(Invited) Nanostructured Rocksalt-Based Positive Electrode Materials for Rechargeable Li/Na Batteries

Abstract

In the past decade, lithium-enriched compounds, Li2MO3 (M = Mn4+, Ru4+ etc.), have been extensively studied for high-capacity positive electrode materials of lithium batteries. Although the origin of high reversible capacities was a debatable subject for a long time, recently it has been evidenced that charge compensation is partly achieved by solid-state redox of non-metal anions, i.e., oxide ions (anionic redox), coupled with redox reaction of transition metal ions (cationic redox), which is the basic theory used for classical lithium/sodium insertion materials. Recently, many cation-disordered rocksalt oxides have been proposed as a new series of electrode materials, which utilize reversible anionic redox. Nevertheless, insufficient electrode kinetics for the cation-disordered rocksalt system limits its use for practical applications. One simple strategy is to synthesize nanosized materials, which overcomes a problem of electrode kinetics (for electrons, holes and ions), and indeed electrode kinetics is significantly improved through nanosizing even for a non-lithium-excess and stoichiometric system.1) Moreover, Nanosized Li/Na-excess oxides also deliver large reversible capacities even at room temperature,2, 3) which shows much better electrode kinetics compared with as-prepared submicrometer-sized samples.From these findings, we discuss the advantages/disadvantages of “nanostructured” rocksalt-based electrode materialsto develop high energy Li/Na-ion batteries in the future.References Sato et al., and N. Yabuuchi., Journal of Materials Chemistry A, 6, 13943 (2018).Kobayashi et al., and N. Yabuuchi, Small, 15, 1902462 (6 pages) (2019).Kobayashi et al., and N. Yabuuchi, Materials Today, in-press, DOI: 10.1016/j.mattod.2020.03.002