# Li2O-Based Cathode Additives Enabling Prelithiation of Si Anodes
## 3 Results and Discussion  
### Impact of Milling Conditions on the Additive Performance  
SEM images of the three different Li\({}_{2}\)O additives prepared via planetary ball-milling (two different milling conditions (1100 rpm for 5 min vs. 400 rpm for 1 h) and with and without the Co\({}_{3}\)O\({}_{4}\) additive) are shown in Figure 1a. While all powders exhibited relatively wide particle size distribution, milling at higher revolutions per minute resulted in smaller particles with smoother edges (Li\({}_{2}\)O @1100 rpm vs. Li\({}_{2}\)O @400 rpm). When Co\({}_{3}\)O\({}_{4}\) was added (Li\({}_{2}\)O + Co\({}_{3}\)O\({}_{4}\) @400 rpm), it coated the surface of Li\({}_{2}\)O particles but did not seem to affect the milling process, as Li\({}_{2}\)O + Co\({}_{3}\)O\({}_{4}\) @400 rpm and Li\({}_{2}\)O @400 rpm showed similar particle size and shape. Once the additives were incorporated into the electrode (Figure S1), they distributed evenly among the NMC622 particles, which were \(\sim\)10 \(\upmu\)m in diameter. The preparation method and performance of all additive-containing electrodes tested in this work are summarized in Table 1.  
Half-cell voltage profiles of the three Li\({}_{2}\)O-containing electrodes and the baseline NMC622 electrode during the first charge are shown in Figure 1b. The cells were charged up to 4.7 V vs. Li/Li\({}^{+}\) and the profiles are plotted as a function of capacity per gram of NMC622 in the electrode. The same voltage profiles plotted as a function of mAh/cm\({}^{2}\) are shown in Figure S2. The additional capacity obtained from Li\({}_{2}\)O is labeled for each electrode (mAh/g\({}_{\text{L2O}}\)). These values were calculated assuming 250 mAh/g from NMC622, which is an empirical value from the baseline electrode. First, comparing the baseline electrode and Li\({}_{2}\)O@400 rpm, a plateau at \(\sim\)4.6 V was observed for Li\({}_{2}\)O@400 rpm, which corresponds to the reaction of Li\({}_{2}\)O [24], and 1156 mAh/g\({}_{\text{Li2O}}\) of additional capacity was obtained. When Li\({}_{2}\)O was milled at higher revolutions per minute, i.e., Li\({}_{2}\)O@1100 rpm, a greater capacity of 1900 mAh/g\({}_{\text{Li2O}}\) was obtained. Both electrodes showed the activation of Li\({}_{2}\)O starting at \(\sim\)4.6 V vs. Li/Li\({}^{+}\), although the Li\({}_{2}\)O@1100 rpm electrode showed \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Electrode** & **Additive Composition** & **Milling Condition** & **Capacity (4.7 V vs. Li/Li\({}^{+}\))** \\ \hline Li\({}_{2}\)O @400 rpm & Li\({}_{2}\)O & 400 rpm for 1 h & 1156 mAh/g\({}_{\text{L2O}}\) \\ Li\({}_{2}\)O @1100 rpm & Li\({}_{2}\)O & 1100 rpm for 5 min & 1900 mAh/g\({}_{\text{Li2O}}\) \\ Li\({}_{2}\)O + Co\({}_{3}\)O\({}_{4}\) @400 rpm & 3 Li\({}_{2}\)O + 1/3 Co\({}_{3}\)O\({}_{4}\) & 400 rpm for 1 h & 1163 mAh/g\({}_{\text{Li2O}}\) \\ Li\({}_{2}\)O + Co\({}_{3}\)O\({}_{4}\) @1100 rpm & 3 Li\({}_{2}\)O + 1/3 Co\({}_{3}\)O\({}_{4}\) & 1100 rpm for 5 min and 25 & 1504 mAh/g\({}_{\text{Li2O}}\) \\  & & min rest, repeated 4 times & 793 mAh/g\({}_{\text{Li2O}}\)+Co\({}_{3}\)O4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the electrodes examined in this work. Figure 1: (**a**) SEM images of additive powders and (**b**) half-cell voltage profiles of the additive-containing and baseline electrodes during the first charge. Half cells were charged at a C/20 rate up to 4.7 V at 30 \({}^{\circ}\)C. Voltage profiles are plotted as a function of grams of NMC in the electrode, excluding the mass of additives. Additional capacity obtained from the additives calculated per gram of Li\({}_{2}\)O in the electrodes is indicated inside the figures for each profile. about a 100 mV decrease in the plateau as the reaction proceeded. We note the theoretical capacity of Li\({}_{2}\)O, assuming its full conversion to 2 Li\({}^{+}\) + 2e\({}^{+}\) + \(\frac{1}{2}\)O\({}_{2}\), is 1794 mAh/g\({}_{\text{LI2O}}\).