Danni Lei

Acetic acid-induced preparation of anatase TiO2 mesocrystals at low temperature for enhanced Li-ion storage

Titanium dioxide (TiO2) mesocrystals consist of a large number of subunits possessing distinct characteristics of large surface area, high crystallinity and large density and are considered as promising potential materials for energy storage and conversion, sensing, and photocatalysis. Therefore, it is significant to develop a robust and universal method to synthesize and precisely tune the TiO2 mesocrystals at low temperatures. However, this is still a big challenge and has not been largely achieved. In this context, we develop a robust method of synthesizing TiO2 mesocrystals by a facile hydrolysis and evolution process induced by acetic acid (HAc) solution at 80 °C using TiN as a starting material. The size and crystallinity of the TiO2 mesocrystals can be easily tuned by adjusting the HAc content and reaction time. The HAc governs the transformation of TiO2 from the amorphous state to the anatase phase at a low temperature (80 °C). The average size of the TiO2 mesocrystals can be tuned from ∼100 nm to 20 nm by changing the HAc content. TiO2 mesocrystals with a spindle-like morphology were formed and the tiny anatase TiO2 grains were grown along the same orientation [001] plane, which exhibits excellent electrochemical performance for lithium-ion storage. The specific capacity at 1C is 180 mA h g−1 and the retention is 92.9% after 100 cycles. Thereby, this study presents a universal method of crafting anatase TiO2 mesocrystals at low temperatures.

Deterioration mechanism of LiNi0.8Co0.15Al0.05O2/graphite–SiOx power batteries under high temperature and discharge cycling conditions

LiNi0.8Co0.15Al0.05O2 and graphite–SiOx composites have been considered as potential cathode and anode materials for next-generation batteries due to their high specific capacity. It is significant to illustrate the degradation mechanism of NCA/graphite–SiOx power batteries under various conditions for their wide application. In this study, 10 A h NCA/graphite–SiOx power batteries were prepared and their deterioration mechanism at different temperatures (25 °C, 45 °C, and 65 °C) and discharge rates (1C and 3C) was systematically investigated. The results show that the batteries experienced 15.02% and 52.17% capacity loss after 400 cycles at 25 °C and 45 °C at 1C, respectively, and 21.94% after 400 cycles at a discharge rate of 3C. The capacity loss is as high as 79.93% after only 150 cycles at 65 °C and 1C. The long-term cycling behavior of the batteries is strongly affected by temperature, whereas it is negligibly affected by the discharge rate. The reversible lithium loss from the NCA cathode and structure decay of graphite–SiOx are responsible for the capacity loss of the battery. Many lithium alkyl carbonate (Li2CO3 and ROCO2Li), fluorophosphate (LixPOyFz and LixPFy), LiF, and oxygenated species are observed on the surface of graphite–SiOx due to the decomposition of the electrolyte at high temperatures. These species are deposited on the separator and thus block the pores and hinder ion transport; this results in a great increase of battery resistance and sudden loss of battery capacity.

Spherical Li Deposited inside 3D Cu Skeleton as Anode with Ultrastable Performance

Porous current collectors are conducive to enhance the property of Li metal anode. Unfortunately, congestion in diffusion path during plating process damages the effects of current collectors. Herein, we developed a 3D Cu skeleton with open micrometer-sized pores by NaCl-assisted powder-sintering method. The unobstructed pores of 3D Cu skeleton help to reduce congestion during plating, thus most of Li deposited inside the current collector. Besides, the large smooth surface promotes the deposition of Li with smooth spherical shape, which mitigating Li dendrite growth. As a result, better safety and rechargeability of Li metal anode were achieved in this design.