# Electochemically Engineered Mesoporous Sn-Oxide Rods for Anode Materials in Lithium-Ion Batteries
## 3 Results and Discussion
### Electrochemical Properties of Core (Sn Rod)-Shell (Mesoporous Sn-Oxide Layer) Anodes  
The electrochemical properties of the core-shell anodes anodized at 6, 8, and 10 V were analyzed to investigate the influence of the pore size and wall thickness of Sn-oxide on electrode performance. The cyclic voltammograms presented in Figure 8a-c show a cathodic peak at approximately 0.5-0.8 V vs. Li\({}^{+}\)/Li during the first cathodic scan (denoted as A in the figures) for all three samples. This peak is attributed to the formation of a solid electrolyte interphase (SEI) layer and the reduction of SnO to Sn, leading to the formation of Li\({}_{2}\)O (SnO + 2 Li\({}^{+}\) + 2e\({}^{-}\)\(\rightarrow\) Sn + Li\({}_{2}\)O) [40,41]. Figure 8: Cyclic voltammograms of core-shell anodes anodized at **(a)** 6, (b) 8, and (c) 10 V. The measurements were performed at a scan rate of 1 mV/s in the voltage range of 0.01-3 V vs. Li\({}^{+}\)/Li. Representative cathodic peaks (A–C) and their pared anodic peaks (B’ and C’) are marked in the graphs. Figure 6: EDS spectra and chemical compositions of the Sn-oxide on the Sn rods at different anodization voltages: (a) 4, (b) 5, and (c) 6 V. (d) XRD patterns of the Sn rod and anodized Sn rods. From bottom to top: electrodeposited Sn rod, Sn rods anodized at 6 V, 8 V, and 10 V, respectively. Figure 7: Cross-sectional morphology of core-shell rods anodized at **(a)** 6, (b) 8, and (c) 10 V.  
The cathodic peak at around 0.01 V vs. Li\({}^{+}\)/Li and the anodic peak at around 0.83 V vs. Li\({}^{+}\)/Li (denoted as B and B\({}^{\prime}\), respectively, in the figures) represent the reversible lithiation and delithiation reactions of Sn (Sn + xLi\({}^{+}\) + xe\({}^{-}\) \(\leftrightarrow\) Li\({}_{x}\)Sn). In addition, a cathodic peak (denoted as C in the figures) appeared at approximately 1.10 V vs. Li\({}^{+}\)/Li during the second and third cathodic scans, related to the reduction of SnO to Sn and the formation of Li\({}_{2}\)O. The corresponding anodic peak (denoted as C\({}^{\prime}\) in the figures) appeared around 1.58 V vs. Li\({}^{+}\)/Li. [42; 43; 44]. This pair of redox peaks (C and C\({}^{\prime}\)) suggests that the Li\({}_{2}\)O formed in the first cycle is not completely irreversible and participates in the reaction to a certain extent reversibly in subsequent cycles. The prominence of this peak increased with higher anodization voltages, as seen in peaks C and C\({}^{\prime}\) of Figure 8a-c. This additional reversible process is expected to contribute to the increase in the reversible capacity of the active materials. Figure 9a-c present the charge and discharge curves for the first three cycles of the core-shell anodes anodized at 6, 8, and 10 V, which were tested as anode active materials. For comparison, the charge and discharge curves of the Sn rod anode are shown in Figure 9d. The initial charge capacities of the core-shell anodes anodized at 6, 8, and 10 V were 1395, 1479, and 1566 mAh/g, respectively, which were significantly higher than that of the Sn rod anode (907 mAh/g). These initial charge capacities included the aforementioned contributions from the SEI formation and Li\({}_{2}\)O generation. During the first charge, a voltage plateau was observed at approximately 1.3 V vs. Li\({}^{+}\)/Li, followed by a sloping region between 1.3 and 0.65 V vs. Li\({}^{+}\)/Li corresponding to Li\({}_{2}\)O formation (dotted squares in the figures) [42; 45; 46]. The voltage plateau became more pronounced at higher anodization voltage, leading to an increase in charge capacity. This trend is likely due to the thicker Sn-oxide layer formed at higher voltages, which promotes greater Li\({}_{2}\)O formation during the charging process. Figure 9: Charge and discharge curves for the initial three cycles at a rate of 50 mA/g: core-shell anodes anodized at (**a**) 6, (**b**) 8, and (**c**) 10 V. (**d**) Sn rod anode.