Electrochemical Splitting of Lif: A New Approach to Lithium-Ion Battery Materials

Introduction Lithium-ion batteries (LIB) are the electrochemical storage systems with the highest energy density, which is yet insufficient for many applications. State of the art cathodes applied in the modern LIB rely on intercalation type of electrochemical reactions. However, intercalation type materials have already reached maturity and further significant increase in their energy density is unlikely. On the other hand, Li binary compounds with high formation energies may offer another approach to the electrochemical energy storage. Table 1 compares the Gibbs free energies and the theoretical discharge capacities of several binary lithium compounds [1]. Both Li2O and Li2O2 are considered in the Li-air technology. However, despite its higher energy density Li2O cannot be split electrochemically [2, 3]. Recent study has evidenced electrochemical splitting of LiF and reversible Li extraction and insertion was observed of FeF2 blended with LiF at the nanoscale [4]. This cathode is a mixture of lithium-ion host (LiF) and transition metal host (FeF2). During the first charge, FeF2+LiF mixture transforms into FeF3. First discharge transforms it into LiFeF3-like further undergoing reversible Li + reinsertions. We have expanded this study and show that LiF can be split electrochemically in the presence of other redox hosts, able to act as F acceptors. In this case, we have used four manganese oxides as redox hosts; MnO, Mn3O4, Mn2O3, and MnO2.