1

Supplementary Material

Morphology control of lithium peroxide using Pd3Co as an additive in

aprotic Li-O2 batteries

Sung Man Cho, Jee Ho Yom, Sun Woo Hwang, Il Won Seong, Jiwoong Kim, Sung Ho Cho,

Woo Young Yoon*

Department of Materials Science and Engineering, Korea University, 1, 5Ga, Anam-dong,

Sungbuk-Gu, Seoul 136-701, Republic of Korea.

*Corresponding author:

E-mail address: wyyoon@korea.ac.kr (W.Y. Yoon)

Tel.: +82 2 3290 3274; Fax: +82 2 928 3584

1

2

Figure S1. TGA results of Pd3Co/KB powder.

The TGA result shows that the total weight loss of Pd3Co/KB powder is 43.04% up to 800 C, which corresponds to its carbon content. The slight weight increase starting at ~300 °C is caused by oxidation of the sample. This result is attributed to TGA being carried out under an air atmosphere [1-3].

2

3

Figure S2. High-resolution SEM images of (a) KB and (b) Pd3Co/KB cathodes after full discharge at 25 µA cm-2.

3

4

4

5

Figure S3. SEM images of KB (top) and Pd3Co/KB (bottom) cathodes at different discharge

states (0, 10, 20, 40 h, and fully discharged).

Figure S4. The discharge curves of (a) KB and (b) Pd3Co/KB cathodes at various current densities (10, 25, 50, 100, 250, and 500 µA cm-2). (c) A plot of discharge capacity versus

current density.

5

6

As shown in the discharge curves of Fig. S4(a and b), for a higher applied current density, the discharge capacity generally decreases and has a lower plateau voltage. However, abrupt changes in the voltage plateau and the discharge capacity were observed between 50 and 100 µA cm-2. Figure S4(c) shows the capacity of KB and Pd3Co/KB cathodes at various current densities. The sudden capacity drop for current density over the range 50–100 µA cm -2

indicates that the dominant reaction pathway changes from a solution-mediated process to a surface-mediated process [4]. To obtain high capacity, toroidal Li2O2 growth should occur through the solution-mediated process. High carbon loading on the same electrode surface area may enable solution-mediated growth at considerably higher current density because of the highly active surface area [5].

6

7

References

[1] S.Yan, H. Maeda, K. Kusakabe, S. Morooka, Thin palladium membrane formed in support pores by metal-organic chemical vapor deposition method and application to hydrogen separation, Ind. Eng. Chem. Res. 33 (1994) 616-622.

[2] M.-C. Chiu, W.-P. Hsieh, W.-Y. Ho, D.-Y. Wang, F.-S. Shieu, Thermal stability of Cr-doped diamond-like carbon films synthesized by cathodic arc evaporation, Thin Solid Films 476 (2005) 258-263.

[3] P. Song, D. Wen, Z. X. Cuo, T. Korakianitis, Oxidation investigation of nickel nanoparticles, Phys. Chem. Chem. Phys. 10 (2008) 5057-5065.

[4] B.D. Adams, C. Radtke, R. Black, M.L. Trudeau, K. Zaghib, L. F. Nazar, Current density dependence of peroxide formation in the Li-O2 battery and its effect on charge, Energy Environ. Sci. 6 (2013) 1772–1778.

[5] S. Meini, M. Piana, H. Beyer, J. Schwämmlein, H.A. Gasteiger, Effect of carbon surface area on first discharge capacity of Li-O2 cathodes and cycle-life behavior in ether-based electrolytes, J. Electrochem. Soc. 159 (2012) A2135–A2142.

7