Surface Modification Strategies for Improving the Cycling Performance of Ni-Rich Cathode Materials – Surface Modification Strategies for Improving the Cycling Performance of Ni-Rich Cathode Materials

Ni‐rich layered lithium metal oxides are the cathode active materials of choice for high‐energy‐density Li‐ion batteries. While the high content of Ni is responsible for the excellent capacity, it is also the source of interfacial instability, limiting the material\u27s lifetime due to a variety of correlated in‐ and extrinsic factors. Hence, reconciling the opposing trends of high Ni content and long‐term cycling stability by modifying the material\u27s surface is one of the challenges in the field. Here, we review various studies on surface modification of Ni‐rich (≥ 80 %) layered cathode active materials in order to categorize current research efforts. Broadly, the three strategies of coating, surface doping and washing are discussed, each with their advantages and shortcomings. In conclusion, we highlight new directions of research that could bring Ni‐rich layered lithium metal oxide cathodes from the laboratory to the real world

Design-of-experiments-guided optimization of slurry-cast cathodes for solid-state batteries

Laboratory research into bulk-type solid-state batteries (SSBs) has been focused predominantly on powder-based, pelletized cells and has been sufficient to evaluate fundamental limitations and tailor the constituents to some degree. However, to improve experimental reliability and for commercial implementation of this technology, competitive slurry-cast electrodes are required. Here, we report on the application of an approach guided by design of experiments (DoE) to evaluate the influence of the type/content of polymer binder and conductive carbon additive on the cyclability and processability of Li$_{1+x}$(Ni$_{0.6}$Co$_{0.2}$Mn$_{0.2}$)$_{1}$−xO$_{2}$ (NCM622) cathodes in SSB cells using lithium thiophosphate solid electrolytes. The predictions are verified by charge-discharge and impedance spectroscopy measurements. Furthermore, structural changes and gas evolution are monitored via X-ray diffraction and differential electrochemical mass spectrometry, respectively, in an attempt to rationalize and support the DoE results. In summary, the optimized combination of polymer binder and conductive carbon additive leads to high electrochemical performance and good processability

Multi‐Element Surface Coating of Layered Ni‐Rich Oxide Cathode Materials and Their Long‐Term Cycling Performance in Lithium‐Ion Batteries

The energy density of layered oxide cathode materials increases with their Ni content, while the stability decreases and degradation becomes more severe. A common strategy to mitigate or prevent degradation is the application of protective coatings on the particle surfaces. In this article, a room-tem-perature, liquid-phase reaction of trimethylaluminum (TMA) and tetraethyl orthosilicate (TEOS) with adsorbed moisture on either LiNi0.85Co0.10Mn0.05O2or LiNiO2, yielding a hybrid coating that shows synergetic benefits compared to coatings from TMA and TEOS individually, is reported. The surface layer is investigated in long-term pouch full-cell studies as well as by electron micros-copy, X-ray photoelectron spectroscopy, and differential electrochemical mass spectrometry, demonstrating that it prevents degradation primarily by a fluorine-scavenging effect, and by reducing the extent of rock salt-type phase formation

Gassing Behavior of High‐Entropy Oxide Anode and Oxyfluoride Cathode Probed Using Differential Electrochemical Mass Spectrometry

Multicomponent materials may exhibit favorable Li-storage properties because of entropy stabilization. While the first examples of high-entropy oxides and oxyfluorides show good cycling performance, they suffer from various problems. Here, we report on side reactions leading to gas evolution in Li-ion cells using rock-salt (Co₀.₂Cu₀.₂Mg₀.₂Ni₀.₂Zn₀.₂)O (HEO) or Li(Co₀.₂Cu₀.₂Mg₀.₂Ni₀.₂Zn₀.₂)OF (Li(HEO)F). Differential electrochemical mass spectrometry indicates that a robust solidelectrolyte interphase layer is formed on the HEO anode, even when using an additive-free electrolyte. For the Li(HEO)F cathode, the cumulative amount of gases is found by pressure measurements to depend strongly on the upper cutoff potential used during cycling. Cells charged to 5.0 V versus Li⁺/ Li show the evolution of O₂, H₂, CO₂, CO and POF₃, with the latter species being indirectly due to lattice O₂ release as confirmed by electron energy loss spectroscopy. This result attests to the negative effect that lattice instability at high potentials has on the gassing

Gassing Behavior of High‐Entropy Oxide Anode and Oxyfluoride Cathode Probed Using Differential Electrochemical Mass Spectrometry

Multicomponent materials may exhibit favorable Li‐storage properties because of entropy stabilization. While the first examples of high‐entropy oxides and oxyfluorides show good cycling performance, they suffer from various problems. Here, we report on side reactions leading to gas evolution in Li‐ion cells using rock‐salt (Co₀.₂Cu₀.₂Mg₀.₂Ni₀.₂Zn₀.₂)O (HEO) or Li(Co₀.₂Cu₀.₂Mg₀.₂Ni₀.₂Zn₀.₂)OF (Li(HEO)F). Differential electrochemical mass spectrometry indicates that a robust solid‐electrolyte interphase layer is formed on the HEO anode, even when using an additive‐free electrolyte. For the Li(HEO)F cathode, the cumulative amount of gases is found by pressure measurements to depend strongly on the upper cutoff potential used during cycling. Cells charged to 5.0 V versus Li⁺/Li show the evolution of O₂, H₂, CO₂, CO and POF₃, with the latter species being indirectly due to lattice O₂ release as confirmed by electron energy loss spectroscopy. This result attests to the negative effect that lattice instability at high potentials has on the gassing

Design-of-experiments-guided optimization of slurry-cast cathodes for solid-state batteries

Laboratory research into bulk-type solid-state batteries (SSBs) has been focused predominantly on powder-based, pelletized cells and has been sufficient to evaluate fundamental limitations and tailor the constituents to some degree. However, to improve experimental reliability and for commercial implementation of this technology, competitive slurry-cast electrodes are required. Here, we report on the application of an approach guided by design of experiments (DoE) to evaluate the influence of the type/content of polymer binder and conductive carbon additive on the cyclability and processability of Li$_{1+x}$(Ni$_{0.6}$Co$_{0.2}$Mn$_{0.2}$)$_{1−x}$O$_2$ (NCM622) cathodes in SSB cells using lithium thiophosphate solid electrolytes. The predictions are verified by charge-discharge and impedance spectroscopy measurements. Furthermore, structural changes and gas evolution are monitored via X-ray diffraction and differential electrochemical mass spectrometry, respectively, in an attempt to rationalize and support the DoE results. In summary, the optimized combination of polymer binder and conductive carbon additive leads to high electrochemical performance and good processability