ABSTRACT
Electrochemical irreversibility and sluggish mobility of Na+ in the cathode materials result in poor cycle stability and rate capability for sodium-ion batteries. Herein, a new strategy of introducing Mg ions into the hinging sites of Mn-based tunnel-structured cathode material is designed. Highly reversible electrochemical reaction and phase transition in this cathode are realized. The resulted Na0.44Mn0.95Mg0.05O2 with Mg2+ in the hinging Mn-O5 square pyramidal exhibits promising cycle stability and rate capability. At a current density of 2 C, 67% of the initial discharge capacity is retained after 800 cycles (70% at 20 C), much improved than the undoped Na0.44MnO2. The improvement is attribute to the enhanced Na+ diffusion kinetics and the lowered desodiation energy after Mg doping. Highly reversible charge compensation and structure evolution are proved by synchrotron-based X-ray techniques. Differential charge density and atom population analysis of the average electron number of Mn indicate that Na0.44Mn0.95Mg0.05O2 is more electron-abundant in Mn 3d orbits near the Fermi level than that in Na0.44MnO2, leading to higher redox participation of Mn ions.
ABSTRACT
Lithium-sulfur (Li-S) batteries have been regarded as a promising candidate of secondary batteries to satisfy the enormous demand for electric vehicles and energy storage applications. However, Li-S batteries still suffer from severe capacity fading due to the shuttle effect of lithium polysulfides. Here, we develop a freestanding double-layer MoO3/carbon nanotube@S (FMC@S) membrane by hydrothermal and suction filtration strategy, without polymer binder and current collector substrate. FMC@S contains a polysulfide blocking layer and an active material layer. Except for S content, the two layers have the same components and are integrated together, so there is no distinct interface between the two layers, which can facilitate ion and electron transport. As a result, the FMC@S cathode delivers promising capacity retention and rate capability. The hierarchical integrated design provides a new strategy to develop high-performance flexible cathodes for Li-S batteries.
ABSTRACT
LiNi0.8Co0.15Al0.05O2 (NCA) has been proven to be a good cathode material for lithium-ion batteries (LIBs), especially in electric vehicle applications. However, further elevating energy density of NCA is very challenging. Increasing the charging voltage of NCA is an effective method, but its structural instability remains a problem. In this work, we revealed that titanium substitution could improve cycle stability of NCA under high cutoff voltage significantly. Titanium ions with a relatively larger ion radius could modify the oxygen lattice and change the local coordination environment of NCA, leading to decreased cation migration, better kinetic and thermodynamic properties, and improved structural stability. As a result, the Ti-substituted NCA cathode exhibits impressive reversible capacity (198 mA h g-1 at 0.1C) with considerable cycle stability under a cutoff voltage up to 4.7 V. It is also revealed that Ti could suppress oxygen release in the high-voltage region, benefitting cycle and thermal stabilities. This work provides valuable insight into the design of high-voltage layered cathode materials for high-energy-density LIBs.
ABSTRACT
Most P2-type layered oxides suffer from multiple voltage plateaus, due to Na+/vacancy-order superstructures caused by strong interplay between Na-Na electrostatic interactions and charge ordering in the transition metal layers. Here, Mg ions are successfully introduced into Na sites in addition to the conventional transition metal sites in P2-type Na0.7[Mn0.6Ni0.4]O2 as new cathode materials for sodium-ion batteries. Mg ions in the Na layer serve as "pillars" to stabilize the layered structure, especially for high-voltage charging, meanwhile Mg ions in the transition metal layer can destroy charge ordering. More importantly, Mg ion occupation in both sodium and transition metal layers will be able to create "Na-O-Mg" and "Mg-O-Mg" configurations in layered structures, resulting in ionic O 2p character, which allocates these O 2p states on top of those interacting with transition metals in the O-valence band, thus promoting reversible oxygen redox. This innovative design contributes smooth voltage profiles and high structural stability. Na0.7Mg0.05[Mn0.6Ni0.2Mg0.15]O2 exhibits superior electrochemical performance, especially good capacity retention at high current rate under a high cutoff voltage (4.2 V). A new P2 phase is formed after charge, rather than an O2 phase for the unsubstituted material. Besides, multiple intermediate phases are observed during high-rate charging. Na-ion transport kinetics are mainly affected by elemental-related redox couples and structural reorganization. These findings will open new opportunities for designing and optimizing layer-structured cathodes for sodium-ion batteries.
ABSTRACT
This study is to explore the effects of quercetin (QUE) on the 3 week-old mice ovarian development and relative hormone levels. The 3 week-old mice were exposed to QUE (45, 25, and 5 mg x kg(-1) x hd(-1)) by gavage for 50 days. The estrous cycle during 50 days and the changes of hormone level such as FSH, LH, etc were monitored. Moreover, the ovaries were removed after sacrifice. The organ index was measured, and the ratios of different stages of follicles were analyzed by HE staining. Furthermore, the proportion of PCNA positive cells during all stages was detected by immunohistochemistry. The results showed that QUE could increase body weight of mice and reduce the anogenital distance (AGD) to some extent, and was able to disrupt mice's estrous cycle, but it could not extend or reduce the cycle regularity. It increased ovarian organ index with a dose-dependent manner. The proportion of the primordial follicle and secondary follicles rose obviously, and that of mature follicles', atretic follicles' and corpus luteums' reduced, while primordial follicle had no change. Immunohistochemistry analysis showed that QUE could effectively increase the percentage of proliferating cells in all kinds of follicles. Serum hormone assay showed that there were significant changes of FSH and LH levels. In summary, QUE showed an estrogen-like effect on mice's ovarian development. The weight of ovary, the proportion of all kinds of follicles, the development of ovarian cells and the level of plasma hormone in mice were altered obviously by oral administration of QUE.
