Electrochemical performance of the layered compound CrPS 4 for the usage as anode material in sodium-ion batteries (SIBs) was examined and exceptional reversible long-term capacity and capacity retention were found. After 300 cycles, an extraordinary reversible capacity of 687 mAh g −1 at a current rate of 1 A g −1 was achieved, while rate capability tests showed an excellent capacity retention of 100%. Detailed evaluation of the data evidence a change of the electrochemical reaction upon cycling leading to the striking long-term performance. Further investigations targeted the reaction mechanism of the first cycle by applying complementary techniques, i.e., powder X-ray diffraction (XRD), pair distribution function (PDF) analysis, X-ray absorption spectroscopy (XAS), and 23 Na/ 31 P magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The results indicated an unexpectedly complex reaction pathway including formation of several intercalation compounds, depending on the amount of Na inserted at the early discharge states and subsequent conversion to Na 2 S and strongly disordered metallic Cr at the completely discharged state. While XAS measurements suggest no further presence of intermediates after formation of Na intercalation compounds, several different phases are detected via MAS NMR upon continued discharging. Especially the data obtained from the MAS NMR investigations therefore point toward a very complex reaction pathway. Furthermore, solid electrolyte interphase (SEI) formation, resulting in the presence of NaF, was observed. After recharging the anode material, no structural longrange order occurred, but short-range order indeed resembled the local environment of the starting material, to a certain extent.

The layered hypothiophosphate CuCrP2S6 was identified as promising candidate for the application as anode in sodium‐ion batteries exhibiting an appropriate electrochemical performance (409 mAh g−1 after 200 cycles @ 1 A g−1). The electrochemical long‐term experiments suggest that the reaction mechanism changed upon repeated discharging and charging. The initial discharge and charge process was studied by X‐ray diffraction evidencing that at the early discharge stages, Na+ was intercalated into the interlayer space accompanied by a simultaneous reduction of Cu+ to metallic Cu, which was extruded from the host. At later stages of discharge, a conversion of the intermediate phase to Cu0, amorphous Cr0 and P0 embedded in nanocrystalline Na2S occurred. After recharging, only reflections of nanocrystalline NaF could be identified, which is part of the generated solid electrolyte interphase (SEI) layer. In contrast to observation made in literature, elemental Cu seems to be oxidized during the charge process again.

The Cover Feature illustrates the combined sodium intercalation and copper extrusion mechanism occurring during the discharge process of CuCrP2S6 anodes in sodium‐ion batteries. Initially, Na+ ions intercalate into the van der Waals gaps of CuCrP2S6 and Cu+ ions are expelled followed by reduction to elemental Cu. During this initial process the crystallinity of the host structure is mainly maintained, but an expansion of the interlayer space is observed. More information can be found in the Research Article by J. van Dinter et al.