22 research outputs found
World Minerals and World Politics
Geometry of carbon
supports significantly affected electrochemical durability of Pt/C
(platinum electrocatalyst supported by carbon) for oxygen reduction
reaction (ORR). Carbon nano-onion (CNO) was used as the support, which
is characterized by its nanosize (similar to Pt size) and high curvature.
Superior ORR durability was guaranteed by Pt/CNO due to (1) its <i>islands-by-islands</i> configuration to isolate each Pt nanoparticle
from its neighbors by CNO particles; (2) highly tortuous void structure
of the configuration to suppress Ostwald ripening; and (3) the <i>curvature-induced strong interaction</i> between CNO and Pt.
The finding that highly curved carbon surface encourages electron
donation to catalysts was first reported
Multiple Roles of Superoxide on Oxygen Reduction Reaction in Li<sup>+</sup>‑Containing Nonaqueous Electrolyte: Contribution to the Formation of Oxide as Well as Peroxide
Oxygen reduction reaction (ORR) on
carbon in lithium-ion-containing
nonaqueous electrolytes is supposed to follow a three-step mechanism:
oxygen (O<sub>2</sub><sup>0</sup>) to superoxide (O<sub>2</sub><sup>–</sup> or LiO<sub>2</sub>) to peroxide (O<sub>2</sub><sup>2–</sup> or Li<sub>2</sub>O<sub>2</sub>) to oxide (O<sup>2–</sup> or Li<sub>2</sub>O). This work attempts to solve three controversial
issues: (1) whether the superoxide is really formed; (2) whether the
superoxide can be stable or immediately converts to peroxide; (3)
whether the formation of oxide is feasible at the typical discharge
potentials of lithium–air battery or the discharge product
is only peroxide. ORR on carbon was studied in LiClO<sub>4</sub> or
LiPF<sub>6</sub> containing dimethyl sulfoxide. The staircase cyclic
voltammetry combined with Fourier transform electrochemical impedance
spectroscopy (SCV-FTEIS) was used for the <i>in situ</i> investigation of ORR during potential scans. Oxygen was quasi-reversibly
reduced to superoxide in the first step. Superoxide showed chemical
stability in electrolyte. The superoxide was further reduced to surface-adsorbed
peroxide, and the reduction proceeded to produce oxide at higher overpotentials.
We identified a novel chemical route resulting in oxide formation
even at not-enough overpotentials: peroxide is reduced to oxide by
superoxide as an <i>in situ</i> formed one-electron reducing
agent. The electrolyte/electrode decomposition product, Li<sub>2</sub>CO<sub>3</sub>, was observed only in electrolyte with LiClO<sub>4</sub>
Facile Route to an Efficient NiO Supercapacitor with a Three-Dimensional Nanonetwork Morphology
NiO nanostructures with three distinct
morphologies were fabricated by a sol–gel method and their
morphology-dependent supercapacitor properties were exploited. The
nanoflower- shaped NiO with a distinctive three-dimensional (3D) network
and the highest pore volume shows the best supercapacitor properties.
