Peng Li,Lianyi Shao,Pengfei Wang,Xi Zheng,Haoxiang Yu,Shangshu Qian,Miao Shui,Nengbing Long,Jie Shu
In this work, Li 2 NaV 2 (PO 4 ) 3 is successfully synthesized by using a simple solid-state reaction method. Structural analysis shows that this sample is a hybrid product consisted of rhombohedral Li 3 V 2 (PO 4 ) 3 phase and rhombohedral Na 3 V 2 (PO 4 ) 3 phase As a cathode material for lithium ion batteries, Li 2 NaV 2 (PO 4 ) 3 exhibits an initial reversible capacity of 108.9 mAh g −1 at 35 mA g −1 in the potential range between 3.0 and 4.3 V, with an average working potential at 3.75 V. The lithium-ion diffusion coefficient in Li 2 NaV 2 (PO 4 ) 3 is measured to be 1.86–3.27 × 10 −15 cm 2 s −1 . In addition, the electrochemical reaction between Li 2 NaV 2 (PO 4 ) 3 and Li is also investigated by various in-situ and ex-situ techniques. Viewed from the in-situ and ex-situ results, it is concluded that the electrochemical reactions of Li 2 NaV 2 (PO 4 ) 3 with Li are associated with the formation of rhombohedral LiV 2 (PO 4 ) 3 phase and rhombohedral NaV 2 (PO 4 ) 3 phase during the lithium ion extraction process and its reverse lithium insertion process is reversible for structural evolution. The highly stable structure ensures the electrochemical reversibility of Li 2 NaV 2 (PO 4 ) 3 cathode material in lithium ion batteries.
The microstructure of plasma-sprayed nanostructured yttria-stabilized zirconia (YSZ) coatings may change during high-temperature exposure, which would influence the coating performance and service lifetime. In this study, the phase structure and the microstructural evolution of 3YSZ (zirconia-3 mol% yttria) and 5YSZ (zirconia-5 mol% yttria) nanostructured coatings were investigated by means of sintering at 1400 °C for 50–100 h. The microhardness, elastic moduli, and thermal shock cycles of the 3YSZ and 5YSZ nanostructured coatings were also investigated. The results showed that the redistribution of yttrium ions at 1400 °C caused the continuous increase of monoclinic-phase zirconia, but no obvious inter-splat cracking formed at the cross-sections, even after 100 h. Large voids appeared around the nanoporous zone because of the sintering of nanoscale granules upon high-temperature exposure. The microhardness and elastic moduli of the nanostructured coatings first increased and then decreased with increasing sintering times. The growth rate of the nanograins in the 3YSZ coating was lower than that in 5YSZ, which slowed the changes in 3YSZ coating porosity during sintering. Although the 3YSZ coating was prone to monoclinic phase transition, the experimental results showed that the thermal shock resistance of the 3YSZ coating was better than that of the 5YSZ coating.
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