Lithium–sulfur
(Li–S) batteries are regarded as promising
next-generation high energy density storage devices for both portable
electronics and electric vehicles due to their high energy density,
low cost, and environmental friendliness. However, there remain some
issues yet to be fully addressed with the main challenges stemming
from the ionically insulating nature of sulfur and the dissolution
of polysulfides in electrolyte with subsequent parasitic reactions
leading to low sulfur utilization and poor cycle life. The high flammability
of sulfur is another serious safety concern which has hindered its
further application. Herein, an aqueous inorganic polymer, ammonium
polyphosphate (APP), has been developed as a novel multifunctional
binder to address the above issues. The strong binding affinity of
the main chain of APP with lithium polysulfides blocks diffusion of
polysulfide anions and inhibits their shuttling effect. The coupling
of APP with Li ion facilitates ion transfer and promotes the kinetics
of the cathode reaction. Moreover, APP can serve as a flame retardant,
thus significantly reducing the flammability of the sulfur cathode.
In addition, the aqueous characteristic of the binder avoids the use
of toxic organic solvents, thus significantly improving safety. As
a result, a high rate capacity of 520 mAh g–1 at
4 C and excellent cycling stability of ∼0.038% capacity decay
per cycle at 0.5 C for 400 cycles are achieved based on this binder.
This work offers a feasible and effective strategy for employing APP
as an efficient multifunctional binder toward building next-generation
high energy density Li–S batteries.
Heterostructure
engineering is one of the most promising modification
strategies toward improving sluggish kinetics for the anode of sodium
ion batteries (SIBs). Herein, we report a systemic investigation on
the different types of heterostructure interfaces’ effects
of discharging products (Na2O, Na2S, Na2Se) on the rate performance. First-principle calculations
reveal that the Na2S/Na2Se interface possesses
the lowest diffusion energy barrier (0.39 eV) of Na among three kinds
of interface structures (Na2O/Na2S, Na2O/Na2Se, and Na2S/Na2Se) due to
its smallest recorded interface deformation, similar electronegativity,
and lattice constant. The experimental evidence confirms that the
metal sulfide/metal selenide (SnS/SnSe2) hierarchical anode
exhibits outstanding rate performance, where the normalized capacity
at 10 A g–1 compared to 0.1 A g–1 is 45.6%. The proposed design strategy in this work is helpful to
design high rate performance anodes for advanced battery systems.
Sulfur is an attractive cathode material for next-generation lithium batteries due to its high theoretical capacity and low cost. However, dissolution of its lithiated product (lithium polysulfides) into the electrolyte limits the practical application of lithium sulfur batteries. Here we demonstrate that sulfur particles can be hermetically encapsulated by leveraging on the unique properties of two-dimensional materials such as molybdenum disulfide (MoS). The high flexibility and strong van der Waals force in MoS nanoflakes allows effective encapsulation of the sulfur particles and prevent its sublimation during in situ TEM studies. We observe that the lithium diffusivities in the encapsulated sulfur particles are in the order of 10 m s. Composite electrodes made from the MoS-encapsulated sulfur spheres show outstanding electrochemical performance, with an initial capacity of 1660 mAh g and long cycle life of more than 1000 cycles.
Electrocatalysis represents a promising method to generate renewable fuels and chemical feedstock from the carbon dioxide reduction reaction (CO 2 RR). However, traditional electrocatalysts based on transition metals are not efficient enough because of the high overpotential and slow turnover. MXenes, a family of two-dimensional metal carbides and nitrides, have been predicted to be effective in catalyzing CO 2 RR, but a systematic investigation into their catalytic performance is lacking, especially on hydroxyl (−OH)-terminated MXenes relevant in aqueous reaction conditions. In this work, we utilized first-principles simulations to systematically screen and explore the properties of MXenes in catalyzing CO 2 RR to CH 4 from both aspects of thermodynamics and kinetics. Sc 2 C(OH) 2 was found to be the most promising catalyst with the least negative limiting potential of −0.53 V vs RHE. This was achieved through an alternative reaction pathway, where the adsorbed species are stabilized by capturing H atoms from the MXene's OH termination group. New scaling relations, based on the shared H interaction between intermediates and MXenes, were established. Bader charge analyses reveal that catalysts with less electron migration in the *(H)COOH → *CO elementary step exhibit better CO 2 RR performance. This study provides new insights regarding the effect of surface functionalization on the catalytic performance of MXenes to guide future materials design.
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