Boosting the capability of Li2C2O4 as cathode pre-lithiation additive for lithium-ion batteries

Li2C2O4, with a high theoretical capacity of 525 mAh·g−1 and good air stability, is regarded as a more attractive cathode pre-lithiation additive in contrast to the reported typical inorganic pre-lithiation compounds which are quite air sensitive. However, its obtained capacity is much lower than the theoretical value and its delithiation potential (> 4.7 V) is too high to match with the most commercial cathode materials, which greatly impedes its practical application. Herein, we greatly improve the pre-lithiation performance of Li2C2O4 as cathode additive with fulfilled capacity at a much-reduced delithiation voltage, enabling its wide applicability for typical commercial cathodes. We increase the capacity of Li2C2O4 from 436 to 525 mAh·g−1 by reducing its particle size. Through optimizing the types of conductive additives, introducing nano-morphological NiO, MnO2, etc. as catalysts, and innovatively designing a bilayer electrode, the delithiation potential of Li2C2O4 is successfully reduced from 4.778 to 4.288 V. We systematically study different particle size, conductive additives, and catalysts on the delithiation behavior of Li2C2O4. Finally, it is applied to pre-lithiate the hard carbon anode, and it is found that Li2C2O4 could effectively increase the capacity of the full cell from 79.0 to 140.0 mAh·g−1 in the first cycle. In conclusion, our study proves that improving the reactivity is an effective strategy to boost the pre-lithiation of Li2C2O4.