Sodium‐ion batteries (SIBs) have attracted enormous attention in recent years due to the high abundance and low cost of sodium. However, in contrast to lithium‐ion batteries, conventional graphite is unsuitable for SIB anodes because it is much more difficult to intercolate the larger Na ions into graphite layers. Therefore, it is critical to develop new anode materials for SIBs for practical use. Here, heteroatom‐doped graphene with high doping levels and disordered structures is prepared using a simple and economical thermal process. The solvothermal‐derived graphene shows excellent performance as an anode material for SIBs. It exhibits a high reversible capacity of 380 mAh g−1 after 300 cycles at 100 mA g−1, excellent rate performance 217 mAh g−1 at 3200 mA g−1, and superior cycling performance at 2.0 A g−1 during 1000 cycles with negligible capacity fade.

Although sodium ion batteries (NIBs) have gained wide interest, their poor energy density poses a serious challenge for their practical applications. Therefore, high-energy-density cathode materials are required for NIBs to enable the utilization of a large amount of reversible Na ions. This study presents a P2-type NaCoTiO (x < 0.2) cathode with an extended potential range higher than 4.4 V to present a high specific capacity of 166 mAh g. A group of P2-type cathodes containing various amounts of Ti is prepared using a facile synthetic method. These cathodes show different behaviors of the Na/vacancy ordering. NaCoO suffers severe capacity loss at high voltages due to irreversible structure changes causing serious polarization, while the Ti-substituted cathodes have long credible cycleability as well as high energy. In particular, NaCoTiO exhibits excellent capacity retention (115 mAh g) even after 100 cycles, whereas NaCoO exhibits negligible capacity retention (<10 mAh g) at 4.5 V cutoff conditions. NaCoTiO also exhibits outstanding rate capabilities of 108 mAh g at a current density of 1000 mA g (7.4 C). Increased sodium diffusion kinetics from mitigated Na/vacancy ordering, which allows high Na utilization, are investigated to find in detail the mechanism of the improvement by combining systematic analyses comprising TEM, in situ XRD, and electrochemical methods.

A breakthrough utilizing an anionic redox reaction (O 2− /O n− ) for charge compensation has led to the development of high‐energy cathode materials in sodium‐ion batteries. However, its reaction results in a large voltage hysteresis due to the structural degradation arising from an oxygen loss. Herein, an interesting P2‐type Mn‐based compound exhibits a distinct two‐phase behavior preserving a high‐potential anionic redox (≈4.2 V vs Na + /Na) even during the subsequent cycling. Through a systematic series of experimental characterizations and theoretical calculations, the anionic redox reaction originating from O 2p‐electron and the reversible unmixing of Na‐rich and Na‐poor phases are confirmed in detail. In light of the combined study, a critical role of the anion‐redox‐induced two‐phase reaction in the positive‐negative point of view is demonstrated, suggesting a rational design principle considering the phase separation and lattice mismatch. Furthermore, these results provide an exciting approach for utilizing the high‐voltage feature in Mn‐based layered cathode materials that are charge‐compensated by an anionic redox reaction.