Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes. We report the design of a three-dimensional (3D) holey-graphene/niobia (NbO) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.
Electrochemical
impedance spectroscopy (EIS) consists of plotting
so-called Nyquist plots representing negative of the imaginary versus the real
parts of the complex impedance of individual electrodes or electrochemical
cells. To date, interpretations of Nyquist plots have been based on
physical intuition and/or on the use of equivalent RC circuits. However,
the resulting interpretations are not unique and have often been inconsistent
in the literature. This study aims to provide unequivocal physical
interpretations of electrochemical impedance spectroscopy (EIS) results
for electric double layer capacitor (EDLC) electrodes and devices.
To do so, a physicochemical transport model was used for numerically
reproducing Nyquist plots accounting for (i) electric double layer
(EDL) formation at the electrode/electrolyte interface, (ii) charge
transport in the electrode, and (iii) ion electrodiffusion in binary
and symmetric electrolytes. Typical Nyquist plots of EDLC electrodes
were reproduced numerically for different electrode conductivity and
thickness, electrolyte domain thickness, as well as ion diameter,
diffusion coefficient, and concentrations. The electrode resistance,
electrolyte resistance, and the equilibrium differential capacitance
were identified from Nyquist plots without relying on equivalent RC
circuits. The internal resistance retrieved from the numerically generated
Nyquist plots was comparable to that retrieved from the “IR
drop” in numerically simulated galvanostatic cycling. Furthermore,
EIS simulations were performed for EDLC devices, and similar interpretations
of Nyquist plots were obtained. Finally, these results and interpretations
were confirmed experimentally using EDLC devices consisting of two
identical activated-carbon electrodes in both aqueous and nonaqueous
electrolytes.
The critical role of grain boundaries for (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells studied by Kelvin probe force microscopy under bias voltage and illumination is reported. Ion migration is enhanced at the grain boundaries. Under illumination, the light‐induced potential causes ion migration leading to a rearranged ion distribution. Such a distribution favors photogenerated charge‐carrier collection at the grain boundaries.
The use of solid electrolytes is a promising direction to improve the energy density of lithium‐ion batteries. However, the low ionic conductivity of many solid electrolytes currently hinders the performance of solid‐state batteries. Sulfide solid electrolytes can be processed in a number of forms (glass, glass‐ceramic, and crystalline) and have a wide range of available chemistries. Crystalline sulfide materials demonstrate ionic conductivity on par with those of liquid electrolytes through the utilization of near ideal conduction pathways. Low‐temperature processing is also possible for these materials due to their favorable mechanical properties. The main drawback of sulfide solid electrolytes remains their electrochemical stability, but this can be addressed through compositional tuning or the use of artificial solid electrolyte interphase (SEI). Implementation of sulfide solid electrolytes, with proper treatment for stability, can lead to substantial improvements in solid‐state battery performance leading to significant advancement in electric vehicle technology.
A review on liquid electrolyte design for LIBs operating under low-temperature (<0 °C) conditions. Covers various processes that determine performance below 0 °C and recent literature on electrolyte-based strategies to improve said performance.
This
study aims to provide physical interpretations of electrochemical
impedance spectroscopy (EIS) measurements for redox active electrodes
in a three-electrode configuration. To do so, a physicochemical transport
model was used accounting for (i) reversible redox reactions at the
electrode/electrolyte interface, (ii) charge transport in the electrode,
(iii) ion intercalation into the pseudocapacitive electrode, (iv)
electric double layer formation, and (v) ion electrodiffusion in binary
and symmetric electrolytes. Typical Nyquist plots generated by EIS
of redox active electrodes were reproduced numerically for a wide
range of electrode electrical conductivity, electrolyte thickness,
redox reaction rate constant, and bias potential. The electrode, bulk
electrolyte, charge transfer, and mass transfer resistances could
be unequivocally identified from the Nyquist plots. The electrode
and bulk electrolyte resistances were independent of the bias potential,
while the sum of the charge and mass transfer resistances increased
with increasing bias potential. Finally, these results and interpretation
were confirmed experimentally for LiNi0.6Co0.2Mn0.2O2 and MoS2 electrodes in organic
electrolytes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.