# Li2O-Based Cathode Additives Enabling Prelithiation of Si Anodes
## 4 Conclusions  
In this work, we examined Li\({}_{2}\)O as a potential cathode additive for providing an additional Li source in order to compensate for the first-cycle Li loss, which is a well-known problem with Si-based anodes. By utilizing an OER catalyst, Co\({}_{3}\)O\({}_{4}\), to facilitate the oxidation of Li\({}_{2}\)O and ball-milling the Co\({}_{3}\)O\({}_{4}\) and Li\({}_{2}\)O mixtures, we showed these additives can deliver 1116 mAh/g\({}_{\text{Li2O}}\) or 589 mAh/g\({}_{\text{Li2O+Co3O4}}\) when charged up to 4.3 V vs. Li/Li+. Decreasing the Li\({}_{2}\)O particle size increased the utilization of Li\({}_{2}\)O, and the presence of Co\({}_{3}\)O\({}_{4}\) lowered the overpotential for Li\({}_{2}\)O activation. However, the electrode suffered from degradation caused by extensive electrolyte decomposition potentially involving reactive oxygenated species created as intermediates of Li\({}_{2}\)O oxidation. Utilizing the proposed successful, easily manufacturable additive, future work will involve (1) developing electrolytes to overcome this degradation issue, (2) designing electrodes to minimize the cell energy density loss, and (3) testing full cells with more controlled parameters (e.g., negative-to-positive (N/P) ratios, voltage range, and different anode and cathode pairs). The following are available online at [[https://www.mdpi.com/article/10.3390/app112412027/s1](https://www.mdpi.com/article/10.3390/app112412027/s1)]([https://www.mdpi.com/article/10.3390/app112412027/s1](https://www.mdpi.com/article/10.3390/app112412027/s1)), SEM Images of Li\({}_{2}\)O-containing electrodes, half-cell voltage profiles plotted as a function of areal capacity, 4.7 V charge profile of Li\({}_{2}\)O + Co\({}_{3}\)O\({}_{4}\) @1100 rpm electrode, XRD and XPS analysis of Li\({}_{2}\)O + Co\({}_{3}\)O\({}_{4}\) milled at 400 and 1100 rpm, areal capacity of full-cell electrodes, full-cell cycle performance, analysis of cycled electrodes, and impact of the upper cutoff voltage. SEM images of electrodes containing the Li\({}_{2}\)O additives. Larger particles (-10 \(\upmu\)m diameter) are NMC622 and the inset images show closer view of the additive particles. Figure S2. 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 mAh/cm\({}^{2}\). Figure S3. Half-cell voltage profiles of the baseline and Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @1100 rpm electrodes during the first charge at a C/20 rate up to 4.7 V plotted as a function of g of NMC in the electrode, excluding the mass of additives. Figure S4. XRD spectra of (a) baseline, (b) Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @400 rpm, and (c) Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @1100 rpm electrodes. Reference powder XRD patterns of NMC622 (#291468), Co\({}_{3}\)O\({}_{4}\) (#9362), and Li\({}_{2}\)O (#54368) are from the Inorganic Crystal Structure Database (ICSD). Figure S5. XPS spectra of (a) baseline, (b) Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @400 rpm, and (c) Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @1100 rpm electrodes. Ni 2p, Co 2p, and Mn 2p core levels are shown. Figure S6. Areal capacities of the (a) cathode (baseline and Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @1100 rpm electrodes) and (b) Si anode measured in half-cells. Cathodes were cycled between 3.0-4.7 V with a 0.10 mA/cm\({}^{2}\) current density and the Si anode was cycled between 0.05-0.75 V with a 0.15 mA/cm\({}^{2}\) current density. First cycle profiles are shown. Figure S7. Cycle performance of Baseline/Si and Li\({}_{2}\)O+Co\({}_{3}\)O\({}_{4}\) @1100 rpm/Si full cells. Charge and discharge capacity per g of NMC in the electrode, excluding the mass of additives, are plotted as a function of cycle number. Cells were cycled at C/20 rate for three cycles, then C/3 rate for 20 cycles, and finally at C/20 rate for three cycles between 3.0 and 4.6 V. Figure S8.