# Intercalating Sn/Fe Nanoparticles in Compact Carbon Monolith for Enhanced Lithium Ion Storage
## 3 Results and Discussion
Besides, the better transfer kinetics of the Li\({}^{+}\) ions into Sn in the course of de-alloying could likewise contribute to the more excellent capacity retention in the de-alloying segment. In nature, as for SFO, the rapidly decaying segmentalized capacity unearths that a big deal of electric energy undergoes an irreversible dissipation within electrodes in the course of (de-)conversion events. The substantial rise of the surface/interp phase boundaries and structural stresses experienced within SnO\({}_{2}\) in the course of the lithium insertion and extraction reactions can elucidate the huge electricity depletion [66; 67]. The change in the surface areas caused by both the new component (Sn and Li\({}_{2}\)O) generation and the occurrence of micro-/nano-fractures triggers off the great surface and interface energy at the cost of electricity conserved through the conversion actions. Such phenomena bring about the poor energy efficacy of the SFO specimen cycled in 0.005-3 V and 1-3 V. The very elevated Gibbs free energy status of the nanotextured Sn/L\({}_{2}\)O hybrids renders them unsteady, thereby leading Sn to synchronically coarsen and diffuse onto the surfaces of the Li\({}_{2}\)O substrate or the carbon matrix within the lithiated electrode to maximally lower the surface and interface energy [35; 68]. The well-acknowledged battery degradation mechanism has evidenced that the giant structural stress intensification on the electrode surface underlies the drastic volume change during the dealloying-alloying process, finally sparking off a serious pulverization and crushing of SnO\({}_{2}\) electrodes and so the notorious capacity fading. The extremely stable segmentalized charge capacity at 0.005-1.0 V for SFO@C-400 unambiguously pinpoints the effective stress management and superb structural stability, as further affirmed by SEM image of the SFO@C-400 electrode before and after 100 cycles (Figure 5e,f). It can be spotted that a continuous layer of the SEI film tightly covers the electrode surfaces and no palpable cracking transpires to SEI films after 100 cycles, unveiling a stable SEI layer and no disintegration/exfoliation of the electrode materials during cycling. More significantly, the whole electrode remains intact after repeated volume changes, further certifying the eminent morphological robustness of the SFO@C-400 electrode and explaining reasons for its good cyclic function. The disparity in the kinetics of electrochemical reactions between the SFO@C electrodes and SFO electrode after the first cycle is further revealed via performing electrochemical impedance spectra (EIS) measurement (Figure 6). The spectra of all samples are made up of the arc in the high-frequency regions, the semicircle at high-medium frequencies, and the linear line at lower frequencies, which correspond to resistance of SEI layer (R\({}_{\text{SEI}}\)), charge transfer resistance (R\({}_{\text{ct}}\)) on the electrode-electrolyte interphase and the Warburg impedance related to the Li\({}^{+}\) diffusion process, respectively [69; 70]. The depressed half-loop at high frequency of SFO@C (particularly SFO@C-400) is substantially smaller than that of SFO, substantiating the enhanced electronic conductivity and rate capability. Markedly, EIS curves of SFO features two obvious semicircles, highlighting the gradual SEI layer generation on the electrode surfaces at the elevated frequency regions. Although the SEI layer formation can terminate the further electrolyte decomposition, provide the expedient passages for the Li\({}^{+}\) migration, and hence favor the rating behavior, its giant accumulation and progressive thickening will militate against the initial coulombic efficiency and lengthen the Li\({}^{+}\) transfer distance [71]. The R\({}_{\text{SEI}}\) value can likewise be diminished via a carbon coating because of circumvention of the direct contact between SnO\({}_{2}\) and electrolyte, thereby oppressing the occurrence of side reactions around interface boundaries.