devices and electric vehicles. [1][2][3][4] To achieve even higher energy densities, the use of lithium metal as the negative electrode is considered the next big step. However, the continuous electrolyte decomposition at the electrode|electrolyte interface, owing to the lack of a stable solid electrolyte interphase (SEI), results in low Coulombic efficiency (CE) and, potentially, dendritic lithium deposition. Thus eventually cause rapid cell failure and, in a worst case, accidental short-circuiting, posing severe safety issues and hindering commercialization. [5][6][7] Nonetheless, there has been a revitalized interest in lithiummetal anodes, encouraged by recent advances towards the stabilization of the anode|electrolyte interface. These advances were achieved by different strategies, including the formulation of beneficial electrolyte compositions, [8] the application of artificial interphases, [9] the use of 3D host matrices, [10] and the replacement of conventional liquid electrolytes by solidstate electrolytes. [11] Among these strategies, the utilization of solid-state electrolytes -inorganic and/or polymeric -potentially provides great advantages concerning the safe operation of lithium-metal anodes. [12,13] The first report on polymer electrolytes, characterized by high flexibility and light weight, dated back to the late 1970s with poly(ethylene oxide) (PEO) serving as the lithium salt dissolving medium. [14,15] Later, gel-type polymer electrolytes were developed by swelling a polymer matrix, such as poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polyacrylonitrile (PAN), or poly(vinyl alcohol) (PVA) with a lithium salt-containing liquid electrolyte. [16] In such systems, the polymer essentially takes over the role of the separator and is not actively involved in the charge transport. Differently, the lithium salt anions substantially contribute to the charge transport, resulting in a lithium transference number (t Li + ) well below 0.5. This leads to a large concentration gradient and reversed electric field in the cell, which in turn results in large overpotentials, limited dis-/charge rates, and fast dendrite growth. [17][18][19][20] Accordingly, increasing the t Li + , ideally to a value close to unity, provides a solution to overcome the above mentioned challenges. The most straightforward approach to realize this is the covalent tethering of the anionic function to the polymer to immobilize the negative charge, yielding single-ion Single-ion conducting polymer electrolytes are considered particularly attractive for realizing high-performance solid-state lithium-metal batteries. Herein, a polysiloxane-based single-ion conductor (PSiO) is investigated. The synthesis is performed via a simple thiol-ene reaction, yielding flexible and self-standing polymer electrolyte membranes (PSiOM) when blended with poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). When incorporating 57 wt% of organic carbonates, these polymer membranes provide a Li + conductivity of >0.4 mS cm −1 at 20 °C ...

The electrochemical carbon dioxide reduction on copper attracted considerable attention within the last decade, since Cu is the only elemental transition metal that catalyses the formation of short-chain hydrocarbons and alcohols. Research in this field is mainly focused on understanding the reaction mechanism in terms of adsorbates and intermediates. Furthermore, dynamic changes in the micro-environment of the catalyst, i.e. local pH and $$\hbox {CO}_2$$ CO 2 concentration values, play an equivalently important role in the selectivity of product formation. In this study, we present an in operando$$^{13}\hbox {C}$$ 13 C nuclear magnetic resonance technique that enables the simultaneous measurement of pH and $$\hbox {CO}_2$$ CO 2 concentration in electrode vicinity during electroreduction. The influence of applied potential and buffer capacity of the electrolyte on the formation of formate is demonstrated. Theoretical considerations are confirmed experimentally and the importance of the interplay between catalyst and electrolyte is emphasised.

Thiophosphate solid electrolytes containing metalloid ions such as silicon or germanium show a very high lithium-ion conductivity and the potential to enable solid-state batteries (SSBs). While the lithium metal anode (LMA) is necessary to achieve specific energies competitive with liquid lithium-ion batteries (LIBs), it is also well known that most of the metalloid ions used in promising thiophosphate solid electrolytes are reduced in contact with an LMA. This reduction reaction and its products formed at the solid electrolyte|LMA interface can compromise the performance of an SSB due to impedance growth. To study the reduction of these metalloid ions and their impact more closely, we used the recently synthesized Li7SiPS8 as a member of the tetragonal Li10GeP2S12 (LGPS) family. Stripping/plating experiments and the temporal evolution of the impedance of symmetric Li|Li7SiPS8|Li transference cells show a severe increase in cell resistance. We characterize the reduction of Li7SiPS8 after lithium deposition with in situ X-ray photoelectron spectroscopy, time-of-flight secondary-ion mass spectrometry, and solid-state nuclear magnetic resonance spectroscopy. The results indicate a continuous reaction without the formation of elemental silicon. For elucidating the reaction pathways, density functional theory calculations are conducted followed by ab initio molecular dynamics simulations to study the interface evolution at finite temperature. The resulting electronic density of states confirms that no elemental silicon is formed during the decomposition. Our study reveals that Li7SiPS8 cannot be used in direct contact with the LMA, even though it is a promising candidate as both a separator and a catholyte material in SSBs.

Abstract. In operando nuclear magnetic resonance (NMR) spectroscopy is one method for the online investigation of electrochemical systems and reactions. It allows for real-time observations of the formation of products and intermediates, and it grants insights into the interactions of substrates and catalysts. An in operando NMR setup for the investigation of the electrolytic reduction of CO2 at silver electrodes has been developed. The electrolysis cell consists of a three-electrode setup using a working electrode of pristine silver, a chlorinated silver wire as the reference electrode, and a graphite counter electrode. The setup can be adjusted for the use of different electrode materials and fits inside a 5 mm NMR tube. Additionally, a shielding setup was employed to minimize noise caused by interference of external radio frequency (RF) waves with the conductive components of the setup. The electrochemical performance of the in operando electrolysis setup is compared with a standard CO2 electrolysis cell. The small cell geometry impedes the release of gaseous products, and thus it is primarily suited for current densities below 1 mA cm−2. The effect of conductive components on 13C NMR experiments was studied using a CO2-saturated solution of aqueous bicarbonate electrolyte. Despite the B0 field distortions caused by the electrodes, a proper shimming could be attained, and line widths of ca. 1 Hz were achieved. This enables investigations in the sub-Hertz range by NMR spectroscopy. High-resolution 13C NMR and relaxation time measurements proved to be sensitive to changes in the sample. It was found that the dynamics of the bicarbonate electrolyte varies not only due to interactions with the silver electrode, which leads to the formation of an electrical double layer and catalyzes the exchange reaction between CO2 and HCO3-, but also due to interactions with the electrochemical setup. This highlights the necessity of a step-by-step experiment design for a mechanistic understanding of processes occurring during electrochemical CO2 reduction.