Low-Temperature Ion Exchange Synthesis of Layered LiNiO₂ Single Crystals with High Ordering

Layered Ni-rich oxide cathode materials are being explored in an effort to boost the energy density of lithium-ion batteries, especially for automotive applications. Among them, the ternary-phase LiNiO 2 (LNO) is a promising candidate but brings along various issues, such as poor structural stability. The material is prone to disordering (Li off-stoichiometry) when prepared by conventional solid-state synthesis, leading to the presence of Ni 2+ in the Li layer. These point defects negatively affect the utilization of the Li inventory, thereby limiting the practical specific capacity. In this work, we report on a two-step synthesis approach that avoids the formation of nickel substitutional defects. First, NaNiO 2 (NNO) is prepared, showing no such defects due to larger differences in ionic radii between Ni 2+ /Ni 3+ and Na + . NNO is then subjected to Na + /Li + exchange under mild conditions. In so doing, monolithic LNO particles free of Ni Li • defects can be produced at relatively low temperatures. Notably, this route allows for tailoring of the grain size, a strategy that may be used to gain insights into the structure–size–property relations in single-crystalline LNO.