![]() Hereby, the effect of the degree of delithiation on the discharge capacity and on the particle integrity (tracked via its surface area) was examined, both for poly- and single-crystalline NCMs. In electrochemical cycling experiments, the NCM capacitance was tracked in situ by impedance spectroscopy (EIS) using a micro-reference electrode while the upper cutoff potential was increased every third cycle stepwise from 3.9 V to 5.0 V. First, the onset of the release of lattice oxygen was identified by on-line electrochemical mass spectrometry (OEMS). To understand the impact of this instability, the correlation of oxygen release, capacity fading, and particle cracking was investigated as a function of state of charge for three nickel-rich NCMs, differing either in composition (i.e., in transition metal ratio) or in morphology (i.e., in primary crystallite size). However, the available capacity is limited due to their structural instability at high state of charge, causing the formation of a resistive surface layer upon release of lattice oxygen, observed at different upper cutoff potentials depending on the NCM composition. Nickel-rich NCMs (LiMO 2, with M = Ni, Co, and Mn) are increasingly commercialized as cathode active materials for lithium-ion batteries due to their high specific capacity. This study shows how important the chemical stability toward singlet oxygen is for today’s battery systems and that a trade-off will have to be found between chemical and electrochemical stability of the solvent to be used. Hydrogen peroxide is detrimental for cycling of a battery, as for all known cathode materials the potential where singlet oxygen is released is found to be already high enough to electrochemically oxidize hydrogen peroxide, forming protons and/or water which both react with the typi-cally used LiPF6 salt to HF that then leads to transition metal dissolution from the cathode active materials. In contrast to EC, simulations suggested DMC to be stable in the presence of singlet oxygen, which was also confirmed experimentally. In the case of EC, hydrogen peroxide and vinylene carbonate (VC) are found to be the products of the first reaction step of EC with singlet oxygen in the reac-tion cascade of the EC chemical decomposition. Ab initio calculations and on-the-fly simulations reveal a possible reaction mechanism, confirming the experimental findings. On-line gassing analysis of the decomposition of ethylene car-bonate (EC) and dimethyl carbonate (DMC) reveals different stability toward the chemical attack of singlet oxygen, which is produced in-situ by photo-excitation of the Rose bengal dye. ![]() Here we study the reactivity of chemically produced singlet oxygen with the commonly used cy-clic and linear carbonate solvents for LIB electrolytes. ![]() ![]() High degrees of delithiation of layered transition metal oxide cathode active materials (NCMs and HE NCM) for lithi-um-ion batteries (LIBs) was shown to lead to the release of singlet oxygen, which is accompanied by enhanced electro-lyte decomposition. ![]()
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