Conformal coating of nm-thick Al₂O₃ layers on electrode material is an effective strategy for improving the longevity of rechargeable batteries. However, solid understanding of how and why surface coatings work the way they do has yet to be established. In this article, we report on low-temperature atomic layer deposition (ALD) of Al₂O₃ on practical, ready-to-use composite cathodes of NCM622 (60% Ni), a technologically important material for lithium-ion battery applications. Capacity retention and performance of Al₂O₃-coated cathodes (≤10 ALD growth cycles) are significantly improved over uncoated NCM622 reference cathodes, even under moderate cycling conditions. Notably, the Al₂O₃ surface shell is preserved after cycling in full-cell configuration for 1400 cycles as revealed by advanced electron microscopy and elemental mapping. While there are no significant differences in terms of bulk lattice structure and transition-metal leaching among the coated and uncoated NCM622 materials, the surface of the latter is found to be corroded to a much greater extent. In particular, detachment of active material from the secondary particles and side reactions with the electrolyte appear to lower the electrochemical activity, thereby leading to accelerated capacity degradation.

High figure-of-merit achieved in Ag–Se-based n-type printed film due to the formation of the β-Ag ₂ Se phase via thermally stimulated dissociative adsorption.

Li-rich disordered rock-salt oxides such as Li_1.2Ni_1/3Ti_1/3Mo_2/15O₂ are receiving increasing attention as high-capacity cathodes due to their potential as high-energy materials with variable elemental composition. However, the first-cycle oxygen release lowers the cycling performance due to cation densification and structural reconstruction on the surface region. This work explores the influence of lithium excess on the charge compensation mechanism and the effect of surface modification with LiNbO₃ on the cycling performance. Moving from a stoichiometric LiNi_0.5Ti_0.5O₂ composition toward Li-rich Li_1.2Ni_1/3Ti_1/3Mo_2/15O₂, oxygen redox is accompanied by oxygen release. Thereby, cationic charge compensation is governed by the Ni^2+/3+ and Mo^3+/6+ redox reaction. Contrary to the bulk oxidation state of Mo⁶⁺ in the charged state, a mixed Mo valence on the surface is found by XPS. Furthermore, it is observed that smaller particle sizes result in higher specific capacities. Tailoring the surface properties of Li_1.2Ni_1/3Ti_1/3Mo_2/15O₂ with a solid electrolyte layer of LiNbO₃ altered the voltage profile, resulting in a higher average discharge voltage as compared to the unmodified material. The results hint at the interdiffusion of cations from the metal oxide surface coating into the electrode material, leading to bulk composition changes (doping) and a segregated Nb-rich surface. The main finding of this work is the enhanced cycling stability and lower impedance of the surface-modified compound. We argue that surface densification is mitigated by the Nb doping/surface modification.

Lithium‐thiophosphate‐based all‐solid‐state batteries (ASSBs) are increasingly attracting attention for high‐density electrochemical energy storage. In this work, the cycling performance of single and polycrystalline forms of LiNi_xCo_yMn_zO₂ (NCM, with ≥83% Ni content) cathode active materials in ASSB cells with an Li₄Ti₅O₁₂ composite anode is explored, and the advantages and disadvantages of both morphologies are discussed. The virtual lack of grain boundaries in the quasi‐single‐crystalline material is found to contribute to improved stability by eliminating the tendency of Ni‐rich NCM particles to crack during cycling, due to volume differences between the lithiated and delithiated phases. Although the higher crack resistance mitigates effects of chemical oxidation of the lithium thiophosphate solid electrolyte, the cells suffer from electrochemical side reactions occurring at the cathode interfaces. However, coating the single‐crystal particles with a protective LiNbO₃ overlayer helps to stabilize the interface between cathode active material and solid electrolyte, leading to a capacity retention of 93% after 200 cycles (with q_dis ≈ 160 mAh g_NCM⁻¹ or 1.7 mAh cm⁻² at C/5 rate and 45 °C). Overall, this work highlights the importance of addressing electro‐chemo‐mechanical phenomena in ASSB electrodes.