The nanopores in flower-shaped nanostructures, offering advantages
in contact with and transport of the electrolyte, allow for 3D nanochannels
in NiO structure, providing longer electron pathways. The XPS and
EIS data of the NiO nanostructure confirm that the flower-shaped NiO,
which has the lowest surface area among the three morphologies, was
effectively optimized as a superior electrode and yielded the greatest
pseudocapacitance. This study indicates that forming a 3D nanonetwork
is a straightforward means of improving the electrochemical properties
of a supercapacitor
Succinonitrile as a Corrosion Inhibitor of Copper Current Collectors for Overdischarge Protection of Lithium Ion Batteries
Succinonitrile (SN) is investigated
as an electrolyte additive for copper corrosion inhibition to provide
overdischarge (OD) protection to lithium ion batteries (LIBs). The
anodic Cu corrosion, occurring above 3.5 V (vs Li/Li<sup>+</sup>)
in conventional LIB electrolytes, is suppressed until a voltage of
4.5 V is reached in the presence of SN. The corrosion inhibition by
SN is ascribed to the formation of an SN-induced passive layer, which
spontaneously develops on the copper surface during the first anodic
scan. The passive layer is composed mainly of Cu(SN)<sub>2</sub>PF<sub>6</sub> units, which is evidenced by Raman spectroscopy and electrochemical
quartz crystal microbalance measurements. The effects of the SN additive
on OD protection are confirmed by using 750 mAh pouch-type full cells
of LiCoO<sub>2</sub> and graphite with lithium metal as a reference
electrode. Addition of SN completely prevents corrosion of the copper
current collector in the full cell configuration, thereby tuning the
LIB chemistry to be inherently immune to the OD abuses
Conducting Polymer-Skinned Electroactive Materials of Lithium-Ion Batteries: Ready for Monocomponent Electrodes without Additional Binders and Conductive Agents
Rapid
growth of mobile and even wearable electronics is in pursuit of high-energy-density
lithium-ion batteries. One simple and facile way to achieve this goal
is the elimination of nonelectroactive components of electrodes such
as binders and conductive agents. Here, we present a new concept of
monocomponent electrodes comprising solely electroactive materials
that are wrapped with an insignificant amount (less than 0.4 wt %)
of conducting polymer (PEDOT:PSS or poly(3,4-ethylenedioxythiophene)
doped with poly(styrenesulfonate)). The PEDOT:PSS as an ultraskinny
surface layer on electroactive materials (LiCoO<sub>2</sub> (LCO)
powders are chosen as a model system to explore feasibility of this
new concept) successfully acts as a kind of binder as well as mixed
(both electrically and ionically) conductive film, playing a key role
in enabling the monocomponent electrode. The electric conductivity
of the monocomponent LCO cathode is controlled by simply varying the
PSS content and also the structural conformation (benzoid-favoring
coil structure and quinoid-favoring linear or extended coil structure)
of PEDOT in the PEDOT:PSS skin. Notably, a substantial increase in
the mass-loading density of the LCO cathode is realized with the PEDOT:PSS
skin without sacrificing electronic/ionic transport pathways. We envisage
that the PEDOT:PSS-skinned electrode strategy opens a scalable and
versatile route for making practically meaningful binder-/conductive
agent-free (monocomponent) electrodes
Activity-Durability Coincidence of Oxygen Evolution Reaction in the Presence of Carbon Corrosion: Case Study of MnCo<sub>2</sub>O<sub>4</sub> Spinel with Carbon Black
Highly oxygen evolution
reaction (OER)-active electrocatalysts
often exhibit improved OER durability in the presence of carbon corrosion
or oxidation (COR) in the literature. The activity-durability coincidence
of OER electrocatalysts was theoretically understood by preferential
depolarization in galvanostatic situations. At constant-current conditions
for a system involving multiple reactions that are independent and
competitive, the overpotential is determined most dominantly by the
most facile reaction so that the most facile reaction is responsible
for a dominant portion of the overall current. Therefore, higher OER
activity improves durability by mitigating the current responsible
for COR. The activity-durability coincidence was then proved experimentally
by comparing between two catalysts of the same chemical identity (MnCo<sub>2</sub>O<sub>4</sub>) in different dimensions (5 and 100 nm in size).
