P2-type layered oxides with the general Na-deficient composition Na _x TMO₂ (x < 1, TM: transition metal) are a promising class of cathode materials for sodium-ion batteries. The open Na⁺ transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry, Na_0.67(Mn_0.55Ni_0.21Co_0.24)O₂, Na_0.67(Mn_0.45Ni_0.18Co_0.24Ti_0.1Mg_0.03)O₂ and Na_0.67(Mn_0.45Ni_0.18Co_0.18Ti_0.1Mg_0.03Al_0.04Fe_0.02)O₂ with low, medium and high configurational entropy, respectively. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V. Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications.

Cubic Li₂Fe_0.9M_0.1SO antiperovskites with M–Co²⁺, or Mn²⁺were successfully synthesized by a solid-state technique, and studied as cathode materials in Li-batteries. The influence of the Co, and Mn cation substitution of Fe in Li₂FeSO on the resulting electrochemical performance was evaluated by galvanostatic cycling, while the reaction mechanism was explored by applyingoperandoX-ray absorption and X-ray diffraction techniques using synchrotron radiation facilities. Even 10% Fe-substitution by these metals completely changes the structural behavior of the material upon Li-removal and insertion, in comparison to Li₂FeSO. The Co-substitution significantly improves cyclability of the material at high current densities in comparison to the non-substituted material, reaching a specific capacity of 250 mAh/g at 1C current density. In contrast, the Mn-substitution leads to deterioration of the electrochemical performance because of the impeded kinetics, which may be caused by the appearance of a second isostructural phase due to formation of Jahn-Teller Mn³⁺cations upon delithiation.

A tunable redox potential and electrochemical performance are realized by anionic substitution of S by Se for the Li-rich antiperovskite (Li₂Fe)SO cathode.

Electrochemical cation intercalation into 2D NiPS₃ leads either to reduction of the (P₂S₆)⁴⁻ units (Li example) or Ni cations (Na example), or causes electrochemical reduction and decomposition of EMIM cations within the van der Waals interlayers.

Layered Na_0.8Co_0.8Ti_0.2O₂ oxide crystallizes in the β-RbScO₂ structure type (P2 modification) with Co(III) and Ti(IV) cations sharing the same crystallographic site in the metal-oxygen layers. It was synthesized as a single-phase material and characterized as a cathode in Na- and Na-ion batteries. A reversible capacity of about 110 mA h g⁻¹ was obtained during cycling between 4.2 and 1.8 V vs. Na⁺/Na with a 0.1 C current density. This potential window corresponds to minor structural changes during (de)sodiation, evaluated from operando XRD analysis. This finding is in contrast to Ti-free Na_xCoO₂ materials showing a multi-step reaction mechanism, thus identifying Ti as a structure stabilizer, similar to other layered O3- and P2-Na_xCo_1−yTi_yO₂ oxides. However, charging the battery with the Na_0.8Co_0.8Ti_0.2O₂ cathode above 4.2 V results in the reversible formation of a O2-phase, while discharging below 1.5 V leads to the appearance of a second P2-layered phase with a larger unit cell, which disappears completely during subsequent battery charge. Extension of the potential window to higher or lower potentials beyond the 4.2–1.8 V range leads to a faster deterioration of the electrochemical performance. After 100 charging-discharging cycles between 4.2 and 1.8 V, the battery showed a capacity loss of about 20% in a conventional carbonate-based electrolyte. In order to improve the cycling stability, different approaches including protective coatings or layers of the cathodic and anodic surface were applied and compared with each other.