Electrospinning Equipment: Amorphous Co2P Dual-Functional Fibrous Scaffold for Li-S Batteries

Lithium-sulfur (Li─S) batteries are regarded as one of the most promising energy storage systems due to their high theoretical specific capacity (1675 mAh g−1), low cost, and environmental friendliness. However, the practical application of Li─S batteries has been significantly hindered by the shuttle effect of lithium polysulfides (LiPSs) and the formation of lithium dendrites. Recently, a team led by researchers from the Institute of Functional Nano & Soft Materials at Soochow University, including Zhao Gang, Yan Tianran, Wang Lei, and Yuan Cheng, innovatively designed a porous carbon fiber scaffold embedded with amorphous Co2P (A─Co2P). This scaffold serves as both a cathodic and anodic stabilizer, achieving efficient catalytic conversion of polysulfides and uniform lithium metal deposition in Li─S batteries. This work provides an important reference for the development of high-energy-density and long-cycle-life Li─S batteries. The research findings were published in the top journal in the field of materials science, Advanced Science, under the title "A Bifunctional Fibrous Scaffold Implanted with Amorphous Co₂P as both Cathodic and Anodic Stabilizer for High-Performance Li–S Batteries."

Preparation and Structural Characteristics of Amorphous Co2P

The amorphous Co2P embedded porous carbon fiber scaffold (A─Co2P/PCNF) was prepared via an electrospinning machine and in situ phosphoration. In the experiment, a (Co, Zn)-coordinated zeolitic imidazolate framework (CoZn-ZIF) was first synthesized and then mixed with triphenyl phosphine (PPh3) and polyacrylonitrile (PAN) for electrospinning using a electrospinning device. After high-temperature carbonization and phosphation reactions, the final product was obtained.

Fig 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.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that A─Co2P/PCNF features a three-dimensional interconnected porous structure composed of one-dimensional hierarchical porous nanofibers. High-resolution TEM (HRTEM) images showed that Co2P in A─Co2P/PCNF exhibits disordered atomic distribution without long-range ordered lattice structures, whereas crystalline Co2P (C─Co2P) displays distinct lattice fringes. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analyses further confirmed the unsaturated coordination characteristics of Co atoms and their d-band center close to the Fermi level in amorphous Co2P, which significantly enhanced the adsorption and catalytic ability for LiPSs.

Adsorption and Catalytic Mechanism of Amorphous Co2P on LiPSs

Amorphous Co2P significantly enhanced the adsorption capacity for LiPSs through unsaturated Co sites. Density functional theory (DFT) calculations indicated that the binding energy of A─Co2P to Li2S6 was −3.01 eV, much higher than that of crystalline Co2P (−2.14 eV). This strong interaction originates from the unsaturated Co sites in amorphous Co2P, which strengthen the Co─S bonds and thus weaken the Li─S bonds, effectively suppressing the shuttle effect of LiPSs.

Fig2 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.

Regulation of Li Deposition Behavior by Amorphous Co2P

Amorphous Co2P not only demonstrated excellent catalytic performance in the cathode but also exhibited significant lithiophilic properties in the anode. DFT calculations showed that the binding energy between A─Co2P/PCNF and Li atoms was −0.96 eV, much higher than that of C─Co2P/PCNF (−0.75 eV). 

Fig 3 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.

Full Cell Performance

The full Li─S battery based on A─Co2P/PCNF showed excellent electrochemical performance under high sulfur loading conditions, achieving 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.

Fig 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.

Fig 5 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.

In summary, this study developed a porous carbon fiber membrane loaded with amorphous Co2P (A─Co2P/PCNF) through an electrospinning machine and in situ phosphation, which was used as both a cathodic and anodic stabilizer for high-performance Li─S batteries. This amorphization strategy effectively exposed Co active sites with unsaturated coordination and modulated the d-band center closer to the Fermi level, significantly enhancing the adsorption/catalytic ability for LiPSs and enabling uniform Li deposition while suppressing Li dendrite formation. This work provides a promising strategy for improving the electrochemical performance of Li─S batteries for practical applications by simultaneously enhancing LiPSs retention/catalysis and suppressing Li dendrite growth.

Electrospinning Nanofibers ArticleSource: https://doi.org/10.1002/advs.202501153