Supporting Information

Mechanically Reinforced–CNT Cathode for Li–O2 Battery with Enhanced Specific Energy via Ex Situ Pore Formation

Alan Christian Lim† a, Hyuk Jae Kwon † b, Heung Chan Leeb, Dong Joon Leeb, Hyunpyo Leeb, Hyun Jin Kimb, Dongmin Imb,*, Jeong Gil Seo* a,

Estimation of Specific Energy of Li–O2 Battery

The specific energies of the Li–O2 cells were estimated using the data listed in Table S1 and

with reference to Refs. [S1]–[S3]. For the anode, the amount of Li metal was estimated to be

3 times the number of moles of electrons employed for full capacity. The weights of the GDL

and interlayer for the Li metal (PEO in Celgard film) with a separator were 0.7 mg/cm2 and

2.8 mg/cm2, respectively. The cathode weights were experimentally measured and are listed

in Table S1. To obtain the values in Table S2, 1 mg/cm2 of CNT (65.8% based on polymer

weight) was applied instead of the actual CNT weight in this study (0.95 mg/cm2) for

calculational convenience, and the CNT nanofiber weight was then determined to be 2.52

mg/cm2. The amount of electrolyte was increased from 1 mg/cm2 to 6 mg/cm2 to confirm the

effect of the electrolyte weight on the cell specific energy. For the cell specific energy

calculations, the nominal voltage was 2.6 V. In Table S1, the capacity with 65.8% CNTs

loaded into the nanofiber cathode was experimentally measured during the discharge process.

The capacities in Table S2 were calculated based on the measured capacity of the nanofiber

cathode. The exact calculation methods are specified in the “Calculation” column in Table

S1.

Table S1. Calculation of specific energy for the nanofiber cathode (65.8% CNT).

# Parameter Unit Value Calculation(1) Molecular weight of Li g/mol 6.941(2) GDL_mass/area (S1) mg/cm2 0.7(3) Li_mass/area (S2,3) mg/cm2 3.54 (10)*3*(1)*1000/26800(4) Interlayer_mass/area (S1) mg/cm2 2.8(5) Cathode_mass/area mg/cm2 7.485 (6) + (7)(6) Electrolyte_mass/area mg/cm2 5.092(7) Nanofiber_mass/area mg/cm2 2.393(8) CNT_mass/area mg/cm2 0.950 (7)*0.397(9) Total cell_mass/area mg/cm2 14.52 sum ((2) : (5))(10) Nominal voltage V 2.6(11) Capacity mAh 4.55(12) Energy mWh 11.83 (10)*(11)(13) Specific capacity_cell mAh/g-cell 313.4 (11)/(9)*1000(14) Specific capacity_cathode mAh/g-cathode 607.9 (11)/(5)*1000(15) Specific capacity_CNT mAh/g-CNT 4789.5 (11)/(8)*1000(16) Specific energy Wh/kg 814 (12)/(9)*1000

IL/CNT = 5.36 is the reference point

Table S2. Calculation of specific energy for various IL/CNT weight ratios (blue line of Figure 5).

Parameter Unit IL/CNT1 2 3 4 5 6

GDL_mass/area mg/cm2 0.7 0.7 0.7 0.7 0.7 0.7Li_mass/area mg/cm2 3.73 3.73 3.73 3.73 3.73 3.73

Interlayer_ mass/area mg/cm2 2.8 2.8 2.8 2.8 2.8 2.8Nanofiber_mass/area mg/cm2 2.52 2.52 2.52 2.52 2.52 2.52

CNT_mass/area mg/cm2 1.0 1.0 1.0 1.0 1.0 1.0Electrolyte_mass/area mg/cm2 1.0 2.0 3.0 4.0 5.0 6.0

Cathode_mass/area mg/cm2 3.52 4.52 6.52 7.52 8.52 9.52Total cell_mass/area mg/cm2 10.75 11.75 12.75 13.75 14.75 15.75

Nominal voltage V 2.6 2.6 2.6 2.6 2.6 2.6Capacity mAh 4.8 4.8 4.8 4.8 4.8 4.8Energy mWh 12.48 12.48 12.48 12.48 12.48 12.48

Specific capacity_cell mAh/g-cell 446.5 408.5 376.5 349.1 325.4 304.8Specific capacity_cathode mAh/g-cathode 1364 1062 870 736 638 563

Specific capacity_CNT mAh/g-CNT 4800 4800 4800 4800 4800 4800

Specific energy Wh/kg 1161 1062 979 908 846 792

Figure S1. Schematic illustration of the customized hybrid cell structure.

Figure S2. (a) N2 adsorption–desorption isotherm. (b) Pore size distribution of CNTs

(Barrett-Joyner-Halenda method).

Figure S3. Capacity profiles of Li-O2 cells with various composite CNT–polymer nanofibers

comprising CNT (5–50 wt.%)–PAN; air conditions: 1 atm O2, operating temperature: 80 oC,

current density: 0.24 mA/cm2, nanofiber: 2–3 mg, IL/CNT: 4–36 (wt/wt).

0

5

10

15

20

0 20 40 60 80 100 120 140 160 180

Ele

ctro

lyte

upt

ake

(%)

Soaking Time (min)

PMMAPAN

0

10

20

30

40

0 20 40 60 80 100 120 140

Ele

ctro

lyte

upt

ake

(%)

Temperature (oC)

PAN

a b@ RT

Figure S4. Rate of electrolyte uptake into the PAN and PMMA polymer films with respect to

(a) time at RT and (b) temperature for 180 mins.

,

where W0 is the polymer film weight before electrolyte soaking and W1 is the polymer film

weight after electrolyte soaking.

BA

5 μm 5 μm

Figure S5. SEM images of nanofibers after hot pressing for 2 hrs at 120 °C

Figure S6. (a) N2 adsorption–desorption isotherm. (b) Pore size distribution of CNT-PAN-

PVP before and after hot press (Barrett-Joyner-Halenda method).

Figure S7. Electronic conductivity according to DC measurements performed on CNT–

polymer composite nanofiber with IL at 80 °C for 10 h (I–V curve) at (a) 50% CNT and (b)

20% CNT. (c) Specific capacities of composite nanofibers (50% and 20% CNT); g-cathode:

weight including CNT, polymers, and electrolyte, area: 0.5 cm2, comparison with current

density of 0.24 mA/cm2.

References

S1 H. C. Lee, J. O. Park, M. Kim, H. J. Kwon, J. -H. Kim, K. H. Choi, K. Kim, K., D. Im,

Joule 3 (2019) 542-556.

S2 J. Christensen, P. Albertus, P., Sanchez-Carrera, R. S. T. Lohmann, B. Kozinsky, R.

Liedtke, J. Ahmed, A. Kojic, J. Electrochem. Soc. 159 (2012) R1–R30.

S3 W. Choi, M. Kim, J. O. Park, J.-H. Kim, K. Choi, Y. S. Kim, T. Y. Kim, K. Ogata, D. Im,

S.-G. Doo, Y. Hwang, Sci. Rep. 7 (2017) 1-9.