Single-ion conducting polymer electrolytes are considered ideal for suppressing dendritic lithium deposition, but so far suffered instability at elevated potentials and, thus, incompatibility with nextgeneration high-energy cathodes such as Ni-rich LiNi1-x-yCoxMny]O2 (NCM(1-x-y)xy).Herein, we show that the thoughtful design of electrolytes based on multi-block copoly(arylene ether sulfone)s and incorporating suitable "molecular transporters" (such as propylene carbonate) may, in fact, enable the realization of high-energy lithium-metal batteries employing, for the first time, NCM811-based positive electrodes. These batteries can be cycled with high reversible capacity at various temperatures, including 20 °C and even 0 °C, for more than 500 cycles without substantial capacity fading when applying an optimized charging mode. The careful electrochemical characterization and ex situ investigation of the electrode/electrolyte interfaces reveals, moreover, that the use of such single-ion conductor successfully inhibits dendritic lithium metal deposition, while particular care has to be taken for the interface between the electrolyte and the NCM811 cathode.

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.

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The presence of fluorine, especially in the electrolyte, frequently has a beneficial effect on the performance of lithium batteries owing to, for instance, the stabilization of the interfaces and interphases with the positive and negative electrode. However, the presence of fluorine is also associated with reduced recyclability and low biodegradability. Herein, we present a single-ion conducting multi-block copolymer electrolyte comprising a fluorine-free backbone and compare it with the fluorinated analogue reported earlier. Following a comprehensive physicochemical and electrochemical characterization of the copolymer with the fluorine-free backbone, the focus of the comparison with the fluorinated analogue was particularly on the electrochemical stability towards oxidation and reduction as well as the reactions occurring at the interface with the lithium-metal electrode. To deconvolute the impact of the fluorine in the ionic side chain and the copolymer backbone, suitable model compounds were identified and studied experimentally and theoretically. The results show that the absence of fluorine in the backbone has little impact on the basic electrochemical properties such as the ionic conductivity, but severely affects the electrochemical stability and interfacial stability. The results highlight the need for a very careful design of the whole polymer for each desired application -essentially, just like for liquid electrolytes. ASSOCIATED CONTENTSupporting Information. Synthesis procedures, NMR spectra, membrane preparation, characterization methods, details on the DFT simulation, GPC results, overpotential inset, and SAXS pattern. This material is available free of charge via the Internet at http://pubs.acs.org.