Sulfur/carbon composites are promising next generation cathode materials for high energy density lithium batteries and thus, their discharge and charge properties have been studied with increasing intensity in recent years. While the sulfur-based redox reactions are reasonably well understood, the knowledge of deleterious side reactions in lithium-sulfur batteries is still limited. In particular, the gassing behavior has not yet been investigated, although it is known that lithium metal readily reacts with the commonly used ethereal electrolytes. Herein, we describe, for the first time, gas evolution in operating lithium-sulfur cells with diglyme-based electrolyte and evaluate the effect of the polysulfide shuttle-suppressing additive LiNO 3 . Using the combination of two operando techniques (pressure measurements and online continuous flow differential electrochemical mass spectrometry coupled with infrared spectroscopy) demonstrates that the additive dramatically reduces, but does not completely eliminate gassing. The major increase in pressure occurs during charge, immediately after fresh lithium is deposited, but there are differences in gas generation during cycling dependent on the addition of LiNO 3 . Cells with LiNO 3 show evolution of N 2 and N 2 O in addition to CH 4 and H 2 , the latter being the main volatile decomposition products. Collectively, these results provide novel insight into the important function of LiNO 3 as a stabilizing additive in lithium-sulfur batteries.J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-7 | 1

Because of their exceptionally high specific energy, aprotic lithium oxygen (Li-O2) batteries are considered as potential future energy stores. Their practical application is, however, still hindered by the high charging overvoltages and detrimental side reactions. Recently, the use of redox mediators dissolved in the electrolyte emerged as a promising tool to enable charging at moderate voltages. The presented work advances this concept and distinctly improves capacity and cycling stability of Li-O2 batteries by combining high redox mediator concentrations with a solid electrolyte (SE). The use of high redox mediator concentrations significantly increases the discharge capacity by including the oxidation and reduction of the redox mediator into charge cycling. Highly efficient cycling is achieved by protecting the lithium anode with a solid electrolyte, which completely inhibits unfavored deactivation of oxidized species at the anode. Surprisingly, the SE also suppresses detrimental side reactions at the carbon electrode to a large extent and enables stable charging completely below 4.0 V over a prolonged period. It is demonstrated that anode and cathode communicate deleteriously via the liquid electrolyte, which induces degradation reactions at the carbon electrode. The separation of cathode and anode with a SE is therefore considered as a key step toward stable Li-O2 batteries, in conjunction with a concentrated redox mediator electrolyte.

The cycling performance and in operando gas analysis of LiNi0.5Mn1.5O4 (LNMO)/graphite cells with reasonably high loading, containing a "standard" carbonate-based electrolyte is reported. The gas evolution over the first couple of cycles was thoroughly investigated via differential electrochemical mass spectrometry (DEMS), neutron imaging and pressure measurements. The main oxidation and reduction products were identified as CO2, H2 and C2H4. In different sets of experiments graphite was substituted with delithiated LiFePO4 (LFP) and LNMO with LFP to distinguish between processes occurring at either anode or cathode and gain mechanistic insights. Both C2H4 and H2 were found to be mainly formed at the anode side, while CO2 is generated at the cathode. The results from DEMS analysis further suggest that the Ni redox couples play a profound role in the evolution of CO2 at the LNMO/electrolyte interface. Lastly, it is shown that the cycling stability and capacity retention of LNMO/graphite cells can be considerably improved by a simple cell formation procedure.

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We describe the benefits of an online continuous flow differential electrochemical mass spectrometry (DEMS) method that allows for realistic battery cycling conditions. We provide a detailed description on the buildup and the role of the different components in the system. Special emphasis is given on the cell design. The retention time and response characteristics of the system are tested with the electrolysis of Li2O2. Finally, we show a practical application in which a Li-ion battery is examined. The value of long-term DEMS measurements for the proper evaluation of electrolyte decomposition is demonstrated by an experiment where a Li(1+x)Ni(0.5)Mn(0.3)Co(0.2)O2 (NMC 532)/graphite cell is cycled over 20 charge/discharge cycles.

The use of functionalized electrolytes is effective in mitigating the poor cycling stability of silicon (Si), which has long hindered the implementation of this promising high-capacity anode material in next-generation lithium-ion batteries. In this Letter, we present a comparative study of gaseous byproducts formed by decomposition of fluoroethylene carbonate (FEC)containing and FEC-free electrolytes using differential electrochemical mass spectrometry and infrared spectroscopy, combined with long-term cycling data of half-cells (Si vs Li). The evolving gaseous species depend strongly on the type of electrolyte; the main products for the FEC-based electrolyte are H 2 and CO 2 , while the FEC-free electrolyte shows predominantly H 2 , C 2 H 4 , and CO. The characteristic shape of the evolution patterns suggests different reactivities of the various Li x Si alloys, depending on the cell potential. The data acquired for long-term cycling confirm the benefit of using FEC as cosolvent in the electrolyte.

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Simultaneous acquisition of electrochemical impedance spectroscopy and quartz crystal microbalance (EIS-EQCM) data in cyclic electrode potential scans was used to characterize nonstationary underpotential deposition (UPD) of atomic layers of Ag on Au and Cu on Pt. Both EIS and EQCM data sets complemented each other in the elucidation of interface models and the investigation of different aspects of the interfacial dynamics. EIS-EQCM provided an opportunity to monitor coadsorption and competitive adsorption of anions during the Ag and Cu UPD using (i) the electrode mass change, (ii) adsorption capacitances, and (iii) double-layer capacitances. Kinetic information is available in the EIS-EQCM through the charge transfer resistances and apparent rate coefficients. The latter expresses the rate of UPD into the partially covered electrode surface. The apparent rate coefficients for the Ag UPD were determined to vary from 0.15 to 0.45 cm/s which is between the standard constant rates k 0 of Ag bulk deposition on Ag reported previously for different Ag surfaces. Cu UPD on Pt and Ag UPD on Au contributed differently into a resonance resistance ΔR(E) available from the EQCM data sets. Spontaneous surface alloying between Ag and Au during the Ag UPD continuously increased the ΔR, while the Cu overlayer formation on Pt as well as experiments without Ag þ and Cu 2þ in the solution did not change this parameter significantly. The EIS-EQCM appeared to be a promising tool for an improved characterization and understanding of nonstationary electrochemical interfaces.