Atomically distributed asymmetrical five-coordinated Co–N₅ moieties on N-rich doped C enabling enhanced redox kinetics for advanced Li–S batteries

Abstract

Lithium-sulfur (Li-S) batteries show great promise to serve as high-energy-density energy storage devices. Nevertheless, the practical applications of Li-S batteries are significantly limited by the shuttle effect and sluggish sulfur...

Enhancing Sulfur Redox Conversion of Active Iron Sites by Modulation of Electronic Density for Advanced Lithium‐Sulfur Battery

“…Additionally, two peaks at 168.6 and 169.2 eV belonging to the thiosulfate and sulfate species could be observed, indicating a strong interaction between Fe‐NPPC and LiPSs (Figure 5e). [ 37,39,40 ] Similarly, a shift toward higher binding energy was also generated in the high‐resolution P 2p XPS spectrum, implying the chemical affinity between the P atom in Fe‐NPPC and LiPSs (Figure S22b, Supporting Information). In addition, the high‐resolution Li 1s XPS spectrum can be divided into two typical peaks located at 56.3 and 58.2 eV, respectively, which are attributed to the formation of Li‐S and Li‐N bonds resulting from the strong adsorption between Fe‐NPPC and LiPSs (Figure 5f).…”

“…[34,35] However, compared with FePc and FePc/PC, the reduced peak intensity implies that the symmetry of Fe-NPPC is weakened and further confirms the strong charge transfer from the Fe site. [36,37] Extended X-ray absorption fine structure (EX-AFS) was employed to analyze the coordination configuration of Fe sites in Fe-NPPC. A typical peak at 1.47 Å was observed from the Fourier-transformed EXAFS (FT-EXAFS) spectrum in the R space (Figure 3c), which can be attributed to the Fe-N scattering path.…”

“…As shown in Figure a, the Fe‐NPPC‐based cell exhibits two reduction peaks and two overlapped oxidation peaks, corresponding to the invertible multiphase conversion reaction (S 8 ↔ LiPSs ↔ Li 2 S/Li 2 S 2 ). [ 8,9,37 ] Notably, the Li‐S cell with Fe‐NPPC modified separator presents the largest peak current densities and the smallest peak potential gaps (Gap A for oxidation peak and Gap B for reduction peak) among the cells with the PP and modified separators, suggesting the best SROR kinetics and reduction of polarization in the Fe‐NPPC‐based cell (Figure 5b). Moreover, the Tafel plots of the reduction at about 2.3 and 2.0 V denoted as R −2.3 V and R −2.0 V and oxidation at about 2.4 V denoted as O −2.4 V processes were also surveyed to well evaluate the catalytic activities in the Li‐S batteries.…”

“…The Li‐ion diffusion kinetics of the cell was investigated by CV measurements with different sweep rates from 0.2 to 0.5 mV (Figure S20, Supporting Information). The cathodic and anodic peak (A, B, and C) current densities appear a linear relationship with the square root of sweep rates in terms of the Randles–Sevick equation (Equation (S2), Supporting Information), [ 37 ] therefore, the slope appears a proportional relationship with the Li‐ion diffusion coefficient (D Li+ ) (Figure S21, Supporting Information). Obviously, the slope of cells based on the Fe‐NPPC catalyst at peaks A, B, and C display the highest value among the various cells, reflecting an outstanding Li‐ion diffusion in the Li‐S battery equipped with the Fe‐NPPC catalyst functionalized separator.…”

Single-atom site catalysis in Li–S batteries

“…In another work, Wang et al confined Fe(AcAc) 3 into ZIF-8. 130 The evaporation of Zn during the thermal decomposition process produced a large amount of unsaturated N, which stabilized the Fe atoms by coordinating with them. Metal phthalocyanine compounds have well-defined M–N 4 coordination structures, making them suitable precursors for preparing SASCs.…”