RESUMEN
Given the merits of abundant resource, low cost and high electrochemical activity, hard carbons have been regarded as one of the most commercializable anode material for sodium-ion batteries (SIBs). However, poor rate capability is one of the main obstacles that severely hinder its further development. In addition, the relationships between preparation method, material structure and electrochemical performance have not been clearly elaborated. Herein, a simple but effective strategy is proposed to accurately construct the multiple structural features in hard carbon via adjusting the components of precursors. Through detailed physical characterization of the hard carbons derived from different regulation steps, and further combined with in-situ Raman and galvanostatic intermittent titration technique (GITT) analysis, the network of multiple relationships between preparation method, microstructure, sodium storage behavior and electrochemical performance have been successfully established. Simultaneously, exceptional rate capability about 108.8 mAh g-1 at 8 A g-1 have been achieved from RHC sample with high reversible capacity and desirable initial Coulombic efficiency (ICE). Additionally, the practical applications can be extended to cylindrical battery with excellent cycle behaviors. Such facile approach can provide guidance for large-scale production of high-performance hard carbons and provides the possibility of building practical SIBs with high energy density and durability.
RESUMEN
Large reserves, high capacity, and low cost are the core competitiveness of disordered carbon materials as excellent anode materials for sodium-ion batteries (SIBs). And the existence and improper treatment of a large number of organic solid wastes will aggravate the burden on the environment, therefore, it is significant to transform wastes into carbon-based materials for sustainable energy utilization. Herein, a kind of hard carbon materials are reported with waste biomass-foam as the precursor, which can improve the sodium storage performance through pre-oxidation strategy. The introduction of oxygen-containing groups can promote structural cross-linking, and inhibit the melting and rearrangement of carbon structure during high-temperature carbonization that produces a disordered structure with a suitable degree of graphitization. Moreover, the micropore structure are also regulated during the high-temperature carbonization process, which is conducive to the storage of sodium ions in the low-voltage plateau region. The optimized sample as an electrode material exhibits excellent reversible specific capacity (308.0 mAh g-1) and initial Coulombic efficiency (ICE, 90.1%). In addition, a full cell with the waste foam-derived hard carbon anode and a Na3V2(PO4)3 cathode is constructed with high ICE and energy density. This work provides an effective strategy to conversion the waste to high-value hard carbon anode for sodium-ion batteries.
RESUMEN
Stocking of bigheaded carp (mainly Hypophthalmichthys nobilis and H. molitrix) is commonly used in (sub)tropical Chinese reservoirs to control phytoplankton, but with ambiguous results. Whether these carp act as a phosphorus (P) source or sink for phytoplankton is debated. We compared the trophic structures in twenty-three reservoirs with different nutrient concentrations in the flood season (after bigheaded carp introduction) with the dry season (after bigheaded carp harvesting). Fish biomass was positively related to TP, and the slope of the relationship showed no difference between seasons. Bigheaded carp harvesting exceeded the amount introduced, which may explain an observed lower intercept of the relationship and fish biomass to the TP ratio in the dry season. Fish predation pressure on zooplankton (fish: zooplankton biomass ratio as a proxy) was highest in the flood season and increased with TP in both seasons. Accordingly, zooplankton grazing effect on phytoplankton (zooplankton: phytoplankton biomass ratio as a proxy) decreased with fish biomass. Furthermore, both the zooplankton biomass and the zooplankton: phytoplankton biomass ratio were among the lowest reported in the literature for the nutrient range studied. Fish grazing effect on phytoplankton (fish: phytoplankton biomass ratio as a proxy) was also highest in the flood season and decreased with TP in both seasons. Nanoplankton was the dominant phytoplankton group in oligotrophic to mesotrophic reservoirs, while filamentous cyanobacteria dominated in eutrophic reservoirs. Chlorophyll a increased with TP and fish biomass, whereas the yield of chlorophyll a per TP (Chla: TP ratio) increased with fish biomass. Accordingly, both chlorophyll a and the Chla: TP ratio were highest in the flood season. We conclude that bigheaded carp act as P sink at the ecosystem level but as P source for phytoplankton, and enhance the yield of chlorophyll a per TP and thus eutrophication.
