## 3 Results and Discussion
All of the lithiated SiO\({}_{2}\) electrodes exhibit the similar potential plateaus around 0.45 V, indicating the same active materials (Li\({}_{x}\)Si) of the electrodes and their high crystallinity, consistent with the XRD results. The prelithiation capacities of the SiO\({}_{2}\) particles are 1972, 2267, 1776, and 1412 mAhg\({}^{-1}\), which are listed in Table 1. Here, the prelithiation capacity is determined by subtracting the lithiation capacity from the delithiation capacity at the first cycle. The thermal lithiation can effectively compensate for the huge irreversible lithium loss during the first cycles via the formation of lithium silicates and Li\({}_{2}\)O. The cyclic voltammetry (CV) tests are conducted for both the pristine and prelithiated SiO\({}_{2}\) half cells for 3 consecutive cycles between 3.0 V and 0.01 V at a scan rate of 0.05 mVs\({}^{-1}\) (Figure 4). The pristine SiO\({}_{2}\) electrode exhibits cathodic peaks above 1.0 V corresponding to the irreversible electrochemical reactions between the SiO\({}_{2}\) and Li, which disappears in the subsequent cycles. The cathodic peak below 0.2 V can be ascribed to the lithiation process of silicon. The electrochemical equations can be expressed as followed:  
\[\text{SiO}_{2}+4\text{Li}^{+}+4\text{e}^{-}\rightarrow\text{2 Li}_{2}\text{O} +\text{Si} \tag{1}\]  
\[2\text{SiO}_{2}+4\text{Li}^{+}+4\text{e}^{-}\rightarrow\text{Li}_{4}\text{ SiO}_{4}+\text{Si} \tag{2}\]  
\[5\text{SiO}_{2}+4\text{Li}^{+}+4\text{e}^{-}\
i 2\text{Li}_{2}\text{Si}_{2} \text{O}_{5}+\text{Si} \tag{3}\]  
For the Li\({}_{x}\)Si/Li\({}_{2}\)O-4 anode, the corresponding peak of silicon lithiation is very pronounced. The cathodic peak at 0.5 V at the first cycle confirms the formation of highly crystalline Li\({}_{x}\)Si. Two distinct anodic peaks at about 0.34 and 0.51 V during the second and third cycle agree with the characteristic peaks of delithiation process from amorphous Li\({}_{x}\)Si to Si. The electrochemical equation can be expressed as followed:  
\[\text{Si}+\text{xLi}^{+}+\text{xe}^{-}\
i L_{x}\text{Si} \tag{4}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Electrode**} & **1 st Delithiation** & **Prelithiated** & **25 th Delithiation** & **50 th Delithiation** \\  & **Capacity/mAhg\({}^{-1}\)** & **Capacity/mAhg\({}^{-1}\)** & **Capacity/mAhg\({}^{-1}\)** & **Capacity/mAhg\({}^{-1}\)** \\ \hline Li\({}_{x}\)Si/Li\({}_{2}\)O-1 & 2537 & 1972 & 795 & 673 \\ Li\({}_{x}\)Si/Li\({}_{2}\)O-2 & 2590 & 2267 & 900 & 913 \\ Li\({}_{x}\)Si/Li\({}_{2}\)O-3 & 2259 & 1776 & 1135 & 870 \\ Li\({}_{x}\)Si/Li\({}_{2}\)O-4 & 1859 & 1412 & 1510 & 1323 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cycling performance for Li\({}_{x}\)Si/Li\({}_{2}\)O electrodes. Figure 4: Cycling voltammetry measurement of SiO\({}_{2}\) electrodes before (**a**) and after (**b**) prelithiation. The corresponding Nyquist plots measured at the first cycle are illustrated in supplement information (SI, Figure S2). Li\({}_{x}\)Si/Li\({}_{2}\)O-4 anode demonstrated a smaller semicircle than the corresponding SiO\({}_{2}\) anode, indicating a lower charge transfer resistance (Rct). It is clear that the prelithiated sample provides a fast electron transport pathway between the Li\({}_{x}\)Si domains in the microparticles. The cycling performance of prelithiated SiO\({}_{2}\) composites is shown in Figure 5a and listed in Table 1. The Li\({}_{x}\)Si/Li\({}_{2}\)O composites deliver a first delithiation capacity of around 2000 mAhg\({}^{-1}\) at C/20, with a corresponding Coulombic efficiency (CE) that is above 90% at initial cycles (Figure 5a and Figure S3). Very interestingly, the Li\({}_{x}\)Si/Li\({}_{2}\)O-4 anode, prepared from micron-sized silica, has the best cycling stability among the four samples. It is able to maintain a stabilized reversible capacity of around 1300 mAhg\({}^{-1}\) with acceptably small decay (~71% capacity retention) after prolonged 50 cycles.