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

Abstract

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 LiNiO2 (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 Ni2+ 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, NaNiO2 (NNO) is prepared, showing no such defects due to larger differences in ionic radii between Ni2+/Ni3+ and Na+. NNO is then subjected to Na+/Li+ exchange under mild conditions. In so doing, monolithic LNO particles free of NiLi • 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.

Conformal Li2HfO3/HfO2 Nanoparticle Coatings on Layered Ni-Rich Oxide Cathodes for Stabilizing Interfaces in All-Solid-State Batteries

“…Despite the individual advantages of Ni-rich NCM CAMs and sulfide SEs, their practical combination in SSBs is faced with many challenges. The stability of NCM decreases with increasing Ni content, while residual lithium species and cation intermixing (Ni 2+ on lithium site) impair ion transport . Apart from that, the charge cutoff voltage of NCM cells surpasses the electrochemical stability window of sulfide SEs. − As a result, the NCM|SE interface suffers from degradation, resulting in impedance buildup.…”

Facile solid-state synthesis of a layered Co-free, Ni-rich cathode material for all-solid-state batteries

“…17 Note that the Li + ions may also migrate to the transition-metal layer, ultimately leading to Li/Ni intermixing (formation of Ni Li and Li Ni defects). 18,19 Rietveld analysis revealed a site disorder (Ni Li ) of about 3%, which is lower than that of a NMX material of “same” composition reported previously. 20…”

Stoichiometry matters: correlation between antisite defects, microstructure and magnetic behavior in the cathode material Li1−zNi1+zO2

“…This hypothesis is further strengthened by the fact that the NMR data from LiNiO 2 prepared by low temperature ion exchange from well-ordered NaNiO 2 (no Li + in the Ni layer) does not show a peak at 450 ppm. 21 The second explanation for the 450 ppm peak commonly encountered in the literature assumes the presence of a Ni 1− x Li x O, rock salt type phase with a large amount of Ni 2+ . 50 If present, the prominent cubic phase reflection 200 would be expected at 2 θ ≈ 23.0° ( e.g.…”

“…As shown recently, with low temperature, ion exchange-based synthesis of LNO from NaNiO 2 at around 320 °C instead of 700 °C, Li loss can be avoided. 21 The Ni Li defect is easily identied even in lab X-ray powder diffractometry due to the large additional electron density of nickel vs. lithium and thus routinely quantied in LNO studies. Another important defect, in which Ni and Li ] 3a [O 2 ] 6c , matches the denition of an antisite defect.…”