RESUMO
Tremendous effort has been devoted to develop durable electrode materials for sodium ion batteries. This work focuses on enhancing the reversibility of a cathode material Na0.5Ni0.25Mn0.75O2 by adopting the titanium cation doping strategy. The obtained P2-Na0.5Ni0.25Mn0.60Ti0.15O2 material shows smooth charge-discharge curves upon suppressing the Na+/vacancy ordering effect via the partial substitution of Mn4+ for Ti4+, and enhanced cycling performance. It exhibits a reversible capacity of 138 mA h g-1 at 0.5C, as well as a high rate capacity of 81 mA h g-1 at 5C between a cut-off voltage of 2 and 4 V, while long-term cycling stability is demonstrated with a capacity retention of 84% over 200 cycles. An enhanced cycling stability is also observed when the voltage is between 2 and 4.2 V. The feasibility of constructing a symmetrical Na-ion full cell with Na0.5Ni0.25Mn0.60Ti0.15O2 as cathode and anode electrodes is also demonstrated. The titanium cation doping results in reduced charge transfer impedance and an enhanced sodium cation diffusion coefficient, thus suggesting an efficient strategy to obtain a durable cathode material for sodium ion batteries.
RESUMO
Considering the abundance of iron and manganese within the Earth's crust, the cathode O3-NaFe0.5Mn0.5O2 has shown great potential for large-scale energy storage. Following the strategy of introducing specific heteroelements to optimize the structural stability for energy storage, the work has obtained an O3-type NaFe0.4Mn0.49Cu0.1Zr0.01O2 that exhibits enhanced electrochemical performance and air stability. It displays an initial reversible capacity of 147.5 mAh g-1 at 0.1C between 2 and 4.1 V, a capacity retention ratio exceeding 69.6% after 100 cycles at 0.2C, and a discharge capacity of 70.8 mAh g-1 at a high rate of 5C, which is superior to that of O3-NaFe0.5Mn0.5O2. The codoping of Cu/Zr reserves the layered O3 structure and enlarges the interlayer spacing, promoting the diffusion of Na+. In addition, the structural stability and air stability observed by Cu-doping is well maintained via the incorporation of extra Zr favoring a highly reversible phase conversion process. Thus, this work has demonstrated an efficient strategy for developing cobalt/nickel-free high-capacity and air-stable cathodes for sodium-ion batteries.
RESUMO
Sodium-ion batteries (SIBs) are recognized as attractive alternatives for grid-scale electrochemical energy storage applications. Transition metal oxide cathodes represent one of the most dynamic materials for industrialization among the various cathodes for SIBs. Here, a cation-doped cathode Na0.44Mn0.89Ti0.11O2 with a tunnel structure is introduced, which undergoes a lowered volume change of only 5.26% during the Na+ insertion/extraction process. Moreover, the average Na+ diffusion coefficients are enhanced by more than 3-fold upon the doping of the Ti cation. The obtained cathode delivers a practically usable capacity of 119 mAh g-1 at 0.1 C as well as an enhanced discharge capacity of 96 mAh g-1 at 5 C. Durability is demonstrated by the retained 71 mAh g-1 after 1000 cycles, corresponding to a capacity retention of 74%. This work demonstrates that the reticular Na0.44Mn0.89Ti0.11O2 is a promising ultrastable cathode material for the development of long-life sodium-ion batteries.
RESUMO
OBJECTIVE: To observe the effect of acupoint application at bilateral "Tianshu" (ST25) on intestinal mobility and immunoactivity of vasoactive intestinal peptide (VIP) and substance P (SP) in colonic myenteric plexus of rats with functional constipation (FC), so as to analyze its mechanisms underlying improving FC. METHODS: Forty male SD rats were randomly divided into 4 groups, namely normal control, model, acupoint application and medication, with 10 rats in each group. The FC model was established by gavage of Loperamide Hydrochloride suspension fluid (0.5 mg/mL, 3 mg·kg-1·d-1) for 7 days. Herbal medicine paste (composed of Rheum Officinale, Sodium Sulfate, Mangnolia Officinalis, etc.) was applied to bilateral ST25 for 6 h, once daily for 4 weeks. Rats of the medication group were treated by gavage of Mosapride suspension fluid (0.15 mg/mL, 1.58 mg·kg-1·d-1) for 4 weeks. After the treatment, the rats were deprived of water for 12 hours, and then treated by gavage of 2 mL of activated carbon suspension, followed by recording the first black defecation time and the number of fecal particles and water content of feces within 6 h so as to assess the intestinal mobility. The immunoactivity and average surface density of VIP and SP positive granules in the colonic myenteric plexus were detected by immunohistochemistry. RESULTS: Compared with the normal control group, the first black defecation time was significantly prolonged, and the number and water content of fecal particles within 6 h, and the expression and the average surface density of VIP and SP were significantly reduced in the model group (P<0.01). After the treatment and compared with the model group, the first black defecation time was shortened, and the fecal water content and fecal particle number within 6 h, as well as the expression and the average surface density of VIP and SP were considerably increased in both acupoint application and medication groups (P<0.01). There were no significant differences between the acupoint application and medication groups in all the indexes mentioned above after the interventions (P>0.05). CONCLUSION: Acupoint application may improve the intestinal motility in FC rats, which may be asso-ciated with its effects in up-regulating the immunoactivity of VIP and SP in colonic myenteric plexus of the large intestine.