Separators
are key safety components for electrochemical energy storage systems.
However, the intrinsic poor wettability with electrolyte and low thermal
stability of commercial polyolefin separators cannot meet the requirements
of the ever-expanding market for high-power, high-energy, and high-safety
power systems, such as lithium-metal, lithium-sulfur, and lithium-ion
batteries. In this study, scalable bendable networks built with ultralong
silica nanowires (SNs) are developed as stable separators for both
high-safety and high-power lithium-metal batteries. The three-dimensional
porous nature (porosity of 73%) and the polar surface of the obtained
SNs separators endue a much better electrolyte wettability, larger
electrolyte uptake ratio (325%), higher electrolyte retention ratio
(63%), and ∼7 times higher ionic conductivity than that of
commercial polypropylene (PP) separators. Moreover, the pore-rich
structure of the SNs separator can aid in evenly distributing lithium
and, in turn, suppress the uncontrollable growth of lithium dendrites
to a certain degree. Furthermore, the pure inorganic structure endows
the SNs separators with excellent chemical and electrochemical stabilities
even at elevated temperatures, as well as excellent thermal stability
up to 700 °C. This work underpins the utilization of SNs separators
as a rational choice for developing high-performance batteries with
a metallic lithium anode.
To enhance the utilization of sulfur in lithium−sulfur batteries, threedimensional tungsten nitride (WN) mesoporous foam blocks are designed to spatially localize the soluble Li 2 S 6 and Li 2 S 4 within the pore spaces. Meanwhile, the chemisorption behaviors of polysulfides and the capability of WN as an effective confiner are systematically investigated through density functional theory calculations and experimental studies. The theoretical calculations reveal a decrease in chemisorption strength between WN and the soluble polysulfides (Li 2 S 8 > Li 2 S 6 > Li 2 S 4 ), while the interactions between WN and the insoluble Li 2 S 2 /Li 2 S show a high chemisorption strength of ca. 3 eV. Validating theoretical insights through electrochemical measurements further manifest that the assembled battery configurations with sulfur cathode confined in the thickest WN blocks exhibit the best rate capabilities (1090 and 510 mAh g −1 at 0.5C and 5C, respectively) with the highest initial Coulombic efficiency of 90.5%. Moreover, a reversible capacity of 358 mAh g −1 is maintained with a high Coulombic efficiency approaching to 100%, even after 500 cycles at 2C. As guided by in silico design, this work not only provides an effective strategy to improve the retentivity of polysulfides but also underpins that properly architectured WN can be effective retainers of polysulfides.
Microbial
fuel cells (MFCs) are highly appealing for recovering
electricity from organic matter, with the help of electrogenic bacteria.
However, the lack of cost-efficient oxygen reduction reaction (ORR)
catalysts is the main limitation for the performance of MFCs, and
the development of highly electrocatalytic active ORR catalysts for
MFCs remains very challenging. Here, core/shell carbon materials doped
with Co and N (NC@CoNC) are prepared from bimetallic metal–organic
frameworks (MOFs) via a facile pyrolysis method. After being interconnected
by reduced graphene oxide (rGO), this unique NC@CoNC/rGO composite
exhibits excellent electrocatalytic activity when used as the cathode
catalyst in MFCs. The as-fabricated NC@CoNC/rGO catalyst facilitates
favorable four-electron ORR, which can be due to the uniform distribution
of Co nanoparticles, high N content, large surface area, and conductive
graphene framework. Furthermore, the optimized NC@CoNC/rGO achieves
a maximum power density of 2350 mW m–2, which is
even higher than that generated with commercial Pt/C (2002 mW m–2). This work demonstrates that the nonprecious metal
catalyst NC@CoNC/rGO can be considered to be an good alternative in
MFCs.
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