Developing new electrode materials and/or electrolytes for lithium‐ion batteries requires reliable electrochemical testing thereof. For this purpose, in academic research typically hand‐made coin‐type cells are assembled. Their advantage is a rather cheap and facile assembly, and possibility to prepare full‐cells as well as half‐cells, meaning cathode‐anode or electrode‐elemental lithium configurations. Critical parameters for testing data quality and the potential and limitations of cell tests in half‐cell configuration are discussed. Further, on the basis of a round robin test, using highly homogenous commercial electrodes, where graphite is used as anode and LiNi_0.33Mn_0.33Co_0.33O₂ (NMC111) as the cathode material, it is shown that data acquired is highly influenced by assembling parameters. Besides known variables such as the amount of electrolyte or electrode positioning, the proper height of the cell stack and the steel grade of the housing material are identified as decisive variables. Finally, it is demonstrated that under proper conditions coin cells can show a great cycle stability of >2200 cycles using 1 C as dis‐/charge rate while retaining a capacity of 80 %. This performance is close to pouch‐type cells containing the same electrodes and electrolyte, which were used as a benchmark system and showed >3500 cycles of lifetime.

In this empirical study, five electrolyte additives, namely, lithium bis(oxalato) borate, lithium difluoro(oxalato) borate, 1‐vinyl‐1,2,4‐triazole, 1‐vinyl imidazole and dimethyl‐2,5‐dioxahexane dioate are described and compared regarding their effect in LNMO//graphite cells. The additives were selected from a preliminary study of 59 potential additives. The basis electrolyte mixture is DMC/EC+1 M LiPF₆ (LP30) for all cells. All additives are able to enhance the cycle life at room temperature and at elevated temperatures (50 °C) significantly compared to the non‐additive electrolyte blend (basis electrolyte). The cell enhancement is discussed based on the solid‐electrolyte interface (SEI) and metal‐ion content on anode side. The aim of the study is to suggest promising already known as well as new additives that are able to overcome the issue of rapid capacity fading of LNMO‐based cells when the cells are cycled up to 4.8–5.0 V vs. Li/Li⁺, especially at higher temperatures.

Temperature dependent viscosity, conductivity, and density data of binary mixtures containing ethylene carbonate (EC) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)azanide (EMIM-TFSA) were determined at atmospheric pressure in a wide temperature range of (20 to 120) °C. Additionally, differential scanning calorimetry (DSC) measurements were performed from (−120 to +100) °C to characterize phase behavior of the mixtures. On the basis of the experimental data it is demonstrated that the lattice hole theory can be applied excellently to the conductivity data of the binary mixture EMIM-TFSA/EC. The viscosity data were fitted according to the Vogel–Fulcher–Tammann–Hesse (VFTH) equation and analyzed with the help of the fractional Walden rule. It is concluded that the mixtures can be classified as fragile according to ionicity. The aim of the study is to present fundamental physicochemical data about the mixtures as a basis for structure–property relationship-calculations of solvent mixtures or use as electrolytes for various applications.

Knowledge about capacity losses related to the solid electrolyte interphase (SEI) in sodium‐ion batteries (SIBs) is still limited. One major challenge in SIBs is that the solubility of SEI species in liquid electrolytes is comparatively higher than the corresponding species formed in Li‐ion batteries. This study sheds new light on the associated capacity losses due to initial SEI formation, SEI dissolution and subsequent SEI reformation, charge leakage via SEI and subsequent SEI growth, and diffusion‐controlled sodium trapping in electrode particles. By using a variety of electrochemical cycling protocols, synchrotron‐based X‐ray photoelectron spectroscopy (XPS), gas chromatography coupled with mass spectrometry (GC‐MS), and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy, capacity losses due to changes in the SEI layer during different open circuit pause times are investigated in nine different electrolyte solutions. It is shown that the amount of capacity lost depends on the interplay between the electrolyte chemistry and the thickness and stability of the SEI layer. The highest capacity loss is measured in NaPF₆ in ethylene carboante mixed with diethylene carbonate electrolyte (i.e., 5 µAh h^−1/2_pause or 2.78 mAh g·h^−1/2_pause) while the lowest value is found in NaTFSI in ethylene carbonate mixed with dimethoxyethance electrolyte (i.e., 1.3 µAh h^−1/2_pause or 0.72 mAh g·h^−1/2_pause).

Sodium‐ion batteries are becoming an increasingly important complement to lithium‐ion batteries. However, while extensive knowledge on the preparation of Li‐ion batteries with excellent cycling behavior exists, studies on applicable long‐lasting sodium‐ion batteries are still limited. Therefore, this study focuses on the cycling stability of batteries composed of Na₃V₂(PO₄)₃/C based cathodes and hard carbon anodes. It is shown that full‐cells with a decent stability are obtained for ethylene carbonate/propylene carbonate electrolyte and the conducting salt NaPF₆. With cathode loadings of 1.2 mAh/cm², after cell formation discharge capacities up to 92.6 mAh/g are obtained, and capacity retentions >90 % over 1000 charge/discharge cycles at 0.5 C/0.5 C are observed. It is shown that both, the additive fluoroethylene carbonate and impurities in the electrolyte, negatively affect the overall discharge capacity and cycling stability and should therefore be avoided. Remarkably, the internal resistances of well‐balanced and well‐built cells did not increase over 1500 cycles and 5 months of testing, which is a very promising result regarding the possible lifespan of the cells. The initial loss of active sodium ions in hard carbon remains a major problem, which can only be partially reduced by proper balancing.