Stabilizing lattice oxygen redox in layered sodium transition metal oxide through spin singlet state.

Reversible lattice oxygen redox reactions offer the potential to enhance energy density and lower battery cathode costs. However, their widespread adoption faces obstacles like substantial voltage hysteresis and poor stability. The current research addresses these challenges by achieving a non-hysteresis, long-term stable oxygen redox reaction in the P3-type Na2/3Cu1/3Mn2/3O2. Here we show this is accomplished by forming spin singlet states during charge and discharge. Detailed analysis, including in-situ X-ray diffraction, shows highly reversible structural changes during cycling. In addition, local CuO6 Jahn-Teller distortions persist throughout, with dynamic Cu-O bond length variations. In-situ hard X-ray absorption and ex-situ soft X-ray absorption study, along with density function theory calculations, reveal two distinct charge compensation mechanisms at approximately 3.66 V and 3.99 V plateaus. Notably, we observe a Zhang-Rice-like singlet state during 3.99 V charging, offering an alternative charge compensation mechanism to stabilize the active oxygen redox reaction.

Conversion of Surface Residual Alkali to Solid Electrolyte to Enable Na-Ion Full Cells with Robust Interfaces.

The deposition of volatilized Na+ on the surface of the cathode during sintering results in the formation of surface residual alkali (NaOH/Na2 CO3 NaHCO3 ) in layered cathode materials, leading to serious interfacial reactions and performance degradation. This phenomenon is particularly evident in O3-NaNi0.4 Cu0.1 Mn0.4 Ti0.1 O2 (NCMT). In this study, a strategy is proposed to transform waste into treasure by converting residual alkali into a solid electrolyte. Mg(CH3 COO)2 and H3 PO4 are reacted with surface residual alkali to generate the solid electrolyte NaMgPO4 on the surface of NCMT, which can be labeled as NaMgPO4@NaNi0.4 Cu0.1 Mn0.4 Ti0.1 O2 -X (NMP@NCMT-X, where X indicates the different amounts of Mg2+ and PO4 3- ). NaMgPO4 acts as a special ionic conductivity channel on the surface to improve the kinetics of the electrode reactions, remarkably improving the rate capability of the modified cathode at a high current density in the half-cell. Additionally, NMP@NCMT-2 enables a reversible phase transition from the P3 to OP2 phase in the charge-discharge process above 4.2 V and achieves a high specific capacity of 157.3 mAh g-1 and outstanding capacity retention in the full cell. The strategy can effectively and reliably stabilize the interface and improve the performance of layered cathodes for Na-ion batteries (NIBs).

Screening Heteroatom Configurations for Reversible Sloping Capacity Promises High-Power Na-Ion Batteries.

Heteroatom doping has been proved to effectively enhance the sloping capacity, nevertheless, the high sloping capacity almost encounters a conflict with the disappointing initial Coulombic efficiency (ICE). Herein, we propose a heteroatom configuration screening strategy by introducing a secondary carbonization process for the phosphate-treated carbons to remove the irreversible heteroatom configurations but with the reversible ones and free radicals remaining, achieving a simultaneity between the high sloping capacity and ICE (≈250 mAh g-1 and 80 %). The Na storage mechanism was also studied based on this "slope-dominated" carbon to reveal the reason for the absence of the plateau. This work could inspire to distinguish and filter the irreversible heteroatom configurations and facilitate the future design of practical "slope-dominated" carbon anodes towards high-power Na-ion batteries.

Highly Regio- and Stereoselective Heterogeneous Hydrosilylation of Terminal Alkynes over Cobalt-Metalated Porous Organic Polymer.

A cobalt/POL-PPh3 catalyzed ( E)-selective hydrosilylation of alkynes with PhSiH3 has been developed for the synthesis of ( E)-ß-vinylsilanes with high regio- and stereoselectivity and wide functional group tolerance. It is the first report of using porous organic polymer as a recyclable regio- and stereoselective and efficient ligand in hydrosilylation reactions in which the polymer could be recycled numerous times in a continuous flow system without loss of activity and selectivity. The earth-abundant base-metal catalyst, coordinated by heterogeneous recyclable ligand, shows promise for industrial application.

Pyrazole synthesis via a cascade Sonogashira coupling/cyclization of N-propargyl sulfonylhydrazones.

An efficient approach for the preparation of pyrazoles via a Pd(ii)/Cu(i)-catalyzed Sonogashira coupling/cyclization of N-propargyl sulfonylhydrazones has been established. In this study, we firstly report the strategic use of a Sonogashira reaction to construct pyrazole rings in a one step operation. With a broad range of functional group tolerance, bioactive 3-CF3 pyrazoles can also be synthesized easily through this domino coupling/cyclization sequence.