shows the Nyquist plot of

the BPOE. We observed three semi-circles and the circle at the highest frequency region indicates the

response related to the resistance of the BPOE. We confirmed that the resistance of the BPOE is

105,232 Ω by fitting.

Conductivity σ (S cm−1) is given by the following equation where l is the thickness of the

pellet (= 0.43 cm), S is the area of the pellet (= 1 cm2), and Ω is the resistance of the BPOE

σ = l/S × 1/Ω

Therefore, the conductivity of the BPOE is 4.09×10−6 S cm−1 at 25 ˚C.

Supplementary Reference

61. Tanase, S. On the electronic conductivity measurements. Electrochemistry 71, 814–819 (2003).