Phosphorus doping is an effective strategy to simultaneously improve the electronic conductivity and regulate the ionic diffusion kinetics of TiO2 being considered as anode materials for sodium ion batteries. However, efficient phosphorus doping at high concentration in well-crystallized TiO2 nanoparticles is still a big challenge. Herein, we propose a defect-assisted phosphorus doping strategy to selectively engineer the surface structure of TiO2 nanoparticles. The reduced TiO2–x shell layer that is rich in oxygen defects and Ti3+ species precisely triggered a high concentration of phosphorus doping (∼7.8 at. %), and consequently a TiO2@TiO2–x -P core@shell architecture was produced. Comprehensive characterizations and first-principle calculations proved that the surface-functionalized TiO2–x -P thin layer endowed the TiO2@TiO2–x -P with substantially enhanced electronic conductivity and accelerated Na ion transportation, resulting in great rate capability (167 mA h g–1 at 10 000 mA g–1) and stable cycling (99% after 5000 cycles at 10 A g–1). Combining in/ex situ X-ray diffraction with ex situ electron spin resonance clearly demonstrated the high reversibility and robust mechanical behavior of TiO2@TiO2–x -P upon long-term cycling. This work provides an interesting and effective strategy for precise heteroatoms doping to improve the electrochemical performance of nanoparticles.

The Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode has attracted great interest owing to its low cost, high capacity, and energy density. Nevertheless, rapid capacity fading is a critical problem because of direct contact of NCM811 with electrolytes and hence restrains its wide applications. To prevent the direct contact, the surface inert layer coating becomes a feasible strategy to tackle this problem. However, to achieve a homogeneous surface coating is very challenging. Considering the bonding effect between NCM811, polyvinylpyrrolidone (PVP), and polyaniline (PANI), in this work, we use PVP as an inductive agent to controllably coat a uniform conductive PANI layer on NCM811 (NCM811@PANI–PVP). The coated PANI layer not only serves as a rapid channel for electron conduction, but also prohibits direct contact of the electrode with the electrolyte to effectively hinder side reaction. NCM811@PANI–PVP thus exhibits excellent cyclability (88.7% after 100 cycles at 200 mA g–1) and great rate performance (152 mA h g–1 at 1000 mA g–1). In situ X-ray diffraction and in situ Raman are performed to investigate the charge–discharge mechanism and the cyclability of NCM811@PANI–PVP upon electrochemical reaction. This surfactant-modulated surface uniform coating strategy offers a new modification approach to stabilize Ni-rich cathode materials for lithium-ion batteries.

The migration of zinc‐ion batteries from alkaline electrolyte to neutral or mild acidic electrolyte promotes research into their flexible applications. However, discharge voltage of many reported zinc‐ion batteries is far from satisfactory. On one hand, the battery voltage is substantially restricted by the narrow voltage window of aqueous electrolytes. On the other hand, many batteries yield a low‐voltage discharge plateau or show no plateau but capacitor‐like sloping discharge profiles. This impacts the battery's practicability for flexible electronics where stable and consistent high energy is needed. Herein, an aqueous zinc hybrid battery based on a highly concentrated dual‐ion electrolyte and a hierarchically structured lithium‐ion‐intercalative LiVPO4F cathode is developed. This hybrid battery delivers a flat and high‐voltage discharge plateau of nearly 1.9 V, ranking among the highest reported values for all aqueous zinc‐based batteries. The resultant high energy density of 235.6 Wh kg−1 at a power density of 320.8 W kg−1 also outperforms most reported zinc‐based batteries. A designed solid‐state and long‐lasting hydrogel electrolyte is subsequently applied in the fabrication of a flexible battery, which can be integrated into various flexible devices as powerful energy supply. The idea of designing such a hybrid battery offers a new strategy for developing high‐voltage and high‐energy aqueous energy storage systems.

Carbon materials are most promising candidates for potassium-ion battery (PIB) anodes because of their high electrical conductivities, rational potassium storage capabilities, and low costs. However, the large volume change during the K-ion insertion/extraction and the sluggish kinetics of K-ion diffusion inhibit the development of carbon-based materials for PIBs. Here, under the guidance of density functional theory, N/P-codoped ultrafine (≤20 nm) carbon nanoparticles (NP-CNPs) with an expanded interlayer distance, improved electrical conductivity, shortened diffusion distance of K ions, and promoted adsorption capability toward K ions are synthesized through a facile solvent-free method as a high-performance anode material for PIBs. The NP-CNPs show a high capacity of 270 mA h g–1 at 0.2 A g–1, a remarkable rate capability of 157 mA h g–1 at an extremely high rate of 5.0 A g–1, and an ultralong cycle life with a high capacity of 190 mA h g–1 and a retention of 86.4% at 1.0 A g–1 after 4000 cycles. The potassium storage mechanism and low volume expansion for NP-CNPs are revealed through cyclic voltammetry, in situ Raman, and ex situ XRD. This work paves a new way to design and fabricate carbon-based nanostructures with high reversible capacity, great rate capability, and stable long-term performance.

Surface modification through Li 3 PO 4 (LPO) coating is a brilliant approach to inhibit oxygen release of Ni-rich layered Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (NCM 811 ) cathodes, particularly under highly delithiated states, which can help tackle the thermal runaway issue for industrial applications. However, the mechanism of LPO prohibiting the release of the oxygen from the surface of NCM 811 is still unclear. Herein we systematically investigate the critical role of the LPO protective layer through combining atomic-scale microscopy and in/ex situ techniques. In particular, results from electrochemical impedance spectroscopy, galvanostatic intermittent titration technique test, focused ion beam-high resolution transmission electron microscopy, and in situ X-ray diffraction, unequivocally identifies that the LPO layer can inhibit the transformation from layered-like to rock-salt-like structure. Ex situ soft X-ray absorption spectroscopy and in situ Raman further reveal the improved intensity of metal−oxide bonds with the suppression of phase transition, thus inhibiting surface oxygen release. This work provides inspiration for better understanding of surface coating on stabilizing the Ni-rich cathodes.