7 research outputs found
Self-Terminated Artificial SEI Layer for Nickel-Rich Layered Cathode Material via Mixed Gas Chemical Vapor Deposition
Because of the higher specific capacity,
nickel-rich layered cathode
material has received much attention from the lithium-ion battery
community. However, its cycle life is desired to improve further for
practical applications, and unstable interface with electrolyte is
one of the main capacity fading mechanisms. Here, we report a facile
chemical vapor deposition process involving mixed gases of CO<sub>2</sub> and CH<sub>4</sub>, which yields thin and conformal artificial
solid-electrolyte-interphase (SEI) layer consisting of alkyl lithium
carbonate (LiCO<sub>3</sub>R) and lithium carbonate (Li<sub>2</sub>CO<sub>3</sub>) on nickel-rich active cathode powder. The coating
layer protects from side reactions and improves the cycle life and
efficiency significantly. Remarkably, the coating process is self-terminated
after the thickness reaches ā¼10 nm, leading to the coating
layer to account for only 0.48 wt %, because of the growing binding
energy between the gas mixture and the surface products. The self-termination
is characterized by various analytical tools and is well-explained
by density functional theory calculations. The current gas phase coating
process should be applicable to other battery materials that suffer
from continuous side reactions with electrolyte
Na<sup>+</sup>/Vacancy Disordered P2-Na<sub>0.67</sub>Co<sub>1ā<i>x</i></sub>Ti<i><sub>x</sub></i>O<sub>2</sub>: High-Energy and High-Power Cathode Materials for Sodium Ion Batteries
Although
sodium ion batteries (NIBs) have gained wide interest, their poor
energy density poses a serious challenge for their practical applications.
Therefore, high-energy-density cathode materials are required for
NIBs to enable the utilization of a large amount of reversible Na
ions. This study presents a P2-type Na<sub>0.67</sub>Co<sub>1ā<i>x</i></sub>Ti<i><sub>x</sub></i>O<sub>2</sub> (<i>x</i> < 0.2) cathode with an extended potential range higher
than 4.4 V to present a high specific capacity of 166 mAh g<sup>ā1</sup>. A group of P2-type cathodes containing various amounts of Ti is
prepared using a facile synthetic method. These cathodes show different
behaviors of the Na<sup>+</sup>/vacancy ordering. Na<sub>0.67</sub>CoO<sub>2</sub> suffers severe capacity loss at high voltages due
to irreversible structure changes causing serious polarization, while
the Ti-substituted cathodes have long credible cycleability as well
as high energy. In particular, Na<sub>0.67</sub>Co<sub>0.90</sub>Ti<sub>0.10</sub>O<sub>2</sub> exhibits excellent capacity retention (115
mAh g<sup>ā1</sup>) even after 100 cycles, whereas Na<sub>0.67</sub>CoO<sub>2</sub> exhibits negligible capacity retention (<10 mAh
g<sup>ā1</sup>) at 4.5 V cutoff conditions. Na<sub>0.67</sub>Co<sub>0.90</sub>Ti<sub>0.10</sub>O<sub>2</sub> also exhibits outstanding
rate capabilities of 108 mAh g<sup>ā1</sup> at a current density
of 1000 mA g<sup>ā1</sup> (7.4 C). Increased sodium diffusion
kinetics from mitigated Na<sup>+</sup>/vacancy ordering, which allows
high Na<sup>+</sup> utilization, are investigated to find in detail
the mechanism of the improvement by combining systematic analyses
comprising TEM, in situ XRD, and electrochemical methods
Physically Cross-linked Polymer Binder Induced by Reversible AcidāBase Interaction for High-Performance Silicon Composite Anodes
Silicon is greatly promising for
high-capacity anode materials in lithium-ion batteries (LIBs) due
to their exceptionally high theoretical capacity. However, it has
a big challenge of severe volume changes during charge and discharge,
resulting in substantial deterioration of the electrode and restricting
its practical application. This conflict requires a novel binder system
enabling reliable cyclability to hold silicon particles without severe
disintegration of the electrode. Here, a physically cross-linked polymer
binder induced by reversible acidābase interaction is reported
for high performance silicon-anodes. Chemical cross-linking of polymer
binders, mainly based on acidic polymers including polyĀ(acrylic acid)
(PAA), have been suggested as effective ways to accommodate the volume
expansion of Si-based electrodes. Unlike the common chemical cross-linking,
which causes a gradual and nonreversible fracturing of the cross-linked
network, a physically cross-linked binder based on PAAāPBI
(polyĀ(benzimidazole)) efficiently holds the Si particles even after
the large volume changes due to its ability to reversibly reconstruct
ionic bonds. The PBI-containing binder, PAAāPBI-2, exhibited
large capacity (1376.7 mAh g<sup>ā1</sup>), high Coulombic
efficiency (99.1%) and excellent cyclability (751.0 mAh g<sup>ā1</sup> after 100 cycles). This simple yet efficient method is promising
to solve the failures relating with pulverization and isolation from
the severe volume changes of the Si electrode, and advance the realization
of high-capacity LIBs
Surface Modification of Sulfur Electrodes by Chemically Anchored Cross-Linked Polymer Coating for LithiumāSulfur Batteries
Lithiumāsulfur
batteries suffer from severe self-discharge
due to polysulfide dissolution into electrolytes. In this work, a
chemically anchored polymer-coated (CAPC) sulfur electrode was prepared,
through chemical bonding by coordinated Cu ions and cross-linking,
to improve cyclability for Li/S batteries. This electrode retained
specific capacities greater than 665 mAh g<sup>ā1</sup> at
high current density of 3.35 A g<sup>ā1</sup> (2<i>C</i> rate) after 100 cycles with an excellent Coulombic efficiency of
100%
Bi-Morphological Form of SiO<sub>2</sub> on a Separator for Modulating Li-Ion Solvation and Self-Scavenging of Li Dendrites in Li Metal Batteries
The
lithium (Li) metal anode is highly desirable for high-energy
density batteries. During prolonged Li platingāstripping, however,
dendritic Li formation and growth are probabilistically high, allowing
physical contact between the two electrodes, which results in a cell
short-circuit. Engineering the separator is a promising and facile
way to suppress dendritic growth. When a conventional coating approach
is applied, it usually sacrifices the bare separator structure and
severely increases the thickness, ultimately decreasing the volumetric
density. Herein, we introduce dielectric silicon oxide with the feature
of bi-morphological form, i.e., backbone-covered and backbone-anchored,
onto the conventional polyethylene separator without any volumetric
change. These functionally vary the Li+ transference number
and the ionic conductivity so as to modulate Li-ion solvation and
self-scavenging of Li dendrites. The proposed separator paves the
way to maximizing the full cell performance of Li/NCM622 toward practical
application