Defect‐Rich Hierarchical Porous Mn‐Doped CoP Hollow Microspheres Accelerate Polysulfide Conversion

Abstract

Lithium-sulfur batteries (LSBs) with high theoretical specific capacities have been regarded as the development direction of next generation energy storage. However, the shuttle effect of lithium polysulfides (LiPSs) and the retardation of conversion kinetics have hindered their industrial application. Herein, Mn selectively doped CoP hollow microspheres are designed and synthesized to trap LiPSs and enhance Li-S reaction kinetics. Mn is successfully doped into (100) surfaces of Co 3 O 4 via simple hydrothermal reaction, whereas it is only excessively accumulated on (111) surfaces. The unique selective doping of Mn not only provides an accurate and controllable synthesis path, but also makes synthesized target products rich in phosphorus defects after thermal shock. The adsorption, electrochemical, and in situ XRD and Raman tests prove its enhancement in adsorption capacity for LiPSs and inhibition of shuttle effect. Meanwhile, density functional theory calculations confirm that the reduced reaction energy barriers accelerate the reduction kinetics of sulfur redox conversion. Therefore, the optimal electrode displays an outstanding cycling stability with a capacity fading rate of just 0.0207% per cycle over 1000 cycles at 1 C. This study provides a novel design to promote the practical use of LSBs by introducing lattice defects, enlightening further developments of LSBs.

Deterministic Effect of the Solid-State Diffusion Energy Barrier for a Charge Carrier on the Self-Discharge of Supercapacitors

“…Self-discharge is a significant challenge faced by many high-rate energy storage devices. − While self-discharge is slow and therefore less discussed for lithium-ion batteries (4% per month), it has been identified in nickel–cadmium batteries (20% per month) and nickel–metal hydride batteries (25% per month). It is worth noting that the self-discharge rate of supercapacitors reaches 1.8% per day, which severely limits its application. , Current understanding has attributed the mechanisms of self-discharge for supercapacitors to three processes: Faradaic reactions, charge redistribution, and Ohmic leakage. , The Faradaic reactions are caused by the presence of impurities in the electrolyte that are capable of redox reactions. , Charge redistribution refers to the transfer loss of absorbed charged ions due to the concentration gradient .…”

Improvement of Redox Kinetics of Dendrite-Free Lithium–Sulfur Battery by Bidirectional Catalysis of Cationic Dual-Active Sites

“…Figure d shows the high-resolution fine spectrum of Mn 2p. The peaks at binding energies of 640 and 645 eV corresponded with the 2p 2/3 peaks of Mn 2+ and Mn 3+ , respectively, and the 2p 2/1 peaks corresponded with 654 and 656 eV, respectively Figure e shows deconvoluted peaks at 709, 722 and 711, 725 eV, which corresponded with Fe 2+ and Fe 3+ ions, respectively .…”

“…Compared with the peak of manganese in the 3DCS-MO@C material after adsorption, the peak of the 3DCS-FMO@C material shifted to the direction of low binding energy after Li 2 S 6 adsorption. Thus, 3DCSS-FMO@C had a stronger charge transfer after adsorption and charge transfer from Li 2 S 6 to Mn . The S 2p fine spectrum in Figure c revealed that the terminal sulfur (ST-1) and bridge sulfur (SB0) corresponded with the binding energy positions of 161.1 and 162.7 eV, respectively, and the peak of the 3DCS-FMO@C material moved to the high field after adsorption, indicating that S had undergone a reduction reaction and lost electrons.…”

“…Thus, 3DCSS-FMO@C had a stronger charge transfer after adsorption and charge transfer from Li 2 S 6 to Mn. 30 The S 2p fine spectrum in Figure 8c revealed that the terminal sulfur (ST-1) and bridge sulfur (SB0) corresponded with the binding energy positions of 161.1 and 162.7 eV, respectively, and the peak of the 3DCS-FMO@C material moved to the high field after adsorption, indicating that S had undergone a reduction reaction and lost electrons. The peak at 168.1 eV also corresponded with the generation of high-valent persulfate, verifying the strong interaction between the metal and S 21 and further proving that the 3DCS-FMO@C material had higher adsorption properties for LIPSs.…”

“…The peaks at binding energies of 640 and 645 eV corresponded with the 2p 2/3 peaks of Mn 2+ and Mn 3+ , respectively, and the 2p 2/1 peaks corresponded with 654 and 656 eV, respectively. 30 Figure 3e shows deconvoluted peaks at 709, 722 and 711, 725 eV, which corresponded with Fe 2+ and Fe 3+ ions, respectively. 31 The different peak areas proved that most of the synthesized 3DCS-FMO existed in the forms of Fe 2+ and Mn 2+ , consistent with the XRD data.…”