Engineering the structure and chemistry of solid electrolyte interface (SEI) on electrode materials is crucial for rechargeable batteries. Using hard carbon (HC) as a platform material, a correlation between Na + storage performance, and the properties of SEI is comprehensively explored. It is found that a "good" SEI layer on HC may not be directly associated with certain kinds of SEI components, such as NaF and Na 2 O. Whereas, arranging nano SEI components with refined structures constructs the foundation of "good" SEI that enables fast Na + storage and interface stability of HC in Na-ion batteries. A layer-by-layer SEI on HC with inorganic-rich inner layer and tolerant organic-rich outer flexible layer can facilitate excellent rate and cycling life. Besides, SEI layer as the gate for Na + from electrolyte to HC electrode can modulate interfacial crystallographic structures of HC with pillar-solvent that function as "pseudo-SEI" for fast and stable Na + storage in optimal 1 m NaPF 6 -TEGDME electrolytes. Such a layer-by-layer SEI combined with a "pseudo-SEI" layer for HC enables an outstanding rate of 192 mAh g −1 at 2 C and stable cycling over 1100 cycles at 0.5 C. This study provides valuable guidance to improve the electrochemical performance of electrode materials through regulation of SEI in optimal electrolytes.
Lithium–sulfur
batteries are the most promising candidates
for advanced electrochemical energy storage systems benefiting from
their high energy density and low cost of sulfur. Improving the conductivity
of sulfur cathode and stabilizing the polysulfide shuttle are the
key factors for obtaining high-performance lithium–sulfur batteries.
Herein, metallic and polar TiB2 nanomaterials are applied
for the first time as sulfur hosts. The 70S/TiB2 composite
exhibits a long-term cycling stability up to 500 cycles at the current
density of 1 C. It is worth noting that even when the sulfur areal
mass loading is up to 3.9 mg cm–2, a stable capacity
of 837 mA h g–1 can be still maintained after 100
cycles. The outstanding electrochemical performance can be attributed
to the strong anchoring effect of TiB2 to lithium polysulfides,
which is confirmed by the X-ray photoelectron spectroscopy analyses
and theoretical calculations with a favorable surface-passivated chemistry.
The study presented here will shed a new light for metal borides as
hosts to improve the cycling life of lithium–sulfur batteries
and provide a deep comprehension of the instinct interaction evolution
at a molecular level, which is invaluable in the material rational
fabrication for future high-performance Li–S batteries.
Although lithium–sulfur batteries have high theoretical energy density of 2600 Wh kg−1, the sluggish redox kinetics of soluble liquid polysulfide intermediates during discharge and charge is one of the main reasons for their limited battery performance. Designing highly efficient electrocatalysts with a core–shell like structure for accelerating polysulfide conversion is vital for the development of Li–S batteries. Herein, core–shell MoSe2@C nanorods are proposed to manipulate electrocatalytic polysulfide redox kinetics, thereby improving the Li–S battery performance. The 1D MoSe2@C is synthesized via a facile hydrothermal and subsequent selenization reaction. The electrocatalysis of MoSe2 is confirmed by the analysis of symmetric batteries, Tafel curves, changes of activation energy, and lithium‐ion diffusion. Density functional theory calculations also prove the low Gibbs free energy of the reaction pathway and the lithium‐ion diffusion barrier. Therefore, the Li–S batteries using MoSe2 electrocatalyst exhibit an excellent rate performance of 560 mAh g−1 at 1 C with a high sulfur loading of 3.4 mg cm−2 and an areal capacity of 4.7 mAh cm−2 at a high sulfur loading of 4.7 mg cm−2 under lean electrolyte conditions. This work provides a deeper insight into regulation of polysulfide redox kinetics in electrocatalysts for Li–S batteries.
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