# Intercalating Sn/Fe Nanoparticles in Compact Carbon Monolith for Enhanced Lithium Ion Storage
## 3 Results and Discussion
Among all electrodes, SFO presents the worst rate capability with an average capacity of 552, 282, and 138 mAh g\({}^{-1}\) at 0.2, 0.4, and 0.8 A g\({}^{-1}\), respectively, and hardly delivers the capacity at 1.6 and 3.2 A g\({}^{-1}\), proving that the carbon matrix is indispensable for improving the rating performance, especially under high current rates. It is worth emphasizing that, even after a light cycling at a large current density of 3.2 A g\({}^{-1}\) for several cycles, the reversible capacity of SFO cannot immediately be recovered when the current is reset at  
0.2 A g\({}^{-1}\), which exclusively proves a poor rate capability. Generally, the rate capability of the electrode material is closely related to the kinetics of electrochemical reactions, including the charge transfer and the Li\({}^{+}\) ion diffusion. The outstanding rate capability of SFO@C-400 most possibly results from its unique protection nanostructure and the refined crystals. The uniform carbon layer is able to function as a greatly conducting matrix. The ultrasmall SnO\({}_{2}\) nanoparticles can shorten the transport distance for both electrons and lithium ions. As a result, the faster charge transfer and Li\({}^{+}\) ions diffusion enable Li ions to be intercalated into more particles particularly at high current densities [63; 64]. The data show that the SFO@C-400 composite could endure the altered discharge current densities and possess a superior application prospect in high power LIBs. Figure 4: Electrochemical properties: (**a**) initial discharge/charge curves scanned at 0.2 A g\({}^{-1}\); (**b**) CV curves of SFO@C-400 at 0.1 mV s\({}^{-1}\); (**c**) rate capability at various current densities from 0.2 to 3.2 A g\({}^{-1}\); (**d**) cycling stability of 100 cycles at 0.2 A g\({}^{-1}\); (**e**) long-term cyclic life up to 200 cycles at 1 A g\({}^{-1}\). Figure 4d compares cyclabilities of all samples to gain the in-depth insights into the momentous role of structural design in influencing the Li ion storage properties of electrode substances. The electrochemical stability was examined under galvanostatic cycling, in a voltage range of 0.005-3.0 V at 0.2 A g\({}^{-1}\). Because of creation of SEI layers and unavoidable electrolyte decomposition, the delivered discharge-specific capacity falls notably during the early several cycles and tends to be stable in subsequent cycles. Despite being subjected to a capacity fading, SFO@C-400 delivers the considerably better Li ion storage capacity throughout entire cycles than other three samples, indicating the best cyclic stability. The SFO electrode suffers from most severe reversible capacity loss, maintaining only 132 mAh g\({}^{-1}\) (about 15.6% retention of the second discharge capacity) after 50 cycles, indicating the important role of carbon matrix in improving the cyclic performance. In sharp contrast, the cyclic performance of SFO@C-350, SFO@C-400, and SFO@C-450 exhibits a great improvement. After 100 cycles, the discharge capacity is stabilized at 411 mAh g\({}^{-1}\) for SFO@C-350, 519 mAh g\({}^{-1}\) for SFO@C-450,  
Figure 5: Differential charge capacity curves at 0.2 A/g of (**a**) the SFO@C-400 electrode and (**b**) the SFO electrode at the 1 st, 2 nd, 10 th, and 50 th cycle; reversible capacities versus cycle number of (**c**) the SFO electrode and (**d**) the SFO@C-400 electrode separated into potential ranges of 0.005–1.0 V and 1.0–2.5 V; SEM images of the SFO@C-400 electrode (**e**) before and (**f**) after 100 cycles at 0.2 A/g. but 726 mAh g\({}^{-1}\) for SFO@C-400, corresponding to a 55%, 54%, and 84% capacity retention of from the second discharge capacity to the 100 th cycle, respectively. This value of SFO@C-400 after 100 values is about two times more than the theoretical capacity of graphite and very close to theoretical value of SnO\({}_{2}\) (781 mAhhg\({}^{-1}\)).