Reproducible long-term cycling data of Al2O3 coated LiNi0.70Co0.15Mn0.15O2 cathodes for lithium-ion batteries.

LiNixCoyMn1-x-yO2 (NCM) based cathodes for Li-ion batteries (LIBs) are of great interest due to their higher energy density and lower costs compared to conventional LiCoO2 based cathodes. However, NCM based cathodes suffer from instabilities of the cathode-electrolyte interface resulting in faster capacity fading during long-term cycling. Different NCM compositions along with different coatings have been developed to protect the interface. However, a detailed understanding why and how coatings work is still missing. Up to now, no state-of-the-art NCM or coating material have been agreed upon yet, making it difficult to benchmark the performance of the coating material. Undefined standards complicate the use of experimentally produced data for model-based studies, which are a key element in assessing the beneficial effect of coatings. In this work, we therefore describe reproducible long-term cycling data of NCM based cathodes with and without an Al2O3 based coating. The data set is provided to be used for parameter fitting and/or as training data to encourage the simulation of the performance of LIBs in model-based approaches.

Design of Ordered Mesoporous CeO2-YSZ Nanocomposite Thin Films with Mixed Ionic/Electronic Conductivity via Surface Engineering.

Mixed ionic and electronic conductors represent a technologically relevant materials system for electrochemical device applications in the field of energy storage and conversion. Here, we report about the design of mixed-conducting nanocomposites by facile surface modification using atomic layer deposition (ALD). ALD is the method of choice, as it allows coating of even complex surfaces. Thermally stable mesoporous thin films of 8 mol-% yttria-stabilized zirconia (YSZ) with different pore sizes of 17, 24, and 40 nm were prepared through an evaporation-induced self-assembly process. The free surface of the YSZ films was uniformly coated via ALD with a ceria layer of either 3 or 7 nm thickness. Electrochemical impedance spectroscopy was utilized to probe the influence of the coating on the charge-transport properties. Interestingly, the porosity is found to have no effect at all. In contrast, the thickness of the ceria surface layer plays an important role. While the nanocomposites with a 7 nm coating only show ionic conductivity, those with a 3 nm coating exhibit mixed conductivity. The results highlight the possibility of tailoring the electrical transport properties by varying the coating thickness, thereby providing innovative design principles for the next-generation electrochemical devices.

Optimized atomic layer deposition of homogeneous, conductive Al2O3 coatings for high-nickel NCM containing ready-to-use electrodes.

Atomic layer deposition (ALD) derived ultrathin conformal Al2O3 coating has been identified as an effective strategy for enhancing the electrochemical performance of Ni-rich LiNixCoyMnzO2 (NCM; 0 ≤x, y, z < 1) based cathode active materials (CAM) in Li-ion batteries. However, there is still a need to better understand the beneficial effect of ALD derived surface coatings on the performance of NCM based composite cathodes. In this work, we applied and optimized a low-temperature ALD derived Al2O3 coating on a series of Ni-rich NCM-based (NCM622, NCM71.51.5 and NCM811) ready-to-use composite cathodes and investigated the effect of coating on the surface conductivity of the electrode as well as its electrochemical performance. A highly uniform and conformal coating was successfully achieved on all three different cathode compositions under the same ALD deposition conditions. All the coated cathodes were found to exhibit an improved electrochemical performance during long-term cycling under moderate cycling conditions. The improvement in the electrochemical performance after Al2O3 coating is attributed to the suppression of parasitic side reactions between the electrode and the electrolyte during cycling. Furthermore, conductive atomic force microscopy (C-AFM) was performed on the electrode surface as a non-destructive technique to determine the difference in surface morphology and conductivity between uncoated and coated electrodes before and after cycling. C-AFM measurements on pristine cathodes before cycling allow clear separation between the conductive carbon additives and the embedded NCM secondary particles, which show an electrically insulating behavior. More importantly, the measurements reveal that the ALD-derived Al2O3 coating with an optimized thickness is thin enough to retain the original conduction properties of the coated electrodes, while thicker coating layers are insulating resulting in a worse cycling performance. After cycling, the surface conductivity of the coated electrodes is maintained, while in the case of uncoated electrodes the surface conductivity is completely suppressed confirming the formation of an insulating cathode electrolyte interface due to the parasitic side reactions. The results not only show the possibilities of C-AFM as a non-destructive evaluation of the surface properties, but also reveal that an optimized coating, which preserves the conductive properties of the electrode surface, is a crucial factor for stabilising the long-term battery performance.

Enhancing the Electrochemical Performance of LiNi0.70Co0.15Mn0.15O2 Cathodes Using a Practical Solution-Based Al2O3 Coating.

Ni-rich Li[NixCoyMn1-x-y]O2 (NCM) cathode materials have attracted great research interest owing to their high energy density and relatively low cost. However, capacity fading because of parasitic side reactions, mainly occurring at the interface with the electrolyte, still hinders widespread application in advanced Li-ion batteries (LIBs). Surface modification via coating is a feasible approach to tackle this issue. Nevertheless, achieving uniform coatings is challenging, especially when using wet chemistry methods. In this work, a protective alumina shell on NCM701515 (70% Ni) was prepared through the reaction of surface-active -OH groups with trimethylaluminum as the precursor. The coated NCM701515 shows significantly improved capacity retention over uncoated (pristine) NCM701515. Part of the reason is the lower impedance buildup during cycling due to the effective suppression of adverse side reactions and secondary particle fracture. Taken together, the solution-based coating strategy described herein offers an easy way to apply surface treatment to stabilize Ni-rich NCM cathode materials in next-generation LIBs.

Tailoring the protonic conductivity of porous yttria-stabilized zirconia thin films by surface modification.

Porous yttria-stabilized zirconia (YSZ) thin films were prepared by pulsed laser deposition to investigate the influence of specific surface area on the electronic, oxygen ion, and protonic transport properties. Electrochemical impedance spectroscopy was carried out as a function of temperature, oxygen activity and humidity of the surrounding atmosphere. At high humidity, protons on the surface of the porous YSZ thin films lead to increased conductivity, even for temperatures up to 700 °C. With increasing relative humidity, the activation energy of proton transport decreases because of changes in the transport mechanism from Grotthuss-type to vehicle-type transport. By coating the porous YSZ films with an amorphous titania (TiO2) layer of only a few nanometer thickness using atomic layer deposition, the protonic contribution to conductivity is significantly reduced. Depositing an 18 nm-thick anatase TiO2 surface layer, the protonic conductivity contribution increases again, which can be attributed to enhanced capillary condensation because of the lower pore size. Interestingly, the filling of pores is accompanied by a decrease in proton mobility. Theses results demonstrate the significant effect that the porosity and the surface properties have on the protonic transport and further provide new design principles for developing nanostructured proton-conducting oxides.