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In this work, nitrogen-doped carbon-coated NaV 3 O 8 (NVO@NC) were successfully synthesized by a simple rheological phase method using melamine as a nitrogen source. X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM) analyses revealed that nitrogen-doped carbon-coated didn't change the crystal structure of NVO but altered the thickness and properties of the surface coating. Among obtained composites, NVO@NC containing a molar ratio of melamine to citric acid of 2.75:1.25 displayed the best electrochemical properties. The electrochemical tests suggested discharge capacity reaching 231.3 mAh g−1 at 150 mA g−1, with discharge capacity remaining at 169.4 mAh g−1 after 100 cycles. Electrochemical impedance spectroscopy (EIS) proved that the coated materials delivered a much lower resistance than that of bulk NVO. Galvanostatic intermittent titration technique (GITT) tests demonstrated sodium ion diffusion coefficient was greatly enhanced after nitrogen-doped carbon coating. In conclusion, nitrogen-doped carbon might increase material conductivity, aid in the formation of SEI films on electrode surfaces, and improve electrode material stability, resulting in NVO materials with high-capacity and ultrafast Na-ion storage. [ABSTRACT FROM AUTHOR]

Sodium titanate (Na 2 Ti 6 O 13) exhibits great potential as a sodium-ion batteries (SIBs) anode material, nevertheless the limited electronic conductivity markedly hampers its applications. To combat this shortcoming, carbon coating has been widely employed to fabricate Na 2 Ti 6 O 13 /C composites; however, this method requires a high-temperature processing that is energy-intensive releases environmental pollutants. Herein, silver is used as a novel conducting agent, and we demonstrated a simple and efficient method to prepare Ag@Na 2 Ti 6 O 13 composites. We find that nano-sized silver particles (3%) are well distributed on the Na 2 Ti 6 O 13 surface, leading to boosted conductivity of the composites. As a result, the Ag@Na 2 Ti 6 O 13 electrode exhibits an excellent performance for Na+ insertion, where after 100 cycles a discharge capacity of 189 mAh g −1 is achieved, demonstrating superior capacity retention of 97.9%. The result of silver coating on the battery performance was investigated coherently by various techniques, such as electrochemical impedance spectroscopy. Our work provides a feasible approach to prepare electronically conductive compounds for battery applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na 2 THBQ were combined with CDs as cathode materials in SIBs for the first time. • o -Na 2 THBQ/CDs-2 performed good cycling stability and rate performance. • The mechanism of o -Na 2 THBQ/CDs-2 was explored by ex-situ tests. • The sodium ion diffusion coefficient of the materials was tested by GITT. Organic compounds are considered auspicious due to their widespread presence in nature, low cost, and sustainability. However, the inherent drawbacks of these organics' compounds, like low-conductivity and high-solubility, restrict their large-scale application. To solve these problems, we innovatively combined carbon quantum dots (CDs) with active substances (tetrahydroxybenzoquinone ortho -disodium salt (o -Na 2 THBQ)) at different mass ratios. The optimized o -Na 2 THBQ/CDs-2 (the mass ratio of o -Na 2 THBQ to CDs is 10:2) exhibited excellent electrochemical performance, the first-cycle discharge specific capacity was 410 mAh g−1 and maintained 182 mAh g−1 after 500 cycles, and the Coulombic efficiency was nearly 100 %. After 1300 cycles, the o -Na 2 THBQ/CDs-2 composite demonstrated a high specific capacity of 63 mAh g−1 at 500 mA g−1. This work provides a reference to design an optimal composite ratio of carbon dots (CDs) and organics to fabricate cathode materials for high-performance sodium-ion batteries. [ABSTRACT FROM AUTHOR]

• NVO material doped by niobium ion (Nb5+) was successfully prepared by the rheological phase method. • Nb-doping lead to an expansion of the lattice volume and increase the intrinsic conductivity. • NaNb 0.018 V 2.982 O 8 demonstrates high-rate capability and long-term cyclability. • Pseudocapacitive behavior of Nb-doped NVO is confirmed by kinetics analysis. In this work, NaNb 0.018 V 2.982 O 8 (NVO-0.018Nb) composite was served as the cathode of sodium-ion batteries (SIBs) to deliver a superior Na-storage capacity of 187 mA h g−1 at the current density of 1 C and voltage range of 1.5–4.0 V, and favorable energy density (419.3 Wh kg−1). Electrochemical impedance spectroscopy (EIS) measurements displayed decreased charge transfer resistance in the NVO-0.018Nb composite. The detailed kinetic analysis revealed enhanced surface-controlled behaviors, leading to improved sodium-storage capability. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analyses demonstrated that NVO-0.018Nb composite exhibited unique structure with significantly enhanced structural stability during fast cycling. In sum, the proposed method looks promising for the design of future advanced electrode materials of SIBs. [ABSTRACT FROM AUTHOR]

