Synthesis of Li and Mn-Rich Layered Oxides as Concentration-Gradients for Lithium-Ion Batteries

Li and Mn-rich layered oxides, i.e. Li1+xM1-xO2 (M = Mn, Ni and Co), are attractive positive electrode materials for Li-ion batteries due to their promising high specific capacities. Unfortunately, these materials provide an energy-density fading due to a continuous voltage decay resulting from chemical instability of their surface structure upon cycling. The purpose of this paper is to discuss the main insights got from syntheses of materials targeted to be concentration-gradients of global compositions Li1+x(Ni0.29Mn0.53Co0.18)1-xO2 with: (i) Li and Mn-rich layered oxides in the core to deliver high capacity, and (ii) layered oxides enriched in Ni and in Co moving to the surface of the spherical aggregates to promote improved chemical and thermal stability for the electrode material. Concentration-gradient, core-shell or re-homogenized materials were obtained depending on the temperature and excess of lithium used for the high temperature thermal treatment (i.e. the second step of the synthesis). Despite complex to master, the engineering of layered oxide materials was shown to be a track to follow to optimize the performance of an electrode material.