No abstract

LiNi 1−x−y Co x Al y O 2 (NCA) possessing a nano-/micro hierarchical architecture delivers a high specific capacity of 200 mAh/g with an upper cutoff voltage of 4.4 V. However, the structural reconstruction due to the irreversibility of the H2 ↔ H3 phase transition at higher voltage increases the initial irreversible capacity loss and charge-transfer impedance and reduces the performance at higher C-rates. Structural and electrochemical stability can be achieved by reducing the nickel content and increasing the electrochemically inactive aluminum at the surface. Nonetheless, getting an aluminum concentration gradient in NCA−(OH) 2 is difficult owing to the difference in the solubility constant and reaction kinetics of Al(OH) 3 compared to that of NiCo−(OH) 2 . Hence, we have exploited the high diffusion of nano-Al(OH) 3 driven by the concentration gradient of Al across the hierarchical hydroxide structure and synthesized LiNi 0.8 Co 0.135 Al 0.065 O 2 (NCA) with reduced Ni and increased Al at the surface. The process of formation of a concentration gradient was analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and cross-sectional elemental mapping. The concentration-graded NCA exhibited superior electrochemical performance compared to its pristine counterpart. The graded NCA shows excellent reversibility of the H2 ↔ H3 phase, leading to low impedance development, confirming the reduced surface reconstruction during the initial cycles. Therefore, the specific capacity of graded NCA is 65% higher than that of pristine NCA at 10 C. Both in half-cell and in full-cell configurations, the graded NCA exhibited superior first cycle reversibility and specific capacity. Specifically, in the full-cell configuration, the capacity retention of graded NCA is 91.5%, while that of pristine NCA is 83% after 150 cycles when cycled between 3 and 4.3 V. Further, the capacity loss reduces to 1% even after 500 cycles when the upper cutoff voltage is reduced to 4.2 V in the case of graded NCA.

No abstract

In this paper we describe the design of a simple Bridgman opposed anvil cell to measure the thermoelectric power of solids as a function of pressure up to 100 kbar. The anvils are made of EN-24 alloy steel hardened to RC55.

No abstract