Conjugated carbonyl compounds with high theoretical capacity, low cost, structural flexibility and abundant resources are potential cathodes in metal-ion batteries (lithium-LIBs, sodium-SIBs, kalium-KIBs). Regrettably, their inherent drawbacks of high solubility and low electrical conductivity limit their further application. Herein, different mass ratios of reduced graphene oxide wrapped poly (1,5-anthraquinonyl sulfide) (PAQS/rGO) composites were prepared through a calcination-treatment process aiming at decreasing the dissolution and enhancing the conductivity. XRD, FTIR and Raman analysis confirmed the successful synthesis of PAQS. XRD analysis also confirmed the conversion of GO to rGO. Four-probe test results showed that the conductivity of composites increased as the rGO ratio increased. SEM images showed that PAQS/rGO composites presented microsphere morphologies. Profiting from the enhanced conductivity and limited dissolution in electrolyte, the PAQS2 (the mass ratios of PAQS and rGO is 10:2) composite exhibited outstanding performance both in half- and full-batteries. In LIBs/SIBs, PAQS2 exhibited reservable discharge capacities of 121 and 115 mAh g−1 at 50 mA g−1 after 200 and 400 cycles, respectively. In PTPAn/PAQS2 all-organic Li/Na-ion batteries, reservable charge/discharge capacities of 42.1/39 and 42.1/40.4 mAh g−1 were retained at 50 mA g−1 after 200 cycles, respectively. Ex-situ FT-IR analysis further performed the redox reaction of carbonyl groups during charging and discharging. [ABSTRACT FROM AUTHOR]

The impacts of Cu substitution upon the cycling stability of Na x MO 2 (M = Fe, Mn) cathodes are systematically studied. Evidenced by CuO segregation and XPS analysis, the average valence of Mn can hardly reach +4, possibly owing to the production of Mn(II). It is proposed that, Cu substitution can efficiently enhance the cycling stability by reducing the content of Mn(III) and suppressing the electrochemical activities of Mn4+/3+ redox couple. • Cycling stability of Na x MO 2 (M = Cu, Fe, Mn) cathodes are systematically studied. • CuO segregation is evidenced to be associated with the limited valent state of Mn. • Adding Cu2+ actually lower Mn valence by decreasing Mn(III) and generating Mn(II). • Cu2+-substitution may enhance the cycling stability mainly by suppressing Mn(III). Adding Cu2+ has substantially boosted the practical potentiality of Fe/Mn-based layered cathodes for sodium ion batteries (SIBs) owing to the enhanced stabilities, which were previously ascribed to the raised valence of Mn. Herein, the roles of Cu2+ are verified by investigating Cu2+-substituted materials with the stoichiometry of Na 0.5+x Cu x Fe 0.5-x Mn(IV) 0.5 O 2. Surprisingly, it is found that Mn valence can hardly reach the expected value (IV) even by adjusting Cu2+ content. For the first time, the separation of CuO, which has been previously detected but rarely explained, is ascribed to the restrained chemical states of Mn. Detailed analyses show that, Mn(II) is generated while Mn(III) is decreased in pace of Cu2+ substitution, actually lowering down the oxidation states of Mn. Moreover, Mn4+/3+ redox can be efficiently restricted by importing Cu2+. Albeit the loss of capacity, the cycling stability is greatly enhanced, achieving a high capacity retention of 92.3% after 200 cycles within 4.2–2.5 V. Therefore, the suppression of Jahn-Teller Mn(III) should be intrinsically responsible for the superior cycling stability after Cu2+ substitution. These findings may present a new sight to probe the roles of Cu in layered Na x MO 2 system for the design of advanced cathodes for SIBs. [ABSTRACT FROM AUTHOR]