Lithium solid-state batteries (Li-SSBs) require electrodes that provide a sufficiently stable interface with the solid electrolyte. Due to the often limited stability window of solid electrolytes, researchers frequently favor an InÀLi alloy instead of lithium metal as counter electrode for two-electrode measurements. Maintaining a stable potential at the counter electrode is especially important because three-electrode measurements are hard to realize in solid-state cells. Although a constant potential of about 0.6 V vs. Li + /Li is commonly accepted for the InÀLi electrode, only little is known about the behavior of this electrode. Moreover, the InÀLi phase diagram is complex containing several intermetallic phases/compounds such as the InLi phase, or line compounds such as In 4 Li 5 or In 2 Li 3 . This means that the redox potential of the InÀLi electrode depends on the alloy composition, i. e. the In/Li ratio. Here, we study the behavior of InÀLi electrodes in cells with liquid electrolyte to determine their phase evolution and several equilibrium potentials vs. Li + /Li. The room temperature equilibrium redox potential of the InÀLi electrode with the favored composition (or more precisely the Li + /(InÀInLi) electrode) is 0.62 V vs. Li + /Li. We then discuss the use of InÀLi electrodes in solid state cells using Li 3 PS 4 as solid electrolyte and give examples on the importance of the right In/Li ratio of the electrode. While the right In/Li ratio enables stable lithium insertion/deinsertion in symmetrical cells for at least 100 cycles, too much lithium in the electrode leads to a drop in redox potential combined with a rapid build-up of interface resistance.

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Cobalt-and nickel-free cathode materials are desirable for developing low-cost sodium-ion batteries (SIBs). Compared to the single P-type and O-type structures, biphasic P/O structures become a topic of interest thanks to improved performance. However, the added complexity complicates the understanding of the storage mechanism and the phase behavior is still unclear, especially over consecutive cycling. Here, the properties of biphasic P2(34%)/O3(60%) Na 0.8 Li 0.2 Fe 0.2 Mn 0.6 O 2 and its behavior at different states of charge/discharge are reported on. The material is composed of single phase O3 and P2/O3 biphasic particles. Sodium occupies the alkali layers, whereas lithium predominantly (95%) is located in the transition metal layer. An initial reversible capacity of 174 mAh g-1 is delivered with a retention of 82% dominated by Fe 3+ /Fe 4+ along with contributions from oxygen and partial Mn 3+/4+ redox. Cycling leads to complex phase transitions and ion migration. The biphasic nature is nevertheless preserved, with lithium acting as the structure stabilizer.

We study the stability of several diglyme-based electrolytes in sodium|sodium and sodium|graphite cells. The electrolyte behavior for different conductive salts [sodium trifluoromethanesulfonate (NaOTf), NaPF 6 , NaClO 4 , bis-(fluorosulfonyl)imide (NaFSI), and sodium bis-(trifluoromethanesulfonyl)imide (NaTFSI)] is compared and, in some cases, considerable differences are identified. Side reactions are studied with a variety of methods, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, online electrochemical mass spectrometry, and in situ electrochemical dilatometry. For Na|Na symmetric cells as well as for Na|graphite cells, we find that NaOTf and NaPF 6 are the preferred salts followed by NaClO 4 and NaFSI, as the latter two lead to more side reactions and increasing impedance. NaTFSI shows the worst performance leading to poor Coulombic efficiency and cycle life. In this case, excessive side reactions lead also to a strong increase in electrode thickness during cycling. In a qualitative order, the suitability of the conductive salts can be ranked as follows: NaOTf ≥ NaPF 6 > NaClO 4 > NaFSI ≫ NaTFSI. Our results also explain two recent, seemingly conflicting findings on the degree of solid electrolyte interphase formation on graphite electrodes in sodium-ion batteries [

Practical aspects of the Boehm titration method are evaluated for obtaining reliable results in the quantification of oxygen-containing surface groups in a short time. Analytical criteria such as accuracy, repeatability, precision, and robustness are applied. Oxidized multi-walled carbon nanotubes (MWCNTs) are used as the model substance. Different reaction bases (NaHCO 3(aq) , Na 2 CO 3(aq) , NaOH (aq)) are applied and treatment times are studied. We also show that smaller amounts of carbon material can be reliably analyzed by using an autotitrator combined with a pH electrode. We find that indirect titration with Na 2 CO 3 results in the highest titration precision and accuracy despite the lower base strength compared with NaOH. Therefore, CO 2 impurities do not have to be removed and only 7 min is necessary for one titration. The titration error with respect to the proposed method is 0.15% of the aliquot volume. The mixing method during the carbon treatment with bases (stirring, shaking, ultrasound treatment) has no influence on the result as long as one allows a few hours for the reaction to complete. Finally, we provide a standard operating procedure for obtaining results with high precision during Boehm titration.