General flux-free synthesis of single crystal Ni-rich layered cathodes by employing a Li-containing spinel transition phase for lithium-ion batteries

Abstract

Single crystal cathodes with good structural stability and high volumetric energy-density have attracted considerable attention in lithium-ion batteries (LIBs). However, the general flux-free synthesis of single crystal Ni-rich cathodes is still very challenging because it requires overcoming the differences in thermodynamic stability of lithium-containing ternary metal oxide components and improving the kinetics of crystal growth during solid-state reactions. Herein, lithium-containing spinel oxide is introduced as a transition phase to overcome these issues in the synthesis of single crystal Ni-rich cathodes. Density functional theory calculations demonstrate that the spinel phase has much lower formation energy and higher thermal stability than the layered phase. Thus, the innovative introduction of the spinel phase availably enhances the kinetics of crystal growth and avoids the phase segregation of the NiO rock-salt phase. Single crystal Ni-rich Li[Ni_0.6Co_0.2Mn_0.2]O₂ and Li[Ni_0.8Co_0.1Mn_0.1]O₂ are synthesized by the further reaction of the-said spinel phase with Ni and Li sources. The former single crystal cathode shows improved cycling stability and thermal properties compared with those of the polycrystalline cathode. The full cells composed of this single crystal positive and mesocarbon microbead negative present high energy-density and a long-term lifespan. This proposed strategy offers a general approach to the preparation of single crystal Ni-rich cathodes for advanced LIBs.