Anion redox contributes to the anomalous capacity exceeding the theoretical limit of layered oxides. However, double-high activity and reversibility is challenging due to the structural rearrangement and potential oxygen loss. Here, we propose a strategy for constructing a dual honeycomb-superlattice structure in Na 2/3 [Li 1/7 Mn 5/14 ][Mg 1/7 Mn 5/14 ]O 2 to simultaneously realize high activity and reversibility of lattice O redox. Theoretical simulation and electrochemical tests show that [Li 1/7 Mn 5/14 ] superlattice units remarkably trigger the anion redox activity and enable the delivery of a record capacity of 285.9 mA g À 1 in layered sodium-ion battery cathodes. Nuclear magnetic resonance and in situ X-ray diffraction reveal that [Mg 1/7 Mn 5/14 ] superlattice units are beneficial to the structure and anion redox reversibility, where Li + reversibly shuttles between Na layers and transition-metal slabs in contrast to the absence of [Mg 1/7 Mn 5/14 ] units. Our findings underline the importance of multifunctional units and provide a path to advanced battery materials.

Although being regarded as a promising cathode candidate for Na-ion batteries, Na3V2(PO4)3 is still plagued with a congenital drawback that only a limited theoretical specific capacity of 400 Wh kg–1 can be achieved by employing two-electron reaction. This study focuses on enhancing the energy density by enabling a fourth Na+ intercalation upon discharge, which increases the theoretical specific capacity to around 494 Wh kg–1. The reaction mechanism of Na3V2(PO4)3 in the whole potential range of charge/discharge (1.0–3.8 V) is elaborately investigated by the combination of 23Na/31P solid-state nuclear magnetic resonance (NMR) and cryogenic-temperature electron paramagnetic resonance (EPR) for the first time. EPR measurement under 1.8 K manifests the generation of V2+ with rhombohedral distortion upon the fourth Na+ intercalation process of Na3V2(PO4)3. Besides, this study pinpoints the profound impact of polyanion site substitution to the local structural transformation of Na3V2(PO4)3 upon Na+ (de)­intercalation, which corroborates that the boron substitution into phosphorus site can broaden the range of solid–solution reaction, accelerate the structural transition toward V2+-containing phase, and refrain the short scale heterogeneity of P and Na nuclei.

Lithium‐excess manganese layered oxide Li2MnO3, attracts much attention as a cathode in Li‐ion batteries, due to the low cost and the ultrahigh theoretical capacity (≈460 mA h g−1). However, it delivers a low reversible practical capacity (<200 mA h g−1) due to the irreversible oxygen redox at high potentials (>4.5 V). Herein, heavy fluorination (9.5%) is successfully implemented in the layered anionic framework of a Li–Mn–O–F (LMOF) cathode through a unique ion‐exchange route. F substitution with O stabilizes the layered anionic framework, completely inhibits the O2 evolution during the first cycle, and greatly enhances the reversibility of oxygen redox, delivering an ultrahigh reversible capacity of 389 mA h g−1, which is 85% of the theoretical capacity of Li2MnO3. Moreover, it also induces a thin spinel shell coherently forming on the particle surface, which greatly improves the surface structure stability, making LMOF exhibit a superior cycling stability (a capacity retention of 91.8% after 120 cycles at 50 mA g−1) and excellent rate capability. These findings stress the importance of stabilizing the anionic framework in developing high‐performance low‐cost cathodes for next‐generation Li‐ion batteries.

The microscopic chemical environment of Na in Na 3 V 2 (PO 4 ) 3 was observed and analyzed using solid-state nuclear magnetic resonance. The results demonstrated that Na in the two chemical environments in Na 3 V 2 (PO 4 ) 3 corresponded to the signal peaks between 80 and 16 ppm in the 23 Na NMR spectrum. The peak at around −11 ppm was assigned to impurities, possibly containing sodium carbonate. On basis of the new assignment, the 23 Na spectra of Na 3 V 2 (PO 4 ) 3 under different charging and discharging conditions were investigated and well explained.

The extreme fast charging (XFC) capability of graphite anodes is becoming increasingly important with the development of electric vehicles due to the usage and safety requirement. In this work, the XFC performance of the graphite anodes is improved by simply adding fluoroethylene carbonate (FEC) into the electrolyte. This robust system is studied by in situ nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to unravel the kinetic mechanism. The Li local environments in the graphite are detected by in situ NMR, which reveals the phase transitions during XFC without and with the FEC additive and the corresponding Li-ion mobility. The graphite conductivity variation is estimated by in situ EPR, and the plated Li can be clearly observed in the later period of XFC. The kinetics of graphite lithiation is deduced to be surface-controlled during the dilute stages and bulk-controlled during the dense stages. The solid electrolyte interphase (SEI) formed with FEC is more homogeneous and richer in LiF, which delivers a faster Li+ transport ability and results in the improvement of the surface kinetics. The major advantage of FEC additive is in the optimization of the Li plating behavior. Without FEC, the Li deposits grow locally, while the FEC additive consumes more currents to form the SEI and facilitate the uniform deposition of metallic Li on graphite during XFC. These results display the versatility of in situ NMR and EPR technologies in the research of XFC kinetics.