Representatives of the LixNi1−y−zCoyMnzO2 (NCM) family of cathode active materials (CAMs) with high nickel content are becoming the CAM of choice for high performance lithium‐ion batteries. In addition to high specific capacities, these layered oxides offer high specific energy, power, and long cycle life. Recently, the development of single crystalline particles of NCM has enabled even longer lifetimes due to achieving higher Coulomb efficiencies. In this work, the performance of NCM materials with different particle size and morphology is explored in terms of key parameters such as the charge‐transfer resistance and the chemical diffusion coefficient of lithium. Cracking of secondary particles leads to liquid electrolyte infiltration in the CAM, lowering the charge‐transfer resistance and increasing the apparent diffusion coefficient by more than one order of magnitude. In contrast, these effects are not observed with single‐crystalline NCM, which is mostly free of cracks after cycling. Consequently, severe kinetic limitations are observed when cycling large “uncracked” secondary particles at low potential and capacity. These results demonstrate that cracking of polycrystalline particles of NCM is not solely detrimental but helps to achieve high reversible capacities and rate capability. Thus, optimization of CAMs size and morphology is decisive to achieve good rate capability with high‐nickel NCMs.

In liquid electrolyte-type lithium-ion batteries, Nickel-rich NCM (Li1+x (Ni1−y−z Co y Mnz)1−x O2) as cathode active material allows for high discharge capacities and good material utilization, while solid-state batteries perform worse despite the past efforts in improving solid electrolyte conductivity and stability. In this work, we identify major reasons for this discrepancy by investigating the lithium transport kinetics in NCM-811 as typical Ni-rich material. During the first charge of battery half-cells, cracks form and are filled by the liquid electrolyte distributing inside the secondary particles of NCM. This drastically improves both the lithium chemical diffusion and charge transfer kinetics by increasing the electrochemically active surface area and reducing the effective particle size. Solid-state batteries are not affected by these cracks because of the mechanical rigidity of solid electrolytes. Hence, secondary particle cracking improves the initial charge and discharge kinetics of NCM in liquid electrolytes, while it degrades the corresponding kinetics in solid electrolytes. Accounting for these kinetic limitations by combining galvanostatic and potentiostatic discharge, we show that Coulombic efficiencies of about 89% at discharge capacities of about 173 mAh gNCM −1 can be reached in solid-state battery half-cells with LiNi0.8Co0.1Mn0.1O2 as cathode active material and Li6PS5Cl as solid electrolyte.

Emphasis was recently placed on the Cs2AgBiBr6 double perovskite as a possible candidate to substitute toxic lead in metal halide perovskites. However, its poor light-emissive features currently make it unsuitable for solid-state lighting. Lanthanides doping is an established strategy to implement luminescence in poorly emissive materials, with the additional advantage of fine-tuning the emission wavelength. We discuss here the impact of Eu-and Yb-doping on the optical properties of Cs2AgBiBr6 thin films, obtained from solution-processing of hydrothermally synthesized bulk crystalline powders, by combining experiments and density functional theory calculations. Eu(III) incorporation does not lead to the characteristic 5 D0→ 7 F2 emission feature at 2 eV, while only a weak trap-assisted sub band-gap radiative emission is reported. Oppositely, we demonstrate that incorporated Yb(III) leads to an intense and exclusive photoluminescence emission in the nearinfrared as a result of the efficient sensitization of the lanthanide 2 F5/2→ 2 F7/2 transition.

The use of solid electrolytes in lithium batteries promises to increase their power and energy density, but several challenges still need to be overcome. One critical issue is capacity-fading, commonly ascribed to various degradation reactions in the composite cathode. Chemical, electrochemical as well as chemo-mechanical effects are discussed to be the cause, yet no clear understanding of the mechanism of capacity fading is established. In this work, a model is proposed to interpret the low-frequency impedance of the cathode in terms of lithium diffusion within an ensemble of LiNi1−x−y Co x Mn y O2 (NCM) cathode active material particles with different particle sizes. Additionally, an electrochemical technique is developed to determine the electrochemically active mass in the cathode, based on the estimation of the state-of-charge via open circuit potential-relaxation. Tracking the length of lithium diffusion pathways and active mass over 40 charge-discharge cycles demonstrates that the chemo-mechanical evolution in the composite cathode is the major cause for cell capacity fading. Finally, it is shown that single-crystalline NCM is far more robust against chemo-mechanical degradation compared to polycrystalline NCM and can maintain a high cycling stability.

The application of nickel-rich LiNi x Co y Al z O 2 (NCA) cathode materials in solid-state lithium-ion batteries (SSBs) promises significant improvements in energy density, stability, and safety over traditional lithium-ion batteries with liquid electrolytes. However, low active mass utilization and strong capacity fading associated with degradation of the cathode often limit SSB applicability. The use of single-crystalline cathode active materials (CAMs) instead of spherical polycrystalline materials optimized for performance in lithium-ion batteries recently emerged as a promising approach in the field of SSBs to overcome this issue. In this work, single-crystalline LiNi 0.8 Co 0.15 Al 0.05 O 2 (SC-NCA) is investigated as cathode active material for SSBs. It is shown that appropriate postprocessing of assynthesized materials, which consists of washing steps with either water or ethanol followed by postannealing at different temperatures, is key to achieve high-performance cathodes. X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy are employed to characterize the effect of postprocessing on structure and morphology. The postprocessing procedure was tailored to mitigate detrimental side reactions that result in structural damage of the SC-NCA, while retaining the beneficial effects of deagglomeration and control of surface impurities. Washing with ethanol and subsequent postannealing at 750 °C allowed us to obtain SC-NCA materials that perform well in SSB cells with Li 6 PS 5 Cl as solid electrolyte, enabling a high initial discharge capacity of 174 mAh g −1 , good rate performance, and high capacity retention (94% after 200 cycles) at 25 °C.