Highly reversible Ti/Sn oxide nanocomposite electrodes for lithium ion batteries obtained by oxidation of MAX Ti3AlxSn1-xC2 phases

Among the materials for the negative electrodes in Li-ion batteries, oxides capable of reacting with Li+ via intercalation/conversion/alloying are extremely interesting due to their high specific capacities but suffer from poor mechanical stability. A new way to design nanocomposites based on the Ti/SnOx system is the partial oxidation of the tin-containing MAX phase of Ti3Al(1-x)SnxO2 composition. Exploiting this strategy, we develop composite electrodes of Sn/TiOx and MAX phase capable of withstanding over 600 cycles in half cells with charge efficiencies higher than 99.5% and specific capacities comparable to those of graphite and higher than lithium titanate (Li4Ti5O12) electrodes. These unprecedented electrochemical performances are also demonstrated at full cell level in the presence of a low cobalt content layered oxide and explained through an accurate chemical, morphological and structural investigation which reveals the intimate contact between the MAX phase and the oxide particles. During the oxidation process, electroactive nanoparticles of TiO2 and Ti(1-y)SnyO2 nucleate on the surface of the unreacted MAX phase which therefore acts both as a conductive agent and as a buffer to preserve the mechanical integrity of the oxide during the lithiation and delithiation cycles.