Precise Synthesis of Fe-N₂ Sites with High Activity and Stability for Long-Life Lithium–Sulfur Batteries

Abstract

Precisely tuning the coordination environment of the metal center and further maximizing the activity of transition metal–nitrogen carbon (M-NC) catalysts for high-performance lithium–sulfur batteries are greatly desired. Herein, we construct an Fe-NC material with uniform and stable Fe-N2 coordination structure. The theoretical and experimental results indicate that the unsaturated Fe-N2 center can act as a multifunctional site for anchoring lithium polysulfides (LiPSs), accelerating the redox conversion of LiPSs and reducing the reaction energy barrier of Li2S decomposition. Consequently, the batteries based on a porous carbon nitride supported Fe-N2 site (Fe-N2/CN) host exhibit excellent cycling performance with a capacity decay of 0.011% per cycle at 2 C after 2000 cycles. This work deepens the understanding of the relationship between electronic structure of M-NC sites and the catalysis effect for the conversion of LiPSs. This strategy also provides a potent guidance for the further application of M-NC materials in advanced lithium–sulfur batteries.

Crystal Facet Engineering Induced Active Tin Dioxide Nanocatalysts for Highly Stable Lithium–Sulfur Batteries

“…The more negative binding energy between SnO 2 (332) plane and Li 2 S implies the stronger interaction, which is conducive to the uniform deposition of Li 2 S and mutual electron transfer. [ 32 ] Moreover, the bond length of LiS on SnO 2 (332) crystal face is stretched to 2.407 Å (Figure 3b), which is significantly longer than those on SnO 2 (111) crystal face (2.308 Å) and in the original Li 2 S (2.099 Å, Figure S14b, Supporting Information). These calculation results indicate that high‐index SnO 2 (332) facets could more efficiently weaken the binding between Li and S, thereby accelerating the breaking of LiS bonds.…”

“…[ 31 ] Obviously, the discharge capacities at the high voltage plateau (Q 1 ) and low voltage plateau (Q 2 ) of SnO 2 {332}‐G cell are both higher than those of SnO 2 {111}‐G cell and G cell. Moreover, the calculated capacity ratio of Q 2 to Q 1 (Q 2 /Q 1 ) of SnO 2 {332}‐G cell is larger compared to SnO 2 {111}‐G cell and G cell, which manifests the superiority of SnO 2 {332}‐G in suppressing the shuttling of LiPSs and its stronger catalytic effect in promoting the conversion of LiPSs to unsolvable Li 2 S. [ 32 ] In comparison with SnO 2 {111}‐G cell and G cell, SnO 2 {332}‐G cell exhibits a smaller polarization (∆ E 1 = 0.1634 V), which further verifies the enhanced electrochemical kinetics stemming from SnO 2 {332}‐G. Particularly, the initial charge potential barrier of SnO 2 {332}‐G cell is much lower than the other two cells (Figure 5c), which implies that SnO 2 {332}‐G with high‐index facets has the strongest catalytic effect on the decomposition of Li 2 S.…”

High‐Capacity and Stable Sodium‐Sulfur Battery Enabled by Confined Electrocatalytic Polysulfides Full Conversion

“…[ 21 ] Further, the initial charging period was highlighted, the lower overpotential suggests the confined electrocatalytic FC‐PPy center could lower the Na 2 S activation energy barrier and the electrodeposited Na 2 S have much higher electrochemical activity. [ 13,22 ] As compared in Figure S4, Supporting Information, it is evident that the capacity increase of sulfur cathodes with varied carbon substrates was mainly contributed by sulfur redox process and strong interaction of active component with the doped functional sheath. The capacitive and pseudocapacitive contributions of CFC and CFC@FC‐PPy were 35.8 and 79.5 mAh g −1 at 100 mA g −1 , respectively, and 20.7 and 67.3 mAh g −1 at 1000 mA g −1 .…”

High-Index Faceted Nanocrystals as Highly Efficient Bifunctional Electrocatalysts for High-Performance Lithium–Sulfur Batteries

“…2 a–c). The binding energies ( E b ) between different exposed crystal facets of two kinds Fe 2 O 3 and Li 2 S 4 were remarkably different, calculated via a formula ( E b = E Li2S4 + crystal facet − E crystal facet − E Li2S4 ) [ 59 ]. The binding energy values of Li 2 S 4 on the (13 4) and (12 8) facets of C-Fe 2 O 3 were − 1.50 and −1.18 eV, which were more negative than on the (01 2) facets of P-Fe 2 O 3 ( − 0.82 eV).…”