Ultrathin coatings
(1.5 ± 0.3 nm) of titanium dioxide and
zinc oxide were deposited on lithium-rich layered oxide cathodes (Li1.2Mn0.6Ni0.2O2, LLO) by atomic
layer deposition (ALD). The structures, electrochemical performances,
and thermal stabilities of these coatings were investigated. An ultrathin
uniform coating was obtained for TiO2 but not for ZnO because
of differences in the layer growth mechanism. Regarding the initial
charge–discharge curves under a current density of 0.04 C rate,
the TiO2 coated samples exhibited a higher discharge capacity,
242 mAhg–1, compared with the ZnO coated samples,
220 mAhg–1, or the pristine samples, 228 mAhg–1. Both coated samples exhibited more stable cycling
performance and thermal stability than the pristine samples. After
80 cycles under 0.5 C rate, the TiO2 and ZnO coated samples
were found to have higher capacity retention (∼94% and 78%,
respectively) than the pristine samples (68%). The reaction temperature
of the exothermic peak of the TiO2 and ZnO coated samples
at 4.8 V shifted to 280 °C with heat release of 88.7 J/g for
TiO2 and 270 °C with heat release of 154.6 J/g for
ZnO. This is compared with an exothermic peak at 258 °C with
heat release of 253.5 J/g for the pristine sample. In particular,
an enhanced rate capability was only observed for the TiO2 coated samples. When the current densities were higher than 2 C
rate, the TiO2 coated samples exhibited superior capacities
than the pristine and ZnO coated samples. At a current density of
5 and 10 C rate, the capacities were found to be 120 and 95 mAhg–1. The improved electrochemical performances were mainly
attributed to lower resistance of the charge transfer, which resulted
from the layer morphology of the TiO2 film. This feature
lead to more preactivation of LLO, smoother electron transport, and
suppression of more side reactions, when compared with the island
structure of the ZnO film.
The use of electricity to treat water was employed for the first time in the UK a century ago, and since then has been considered a highly reliable method for wastewater treatment. In recent years, the demand for hydrogen gas as a valuable, clean energy source has increased considerably; from this point of view, the electrolysis of wastewater can meet the demand for energy during the process of treating wastewater. In this work, wastewater containing heavy metal ions has been treated by an electrochemical method which not only decreased the chemical oxygen demand value and lowered the number of heavy metals ions but also generated hydrogen throughout the process. A series of experiments were performed under optimum conditions of selected electrode materials, pH values, supply power, and working time. The results obtained indicate that by controlling the key factors of the process, a practical method can be achieved for wastewater treatment which also produces a noticeable amount of green energy. Differential pulse voltammetry measurements were used to determine the properties of an industrial wastewater source before and after treatment, while scanning electron microscopy and energy dispersive X‐ray spectroscopy were applied to investigate the proficiency of the electrode material.
Thin films of carbon-mixed
LiFePO4
were deposited on Si and stainless steel substrates by radio-frequency magnetron sputtering. The goal of this study was to optimize the conditions of sputter deposition for
LiFePO4∕C
thin films to obtain a film with pure
LiFePO4
phase. Negative electric bias
(0−80V)
was applied on the substrates during deposition to modify the film properties. After deposition, the films were annealed at different temperatures ranging from
150–650°C
without leaving the vacuum deposition chamber. Suitable bias was found to purify the
LiFePO4
olivine phase and reduce the grain size. Too high a substrate bias and anneal temperature resulted in undesired second phases. Carbon mixing effectively lowered the resistivity of the films to the order of
102Ωcm
. Charge-discharge and cyclic voltammetry curves revealed the different electrochemical characteristics of these films, which were attributed to the modified crystallography and morphology. The films deposited under substrate bias of
−20V
and anneal temperature of
500°C
exhibited a capacity of
∼170mAhg±7.5%
with a
3.4V
plateau.
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