Li, Q.; Ning, D.; Zhou, D.; An, K.; Schuck, G.; Wong, D.; Kong, W.; Schulz, C.; Schumacher, G.; Liu, X.: Tuning Both Anionic and Cationic Redox Chemistry of Li-Rich Li1.2Mn0.6Ni0.2O2 via a “Three-in-One” Strategy. Chemistry of Materials 32 (2020), p. 9404-9414
10.1021/acs.chemmater.0c03460

Abstract:
Anionic redox chemistry endows Li-rich layered oxide cathode with high specific capacity, but it also causes some critical issues such as voltage decay, structure degradation, and irreversible oxygen release. Herein, we propose to tune both the anionic and cationic redox chemistry of Li1.2Mn0.6Ni0.2O2 via a “three-in-one” strategy integrating Na doping for the Li site and Si substitution for the Mn and Na2SiO3 coating layer, which is achieved by the facile coating of Na+-conductive Na2SiO3. In comparison with the pristine or Li2SiO3-coating sample, the concerns of voltage fading, poor rate capability, structure degradation, and oxygen release have all been largely alleviated due to the “three-in-one” effect. First, the coating layer impedes the side reaction and the dissolution of transition metals (TMs). Second, Na+ is confirmed to be doped into the Li layers to facilitate the transport kinetics of lithium ions while Si4+ is doped into the TM site, which enhances the stability of the layered structure during cycling due to the strong Si−O bond and reduces the migration of TMs. Third, the integrated strategy also decreases the covalency of TM−O bonds, which is verified to improve the reversibility of anion redox chemistry and suppress oxygen evolution. The synergetic strategy sheds some light on exploring high-performance cathode materials by tuning both anionic and cationic redox chemistry.