For applications that require both high energy densities and a long cycle life with high safety standards from their batteries, lithium-ion batteries (LIBs) containing liquid electrolytes are still the cell chemistry of choice. The capacity limiting component in common LIBs is the lithium metal oxide cathode. The most prominent cathode material used for high energy density batteries are layered lithium nickel manganese cobalt oxides (NMCs), since they provide high capacity and high average voltages combined with good safety properties. However, the usage of Co and Ni in these materials comes with disadvantages due to their relative rarity in the earth crust which translates into high material costs and ethical dilemmas due to the labour conditions in Congolese Co-mines, where 1/2 to 3/4 of the worlds Co is mined. Co and Ni are indispensable materials in layered cathodes due to their electronic properties, which maintain the layer structure during cycling. For a long time, it was generally agreed that lithium conductivity only occurs in materials with ordered lithium structures. However, in 2014, Lee et al. succeeded in elucidating the Li+ ion transport mechanism in disordered materials, thereby expanding the field of potentially usable cathode materials.[1] Since then, much research has been devoted to the development of new disordered cathode materials. Much attention was paid to disordered rock salts with Li excess (DRXs), which now not only do not have to contain Ni and Co, but also enable the partial usage of F as an oxidizing species instead of O. While the development of new DRX materials with a wide variety of stoichiometric compositions has received a great deal of attention, the development of tailor-made electrolyte formulations for the new cathode types, especially in combination with graphite as the anode, has remained relatively unexplored.[1–4] The aim of our research is to address and close this research gap.
In this context, we investigate the formulations of a series of electrolytes, including localised high concentration electrolytes (LHCEs), under high voltage conditions (4,8 V vs. Li | Li+), in full (vs. graphite) and in half cells (vs. Li0). The cathode investigated is a highly fluorinated DRX (FDRX), of the stochiometric formula Li2.2Mn0.6Nb0.2O2F, which needs high voltage conditions to reach high capacities and therefore energy density since a lot of Li+ can be released from the material through oxygen redox at high voltages.