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Cathodes in lithium‐ion batteries with anionic redox can deliver extraordinarily high specific capacities but also present many issues such as oxygen release, voltage hysteresis, and sluggish kinetics. Identifying problems and developing solutions for these materials are vital for creating high‐energy lithium‐ion batteries. Herein, the electrochemical and structural monitoring is conducted on lithium‐rich cathodes to directly probe the formation processes of larger voltage hysteresis. These results indicate that the charge‐compensation properties, structural evolution, and transition metal (TM) ions migration vary from oxidation to reduction process. This leads to huge differences in charge and discharge voltage profile. Meanwhile, the anionic redox processes display a slow kinetics process with large hysteresis (≈0.5 V), compared to fast cationic redox processes without any hysteresis. More importantly, a simple yet effective strategy has been proposed where fine‐modulating local oxygen environment by the lithium/oxygen (Li/O) ratio tunes the anionic redox chemistry. This effectively improves its electrochemical properties, including the operating voltage and kinetics. This is also verified by theoretical calculations that adjusting anionic redox chemistry by the Li/O ratio shifts the TM 3d—O 2p bands and the non‐bonding O 2p band to a lower energy level, resulting in a higher redox reaction potential.

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Hybrid capacitors, especially sodium-ion capacitors (SICs), which combine the complementary merits of high-energy batteries and high-power capacitors, have received increasing research interest and have been expected to bridge the gap between the rechargeable batteries and EDLCs. The biggest challenge for SICs is to overcome the kinetics discrepancy between the sluggish faradaic anode and the rapid nonfaradaic capacitive cathode. To boost the Na + reaction kinetics, robust and conductive Na 2 Ti 2 O 5−x nanowire arrays have been constructed as an accessible and affordable SIC anode. It is found that the utilization of oxygen vacancies (OVs) can endow Na 2 Ti 2 O 5−x high electrical conductivity, introduce intercalation pseudocapacitance, and maintain the crystal structure integrity. It exhibits high reversible discharge capacity (225 mAh g −1 at 0.5C), superior rate capability, and ultralong lifespan when utilized as self-supported and additive-free anode for SIB, remaining almost 100% capacity retention after 20 000 cycles at 25 C. When assembled as flexible hybrid SIC (4.5 cm 3 ) with rGO/AC film cathode, a high-level energy density of 70 Wh kg −1 at power density of 240 W kg −1 based on active materials can be achieved, and high volumetric energy density (15.6 Wh L −1 ) and power density (120 W L −1 ) based on the whole packge volume can be delivered with superior cycle stability (5000 cycles, 82.5%).

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High voltage spinel LiNi 0.5 Mn 1.5 O 4 has been synthesized by an ethanol-assisted hydrothermal method.LiNi 0.5 Mn 1.5 O 4 has also been synthesized by a precipitation method and hydrothermal method for comparison. The materials were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical tests. The ethanol-assisted hydrothermal process improves the dispersity and decreases the size of particles in the presence of ethanol. With small size particles, LiNi 0.5 Mn 1.5 O 4 has an excellent rate capability. Its discharge capacity is 81.7 mA h g À1 at a high rate of 20 C. On the other hand, the ethanol-assisted hydrothermal process mixes the reagents homogeneously and improves the crystallinity. It leads to low impurities and low Mn 3+ ion content, which are beneficial for electrochemical performance. The LiNi 0.5 Mn 1.5 O 4 exhibits remarkable long-term cyclability. After 1000 cycles at a 5 C discharge rate, its discharge capacity is 102.1 mA h g À1 with a capacity retention ratio of 88.1%. It also has good high temperature performance with a capacity retention of 82.0% after 200 cycles at 55 C.