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.

CAM) in its lithiated form, that is, as present in a discharged cell. In its delithiated form, when the cell is charged, it is the only cell component that is contributing to storing energy (in conjunction with a hypothetical in situ lithiumplated anode formed during charging), thus making it the material required to be present in large quantity to achieve a high-performing cell. All other components, which may be required for large scale processing, only decrease the specific energy of the cell and are, therefore, engineered to minimize their content without affecting the function of the cell. This is evident in the research efforts made to increase the CAM content in the cathode layer, decrease the separator thickness as much as possible, and the pursuit to plate lithium metal in situ (in "anode-free" cells, which are more correctly described as "zero excess lithium metal" cells) without the use of an anode active material. [4] Thus, the CAM type and content in the cell ultimately determine the maximum specific energy that the system can provide.Moreover, the CAM contributes a significant proportion to the overall cell costs, [5] hence the necessity of steady tailoring toward reduced costs and higher energy density. So far, CAM development has mainly targeted performance optimization with LEs in LIBs. For instance, cathode electrolyte interface (CEI) formation, [6] Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today's lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes stateof-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed.

Solid-state batteries have gained increasing attention with the discovery of new inorganic solid electrolytes, some of which rival the ionic conductivity of liquid electrolytes. With the additional benefit of being...

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.

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.

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Solid-state batteries (SSBs) with high-voltage cathode active materials (CAMs) such as LiNi 1À xÀ y Co x Mn y O 2 (NCM) and poly(ethylene oxide) (PEO) suffer from "noisy voltage" related cell failure. Moreover, reports on their long-term cycling performance with high-voltage CAMs are not consistent. In this work, we verified that the penetration of lithium dendrites through the solid polymer electrolyte (SPE) indeed causes such "noisy voltage cell failure". This problem can be overcome by a simple modification of the SPE using higher molecular weight PEO, resulting in an improved cycling stability compared to lower molecular weight PEO. Furthermore, X-ray photoelectron spectroscopy analysis confirms the formation of oxidative degradation products after cycling with NCM, for what Fourier transform infrared spectroscopy is not suitable as an analytical technique due to its limited surface sensitivity. Overall, our results help to critically evaluate and improve the stability of PEO-based SSBs.

Single-crystalline Ni-rich LiNi1-x-y Co x Mn y O2 (SC-NCM) cathode active materials promise to increase the lifetime of high energy Li-ion batteries. SC-NCM consist of large primary particles that offer low surface area, limiting detrimental chemical reactions while exhibiting high morphological stability. A typical SC-NCM synthesis starts from the same Ni1-x-y Co x Mn y (OH)2 and LiOH∙H2O precursors commonly used for conventional spherical poly-crystalline NCM (PC-NCM), but requires higher temperatures and additional post-processing. Consequently, the cost and environmental impact of the production of Ni-rich SC-NCM is higher compared to the production of PC-NCM. In this study, we demonstrate a synthesis of SC-NCM that does not require the same highly engineered precursors as used for PC-NCM. We propose a more energy-efficient and cost-effective route that involves simple blending of NiO, MnO, Co3O4 and Li2CO3 which yields single-crystalline LiNi0.83Co0.11Mn0.06O2 with 2–3 μm particle size and good structural quality. It is shown by in situ XRD during synthesis that—while the reaction suffers from slow kinetics—the elevated temperature and longer reaction time, which are in any case required for the crystal growth, are sufficient to also complete the reaction. Furthermore, it is shown that this material is structurally and electrochemically equivalent to the material commonly synthesized from hydroxide-based precursors.