# Electochemically Engineered Mesoporous Sn-Oxide Rods for Anode Materials in Lithium-Ion Batteries
## 3 Results and Discussion  
### Sn Rod Formation Using Electrodeposition  
Figure 1a-f show the surface morphologies of Sn substrate and Sn electrodeposited at various current densities for 5 s under galvanostatic conditions. The deposited Sn exhibited a dendritic structure, with multiple short secondary Sn rods extending from a long primary Sn rod. The diameters of the deposited Sn rods at each current density were quantified through image analysis and are summarized in Figure 1g. While the primary Sn rod diameter remained constant at approximately 1.35 \(\upmu\)m, the secondary Sn rod diameter increased linearly with current density, ranging from approximately 0.58 \(\upmu\)m at 1 A/cm\({}^{2}\) to 1.10 \(\upmu\)m at 5 A/cm\({}^{2}\). It is noted that the agglomeration of the secondary rods was observed at current densities above 4 A/cm\({}^{2}\) (yellow dashed circles in Figure 1e,f). This  
agglomeration is undesirable, as the study aims to utilize the 1-D micro rod morphology of Sn to mitigate volume change issues in LIB anode applications. In addition, when the Sn rods were electrodeposited for 10 s at current densities below 3 A/cm\({}^{2}\) to increase the deposition amount, a similar agglomeration of Sn rods was observed (yellow dashed circles in Figure 2a-c). This suggests that to obtain individually separated Sn rods under galvanostatic conditions, both current density and deposition time must be controlled within specific limits. From a practical standpoint, this indicates that large-scale production of Sn rods through constant-current electrodeposition is significantly constrained. Figure 3a-e show the surface morphologies of Sn electrodeposited at various voltages for 10 s under potentiostatic conditions. Similar to galvanostatic deposition, dendritic structures of primary and secondary Sn rods were observed. However, unlike in galvanostatic conditions, thin secondary rods were formed without agglomeration regardless of the applied voltage. The measured diameters of the Sn rods deposited at different voltages are shown in Figure 3f, indicating that both the primary and secondary rod diameters remained nearly constant irrespective of the applied voltage. Notably, the diameters of primary (approximately 1.28 \(\upmu\)m) and secondary (approximately 0.59 \(\upmu\)m) Sn rods were comparable to those of Sn rods electrodeposited at 1 A/cm\({}^{2}\) for 5 s (Figure 1a). To analyze the relationship between applied voltage and deposition amount, the electrodeposited  
Figure 1: SEM images of **(a)** Sn substrate and **(b–f)** Sn rods electrodeposited on the substrate for 5 s under various current densities: **(b)** 1, **(c)** 2, **(d)** 3, **(e)** 4, and **(f)** 5 A/cm\({}^{2}\). **(g)** Variations in the diameters of primary and secondary Sn rods with current density. Figure 2: SEM images of Sn rods electrodeposited on Sn substrate for 10 s under various current densities: **(a)** 1, **(b)** 2, and **(c)** 3 A/cm\({}^{2}\). material quantity was calculated from the current density-time profiles obtained during potentiostatic deposition (Figure 4). The results are summarized in Table 1.  
Figure 4: Variation in the current density with electrodeposition time at different voltages, measured during potentiostatic electrodeposition. Figure 3: SEM images of Sn rods electrodeposited on Sn substrate for 10 s under various voltages: (**a**) 4, (b) 5, (c) 6, (d) 7, and (e) 8 V. (**f**) Variations in the diameters of primary and secondary Sn rods with voltage. Compared to the Sn deposition amount under galvanostatic conditions at 1 A/cm\({}^{2}\) (10 C/cm\({}^{2}\), -6.16 mg Sn/cm\({}^{2}\)), the deposition amount under potentiostatic conditions increased from 6.83 C/cm\({}^{2}\) (-4.20 mg Sn/cm\({}^{2}\)) at 4 V to 33.92 C/cm\({}^{2}\) (-20.86 Sn/cm\({}^{2}\)) at 8 V.  
In summary, under galvanostatic conditions, the diameter of the secondary rods increased with increasing current density, leading to agglomeration and preventing the synthesis of well-separated Sn rods.