ABSTRACT
Environmentally friendly P2-type layered iron manganese oxides appear to be one of the most potential cathode materials for sodium-ion batteries (SIBs). However, their practical application is hindered by the unfavorable phase transitions, dissolution of transition metals, and poor air stability. One effective strategy by either single-cation doping or high-cost Li involved co-doping is used to alleviate the problems. Here, low-cost Cu/Ti co-doping is introduced to boost P2-Na0.7Cu0.2Fe0.2Mn0.5Ti0.1O2 as an air and electrochemical stable cathode material for SIBs. The resulting electrode delivers an initial capacity of 130 mAh g-1 at 0.1C within 2.0-4.2 V, a reversible discharge capacity of 61.0 mAh g-1 at a high rate of 5C and a capacity retention ratio exceeding 71.1% after 300 cycles. In particular, the co-doped crystal structure is well-maintained after 1 month of exposure to air, and even 3 days of soaking in water. Furthermore, the enhancement is elucidated by the effectively mitigated P2-Z and the completely suppressed P2-P'2 phase transitions, the decreased volume variation proved by in-situ X-ray diffraction (XRD), as well as the lowered transition-metal dissolution evidenced by inductively coupled plasma optical emission spectrometer (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The low-lost Cu/Ti doping strategy could thus be effective for designing and preparing environmentally friendly and high-performance cathode materials for SIBs.
ABSTRACT
Sodium ion batteries (SIBs) have recently been promising in the large-scale electric energy storage system, due to the low cost, abundant sodium resources. Mn-based layered oxide cathode materials have been widely investigated, because of the high theoretical specific capacity, low cost, and abundant reserves. However, their development is limited by the problems of Jahn-Teller distortion, Na+ /vacancy ordering, complex phase transitions, and irreversible anionic redox during cycling. Ion substitution strategy is one simple and effective way to regulate the crystal structure and boost sodium-storage performances of Mn-based cathode materials. In this review, we summarize the progress and mechanism of ion-substituted Mn-based oxides, establish a composition-crystal structure-electrochemical performance relationship, and also offer perspectives for guiding the design of high-performance Mn-based oxides for SIBs.
ABSTRACT
An experiment was conducted to examine the effects of drought and rewatering on growth and photosynthetic physioecological characteristics of Xanthoceras sorbifolia, with 2-year-old seedlings as test materials. There are three treatments, i.e., light drought stress (soil water content 14.3%-16.2%), moderate drought stress(10.6%-12.5%) and severe drought stress (6.8%-8.7%), with the control (21.8%-23.7%). The results showed that with the increases of drought stress, the dry mass per plant, height, basal diameter, leaf number, and leaf area significantly decreased, and length of the main root and the secondary root increased. The gas exchange parameters gradually decreased with the increases of drought stress. The level of Pn was caused by stomatal factors from 10:00 to 14:00 and by non-stomatal factors after 14:00. Apparent CO2 use efficiency (CUE) of X. sorbifolia was obviously increased under the moderate and severe drought stress. With the increases of drought stress, Fv/Fo, Fv/Fm, qP, ETR and ФPS2 gradually decreased, and NPQ gradually increased. The changes of all those characters after rewatering were contrary to those after drought. After rewatering for eight days, Fv/Fo, Fv/Fm, qP, ETR, ФPS2 were significantly higher than that of drought stress treated for 30 days. With the increases of drought stress, SOD and POD activities and MDA content gradually increased, but CAT activity decreased, showing the contrary changes after rewatering. After rewatering, the root activity under drought stress increased. X. sorbifolia was strongly resistant to heavy drought stress, and thus could be widely used as energy or garden plants in garden landscaping in North China.
Subject(s)
Droughts , Photosynthesis , Sapindaceae/physiology , China , Chlorophyll , Plant Leaves , WaterABSTRACT
The preparation of novel steroidal heterocycles containing the 7-aryl-substituted 1,2,4-triazolo[1,5-a]pyrimidine moiety fused to the 16,17-positions of the steroid nucleus is described. The Aldol reaction of 4-aza-androst-3,17-dione (1a) and dehydroepiandrosterone (DHEA, 1b) with aromatic aldehydes was catalyzed by KF/Al(2)O(3) to give the corresponding 3-oxo-4-aza-5α- and 3ß-hydroxy-5-en-16-arylidene-17-ketosteroids (2a-r). Subsequently, the intermediates 2a-r reacted with dinucleophilic 3-amino-1,2,4-triazole in presence of t-BuOK to afford the title compounds (3a-r). All the synthesized heterosteroids are new and are currently being evaluated for their biological activities.
