The layered oxides LiNi_xMn_yCo_zO₂ (NMCs, x + y + z = 1) with high nickel content (x ≥ 0.6, Ni-rich NMCs) are promising high-energy density-positive electrode materials for Li-ion batteries. Their electrochemical properties depend on Li⁺/Ni²⁺ cation disordering originating from the proximity of the Li⁺ and Ni²⁺ ionic radii. We synthesized a series of the LiNi₀.₈Mn₀.₁Co₀.₁O₂ NMC811 adopting two different disordering schemes: Ni for Li substitution at the Li site in the samples finally annealed in air, and close to Ni↔Li antisite disorder in the oxygen-annealed samples. The defect formation scenario was revealed with Rietveld refinement from powder X-ray diffraction data, and then the reliability of semi-quantitative parameters, such as I₀₀₃/I₁₀₄ integral intensity ratio and c/(2√6a) ratio of pseudocubic subcell parameters, was verified against the refined defect concentrations. The I₀₀₃/I₁₀₄ ratio can serve as a quantitative measure of g(Ni_Li) only after explicit correction of intensities for preferred orientation. Being normalized by the total scattering power of the unit cell, the I₀₀₃/I₁₀₄ ratio depends linearly on g(Ni_Li) for each disordering scheme. The c/(2√6a) ratio appears to be not reliable and cannot be used for a quantitative estimate of g(Ni_Li). In turn, the volume of the R$\overline{3}$m unit cell correlates linearly with g(Ni_Li), at least for defect concentrations not exceeding 5%. The microscopy techniques such as high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron diffraction tomography (EDT) allow us to study the materials locally, still, there is no proper quantitative approach for comprehensive analysis of defects. In the present work, the TEM-assisted quantitative Li⁺/Ni²⁺ disordering analysis with EDT and HAADF-STEM in six Ni-rich NMC samples with various defects content is demonstrated. Noteworthy, while PXRD and EDT methods demonstrate overall defect amounts, HAADF-STEM allows us to quantitatively distinguish regions with various disordering extents. Therefore, the combination of mentioned PXRD and TEM methods gives the full picture of Li⁺/Ni²⁺ mixing defects in Ni-rich NMCs.

Composite positive electrode materials (1−x) LiNi_0.8Mn_0.1Co_0.1O₂∙xLi₂SO₄ (x = 0.002–0.005) for Li-ion batteries have been synthesized via conventional hydroxide or carbonate coprecipitation routes with subsequent high-temperature lithiation in either air or oxygen atmosphere. A comparative study of the materials prepared from transition metal sulfates (i.e., containing sulfur) and acetates (i.e., sulfur-free) with powder X-ray diffraction, electron diffraction, high angle annular dark field transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy revealed that the sulfur-containing species occur as amorphous Li₂SO₄ at the grain boundaries and intergranular contacts of the primary NMC811 crystallites. This results in a noticeable enhancement of rate capability and capacity retention over prolonged charge/discharge cycling compared to their sulfur-free analogs. The improvement is attributed to suppressing the high voltage phase transition and the associated accumulation of anti-site disorder upon cycling and improving the secondary agglomerates’ mechanical integrity by increasing interfacial fracture toughness through linking primary NMC811 particles with soft Li₂SO₄ binder, as demonstrated with nanoindentation experiments. As the synthesis of the (1−x) LiNi_0.8Mn_0.1Co_0.1O₂∙xLi₂SO₄ composites do not require additional operational steps to introduce sulfur, these electrode materials might demonstrate high potential for commercialization.

Ni-rich layered transition metal (TM) oxides are considered to be the most promising cathode materials for lithium-ion batteries because of their high electrochemical capacity, high Li⁺ ion (de)intercalation potential, and low cobalt content. However, such materials possess several drawbacks including relatively low volumetric energy density caused by insufficient values of tap density. Herein, we demonstrate an exceptionally rapid and energy-saving synthesis of the mixed hydroxide precursor for the LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) positive electrode (cathode) material through a microwave-assisted hydrothermal technique. The obtained material further serves as a space-filler to fill the voids between spherical agglomerates in the cathode powder prepared via a conventional co-precipitation technique boosting the tap density of the resulting mixed NMC811 by 30% up to 2.9 g/cm³. Owing to increased tap density, the volumetric energy density of the composite cathode exceeds 2100 mWh/cm³ vs. 1690 mWh/cm³ for co-precipitated samples. The crystal structure of the obtained materials was scrutinized by powder X-ray diffraction and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM); the cation composition and homogeneity of TM spatial distribution were investigated using energy-dispersive X-ray spectroscopy in a STEM mode (STEM-EDX). Well-crystallized NMC811 with a relatively low degree of anti-site disorder and homogeneous TM distribution in a combination with the co-precipitated material delivers a reversible discharge capacity as high as ~200 mAh/g at 0.1C current density and capacity retention of 78% after 300 charge/discharge cycles (current density 1C) within the voltage region of 2.7–4.3 V vs. Li/Li⁺.