Carbon corrosion responsible for inferior durability was suppressed
in the smaller-dimension catalyst (MnCo<sub>2</sub>O<sub>4</sub> in
5 nm) having more numbers of active sites per a fixed mass
Influence of the Lithium-Ion Concentration in Electrolytes on the Performance of Dye-Sensitized Photorechargeable Batteries
Dye-sensitized photorechargeable batteries (DSPBs) have
recently
gained attention for realizing energy recycling systems under dim
light conditions. However, their performance under high storage efficiency
(i.e., the capacity charged within a limited time) for practical application
remains to be evaluated. Herein, we varied the lithium (Li)-ion concentration,
which plays a dual role as energy charging and storage components,
to obtain the optimized energy density of DSPBs. Electrochemical studies
showed that the Li-ion concentration strongly affected the resistance
characteristics of DSPBs. In particular, increasing the Li-ion concentration
improved the output capacity and decreased the output voltage. Consequently,
the energy density of the finely optimized DSPB improved from 8.73
to 12.64 mWh/cm3 when irradiated by a 1000-lx indoor light-emitting-diode
lamp. These findings on the effects of Li-ion concentrations in electrolytes
on the performance of DSPBs represent a step forward in realizing
the practical application of DSPBs
Amphi-Active Superoxide-Solvating Charge Redox Mediator for Highly Stable Lithium–Oxygen Batteries
A multifunctional electrolyte additive for lithium oxygen
batteries
(LOBs) was designed to have (1) a redox-active moiety to mediate decomposition
of lithium peroxide (Li2O2 as the final discharge
product) during charging and (2) a solvent moiety to solvate and stabilize
lithium superoxide (LiO2 as the intermediate discharge
product) in electrolyte during discharging. 4-Acetamido-TEMPO (TEMPO
= 2,2,6,6-tetramethylpiperidin-1-yl)oxyl) or AAT was employed as the
additive working for both charge and discharge processes (amphi-active). The redox-active moiety was rooted in TEMPO,
while the acetamido (AA) functional group inherited the high donor
number (DN) of N,N-dimethylacetamide
(DMAc). Integrating two functional moieties (TEMPO and AA) into a
single molecule resulted in the bifunctionality of AAT (1) facilitating
Li2O2 decomposition by the TEMPO moiety and
(2) encouraging the solvent mechanism of Li2O2 formation by the high-DN AA moiety. Significantly improved LOB performances
were achieved by the superoxide-solvating charge redox mediator, which
were not obtained by a simple cocktail of TEMPO and DMAc
Fire-Inhibiting Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries
Herein,
we present a gel polymer electrolyte (GPE) improving nonflammability
of lithium-ion batteries (LIBs) by blocking radical-initiated chain
reactions which cause thermal runaway and finally fire issues. The
polymer that makes up the nonflammable GPE was (1) soluble in carbonate
electrolytes, (2) cross-linkable in the presence of a popularly used
lithium salt such as LiPF6, (3) gelated only with 2 wt
% in electrolytes, and (4) radical-scavenging by its functional side
chains. Electrolytes having the polymer were thermally gelated within
battery cells after the cells were assembled by a conventional way.
LIB cells with the GPE were durable against external thermal and mechanical
shocks without sacrificing cell performances. The high transference
number of lithium ions and liquid-equivalent ionic conductivity of
the GPE at only 2% solid content having a stable solid-electrolyte
interphase layer formed even improved cell performances at normal
operation conditions
Fire-Inhibiting Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries
Herein,
we present a gel polymer electrolyte (GPE) improving nonflammability
of lithium-ion batteries (LIBs) by blocking radical-initiated chain
reactions which cause thermal runaway and finally fire issues. The
polymer that makes up the nonflammable GPE was (1) soluble in carbonate
electrolytes, (2) cross-linkable in the presence of a popularly used
lithium salt such as LiPF6, (3) gelated only with 2 wt
% in electrolytes, and (4) radical-scavenging by its functional side
chains. Electrolytes having the polymer were thermally gelated within
battery cells after the cells were assembled by a conventional way.
LIB cells with the GPE were durable against external thermal and mechanical
shocks without sacrificing cell performances. The high transference
number of lithium ions and liquid-equivalent ionic conductivity of
the GPE at only 2% solid content having a stable solid-electrolyte
interphase layer formed even improved cell performances at normal
operation conditions