Synthesis of Free‐Standing Co_xP/Co₃(PO₄)₂/C Composite Nanofiber Mats and Their Characteristics as Multi‐functional Interlayers for Lithium‐Sulfur Batteries

Abstract

The free‐standing cobalt phosphides‐based composite nanofiber mats with different compositions (CoyP/C, CoxP/Co3(PO4)2/C, where 2>x>y>1) were synthesized by electrospinning with heat treatments and applied as multi‐functional interlayers for lithium‐sulfur batteries. The polysulfide confining ability of the interlayers was evaluated by a static polysulfide adsorption test and an electrochemical conversion test using symmetric cells. The CoxP/Co3(PO4)2/C exhibited better catalytic performance for converting polysulfides, owing to the combination of CoxP with Co3(PO4)2 and P‐doped carbon. As a result, the lithium‐sulfur cell with this interlayer delivered a high initial discharge capacity of 1483 mAh g−1 at 0.1 C, retaining 705 mAh g−1 after 200 cycles at 0.5 C with 100 % Coulombic efficiency. The polysulfide trapping by the interlayer was further elucidated from the results of its ex situ characterizations after discharge and charge processes at different cycles in lithium‐sulfur cells.

A review on electrospun polyvinylpyrrolidone-derived carbon composite nanofibers as advanced functional materials for energy storage applications and beyond

“…64 On the other hand, these reducing properties of PVP could be efficiently utilized in the reduction of SnO 2 nanoparticles forming metallic Sn particles, 65 SnO x within porous carbon nanobers, 66 or reduction of threevalent Fe species into two-valent Fe, 67 preparation of graphene from graphene oxide, 59 and reducing phosphates to phosphides. 68 PVP is soluble in many solvents, but EthOH and distilled water are the most commonly used alone or in combination as they are comparably green. However, DMF and isopropanol (i-PrOH) are sometimes also used.…”

“…88 However, when synthesizing more complex oxygen-rich compounds, utilizing oxygen-free precursors (with weak oxidizing properties), or aiming for lower carbon contents, a pre-oxidation step is required. 44,61,68 According to Kim et al, atomic reorganization of PVP starts at 210 °C, combustion of PVP occurs in the O 2 atmosphere at 290 °C and thermal decomposition of the polymer starts at 350 °C. 73 Hieu et al and Szilágyi et al concluded that complete thermal decomposition of PVP approximately occurs at 450 °C.…”

“…The designed interlayers catalyze the further electrochemical conversion of polysuldes and allow the efficient utilization of the active material. 68,92 The insertion of the PVP-derived free-standing interlayer has been proven effective not only in lithium-sulfur batteries but also in lithium batteries with other sulfur-based cathode materials, such as S-rich CuS. 134 The insertion of the carbon ber paper as an interlayer stabilized the uctuating charge capacity by preventing the shuttle of lithium polysuldes.…”

“…64 On the other hand, these reducing properties of PVP could be efficiently utilized in the reduction of SnO 2 nanoparticles forming metallic Sn particles, 65 SnO x within porous carbon nanofibers, 66 or reduction of three-valent Fe species into two-valent Fe, 67 preparation of graphene from graphene oxide, 59 and reducing phosphates to phosphides. 68…”

“…The designed interlayers catalyze the further electrochemical conversion of polysulfides and allow the efficient utilization of the active material. 68,92…”