Supporting Information

Transcription

1 upporting Information Dendrite-Free Polygonal odium Deposition with Excellent Interfacial tability in a NaAlCl Inorganic Electrolyte Juhye ong, Goojin Jeong,*, Ah-Jung Lee, Jong Hwan Park, Hansu Kim,*, and Young-Jun Kim Department of Energy Engineering, Hanyang University, eoul , Korea Advanced Batteries Research Center, Korea Electronics Technology Institute, eongnam , Korea Corresponding author: gjeong@keti.re.kr; khansu@hanyang.ac.kr -1

2 Figure 1. A EM image of fresh Na-metal surface before contacting any electrolytes. -2

3 C 1s Al 2p Binding energy (ev) Binding energy (ev) Figure 2. C 1s (left) and Al 2p (right) XP spectra of Na-metal surface after contacting NaAlCl inorganic electrolyte. -3

4 Na 1s (1072.5) 1s C 1s NaH (1072.8) Na 2 Na 2 C 3 (1071.5) NaH (532.8) Na 2 C 3 (531.6) Na 2 (529.7) Hydrocarbon (285) Carbonate (~289) Etching time increases (1 min interval) Binding Energy (ev) Binding Energy (ev) Binding Energy (ev) Figure 3. XP spectra of the native film of Na metal before contacting any electrolytes -4

5 C 1s Binding energy (ev) Figure 4. C 1s XP spectra of Na-metal surface after contacting 1 M NaPF 6 EC:PC organic electrolyte. -5

6 Figure 5. The EM images of the Na electrodeposit on Ni substrate in NaAlCl4-22 electrolyte. The morphology of Na deposit on Ni substrate is as same as observed on the Na electrode (Figure 4a and b): a dendrite-free polygonal structure exhibiting the cuboidal crystallographic nature of the Na metal. The current density for Na deposition was 0.5 ma cm 2. (a) The deposited amount of 2.5 ma h cm 2, (b) The deposited amount of 5 ma h cm 2-6

7 Figure 6. The EM-ED results of Na electrodeposit on Ni substrate in NaAlCl electrolyte. (a) EM image and (b) Na, (c) Cl, (d), and (e) Ni elemental ED mapping. (f) Quantitative element analysis table. -7

8 Calculation for averaged Coulombic efficiency of Na metal electrode using a Na/Na symmetric cell First of all, the figure-of-merit (FM) for averaged Coulombic efficiency of Na metal electrode was determined by Eq. (1). FM = accumulated discharge capacity to the end of cycle Na capacity in a cell = n A B (1),where n is the total cycle number before the stripping voltage reaches 1.0 V; A the reversible capacity during cycling; B the initial loading capacity of working Na electrode in a cell. For the cell of NaAlCl inorganic electrolyte shown in Fig. 1c (top), n is 95, A is 1.5 mah cm 2, and B is 17.5 mah cm 2, which results into FM of Then, the averaged Coulombic efficiency (Eff) was calculated from the FM by Eq. (2). Eff = (2) FM Therefore, the averaged Coulombic efficiency of the Na metal electrode in the NaAlCl inorganic electrolyte is about 88%. More information about this method can be found in the literature. 1-8

9 Possible reaction schemes on Na electrode in NaAlCl inorganic electrolyte. According to the literature, 2 the following reactions on the Na electrode in NaAlCl inorganic electrolyte may be suggested; 6Na + 2 2Na 2 + Na 2 Na Na Na (1) (2) Na Na Na (3) 2Na Na Na (4) The formation of Na 2 n 6 may occur through the following sequence of reactions starting with Na Na + Na Na 2Na 2 + Na Na (I) (5) Na Na Na Na (6) (II) Na-reduction 2 reduction II Na 2 n 6, n > 4 (7) -9

10 REFERENCE (1) aito, K.; Nemoto, Y.; Tobishima,.; Yamaki, J. Improvement in Lithium Cycling Efficiency by Using Additives in Lithium Metal. J. Power ources 1997, 68, (2) Abraham, K. M.; Chaudhri,. M. The Lithium urface Film in the Li/ 2 Cell. J. Electrochem. oc. 1986, 133,