A Bifunctional Fibrous Scaffold Implanted with Amorphous Co2P as both Cathodic and Anodic Stabilizer for High-Performance Li─S Batteries

Abstract

The shuttling of lithium polysulfides (LiPSs) and the formation of lithium dendrites have substantially impeded the practical application of lithium-sulfur (Li─S) batteries. To simultaneously solve these issues, a porous carbon fibrous scaffold embedded with amorphous Co₂P (A─Co₂P) is designed as both a cathodic and anodic stabilizer to construct high-rate and long-life Li─S batteries. The meticulously designed self-supporting membrane with an integrated carbon network and porous structure offers superior conductivity and copious spaces for uniform Li₂S precipitation in the cathode and Li deposition in the anode. Moreover, the incorporated A─Co₂P provides abundant unsaturated sites, which can not only facilitate the exposure of active sites but also modulate the electronic configuration for enhanced LiPSs adsorption and catalysis capability. Concurrently, the presence of lithiophilic A─Co₂P sites also reinforces the stability of Li anode with the suppressed formation of dendrites. The constructed full Li─S batteries deliver a high areal capacity of 6.6 mAh cm^-2 with a sulfur loading of 8.5 mg cm^-2 and a low capacity decay rate of 0.047% per cycle after 800 cycles. This work provides a simple yet effective strategy to construct practical Li─S batteries by simultaneously addressing LiPSs shuttling and Li dendrite growth.

Keywords: Li dendrites; Li–S batteries; amorphous structure; catalytic conversion; shuttle effect.

Figure 1

a) Schematic illustration of the synthetic procedure of A─Co₂P/PCNF. b) SEM image of A─Co₂P/PCNF. c) TEM image of A─Co₂P/PCNF. d,e) HAADF‐STEM image and corresponding elemental mapping images of A─Co₂P/PCNF. f) HRTEM image of A─Co₂P/PCNF. g) HRTEM image of C─Co₂P/PCNF. h) XRD patterns of A─Co₂P/PCNF and C─Co₂P/PCNF.

Figure 2

a) P 2p and b) Co 2p XPS spectra of A─Co₂P/PCNF and C─Co₂P/PCNF. c) Co K‐edge XANES spectra and d) FT‐EXAFS spectra of A─Co₂P/PCNF and C─Co₂P/PCNF. EXAFS fitting curves in k‐space and R‐space of e) A─Co₂P/PCNF and f) C─Co₂P/PCNF. WT‐EXAFS plots of g) A─Co₂P/PCNF and h) C─Co₂P/PCNF. i) Schematic illustration of crystal structures for A─Co₂P/PCNF and C─Co₂P/PCNF.

Figure 3

a) Spider chart of adsorption information of Li₂S₆ on A─Co₂P and C─Co₂P. b) Charge density differences of A─Co₂P‐Li₂S₆ and C─Co₂P‐Li₂S₆. The yellow region represents charge gain while the cyan region corresponds to charge loss. c) Co 3d PDOS of A─Co₂P and C─Co₂P. d) CV curves and e) EIS spectra of Li₂S₆ symmetric cells with different electrodes. f) CV curves of different electrodes. g) Li₂S deposition and h) Li₂S dissolution profiles.

Figure 4

a) EIS spectra of different cathodes. b) Cycling performances and c) corresponding charge/discharge profiles. d) Rate performances. e) Charge/discharge profiles of A─Co₂P/PCNF cathode at different rates. f) Discharge capacity from high plateau (denoted as Q₁) and low plateau (denoted as Q₂) at different rates. g) Cycling performance of A─Co₂P/PCNF cathode with high sulfur loadings at 0.1 C. h) Long‐term cycling stability of A─Co₂P/PCNF cathode at 1 C.

Figure 5

a) Binding energy of Li atom with A─Co₂P/PCNF and C─Co₂P/PCNF. Charge density difference patterns of b) A─Co₂P/PCNF‐Li and c) C─Co₂P/PCNF‐Li. d) Schematic illustration of Li deposition on bare Li and corresponding COMSOL simulations of e) current density distribution and f) Li⁺ flux. g) Schematic illustration of Li deposition on A─Co₂P/PCNF‐Li and corresponding COMSOL simulations of h) current density distribution and i) Li⁺ flux. The color shift from red to blue corresponds to a change of electric field strength or Li concentration from high to low degree.

Figure 6

a) Schematic illustration of Li deposition on A─Co₂P/PCNF. b) Voltage profiles of Li plating/stripping on different substrates at a current density of 1.0 mA cm⁻² with a capacity of 1.0 mAh cm⁻². c) CE at a current density of 1.0 mA cm⁻² with a capacity of 1.0 mAh cm⁻². d) SEM images of A─Co₂P/PCNF deposited with different amount of Li. e) Galvanostatic cycling of symmetric cells at a current density of 1.0 mA cm⁻² with a capacity of 1.0 mAh cm⁻² and f) enlarged profiles at different cycles. g) Rate performances of symmetric cells with a fixed capacity of 1.0 mAh cm⁻².

Figure 7

a) Schematic illustration of A─Co₂P/PCNF dual‐functional fibrous scaffold‐enabled Li−S full batteries. b) CE profiles with bare Li and A─Co₂P/PCNF‐Li. c) Long‐term cycling stability of Li−S full batteries. d) Charge/discharge profiles and e) cycling performance of Li−S full batteries with high sulfur loadings at 0.1 C. f) Spider chart of electrochemical performances enabled by A─Co₂P/PCNF dual‐functional fibrous scaffold in comparison with the recently reported dual‐functional Li−S batteries.