Metal–Sulfur Battery Cathodes Based on PAN–Sulfur Composites

Abstract

Sulfur/polyacrylonitrile composites provide a promising route toward cathode materials that overcome multiple, stubborn technical barriers to high-energy, rechargeable lithium-sulfur (Li-S) cells. Using a facile thermal synthesis procedure in which sulfur and polyacrylonitrile (PAN) are the only reactants, we create a family of sulfur/PAN (SPAN) nanocomposites in which sulfur is maintained as S3/S2 during all stages of the redox process. By entrapping these smaller molecular sulfur species in the cathode through covalent bonding to and physical confinement in a conductive host, these materials are shown to completely eliminate polysulfide dissolution and shuttling between lithium anode and sulfur cathode. We also show that, in the absence of any of the usual salt additives required to stabilize the anode in traditional Li-S cells, Li-SPAN cells cycle trouble free and at high Coulombic efficiencies in simple carbonate electrolytes. Electrochemical and spectroscopic analysis of the SPAN cathodes at various stages of charge and discharge further show a full and reversible reduction and oxidation between elemental sulfur and Li-ions in the electrolyte to produce Li2S as the only discharge product over hundreds of cycles of charge and discharge at fixed current densities.

Differences in Electrochemistry between Fibrous SPAN and Fibrous S/C Cathodes Relevant to Cycle Stability and Capacity

“…23,[27][28][29][30] Vice versa, long-chain poly(sulfide)s are soluble in both carbonates and ethers. However, carbonates can react with the dissolved poly(sulfide)s via nucleophilic addition.…”

“…These small amorphous sulfur fragments in ACFs but also the covalently bound oligomeric sulfur units in SPAN should form shortchain but no long chain polysulfides. 29,31 It therefore appeared beneficial to use FEC for both systems, not only to suppress polysulfide shuttle but also to form a stable solid electrolyte interfaces (SEI) on the anode and the cathode. 7,23,28,[31][32][33][34] As can be seen in Figure 2, SPAN gives a high initial capacity of approximately 1370 mA·h·g -1 while S/ACF delivers ca.…”

Structural Design of Lithium–Sulfur Batteries: From Fundamental Research to Practical Application

“…In order to solve the challenge of limited Li + transport, Wang et al [167] introduced F127 and silica species as templates for secondary particles. After the removal of the templates, the interconnected pore network can act as channels for fast Li + transport, resulting in the Li-S batteries assembled with 5 mg cm −2 sulfur-loaded over 1000 cycles [158] Sulfurized polyacrylonitrile 41.8 wt%. c The formation mechanism of phase inversion electrodes and internal ion/electron transport, including ternary phase diagram of phase inversion, schematic illustration of electrode structure, and internal ion/electron transport.…”

Chloride‐Reinforced Carbon Nanofiber Host as Effective Polysulfide Traps in Lithium–Sulfur Batteries

“…Among various alternatives, rechargeable batteries that use earth abundant elements and cost‐effective materials are considered to be promising candidates to meet these performance goals and potentially offer opportunities in large‐scale deployment. In particular, sulfur appeals to the battery community because of its high energy density on both volume (2.8 kWh L −1 ) and weight (2.5 kWh kg −1 ) basis 7, 8, 9, 10. Unlike the widespread LIBs that host lithium in its ionic state and generally yield fewer than one electron per metal atom, a lithium–sulfur battery achieves its high energy (theoretical capacity of 1675 mAh g −1 ) from the multi‐step electrochemical redox reactions by bonding to two Li ions non‐topotactically (S 8 + 16Li ↔ 8Li 2 S) and offer up to two electrons per sulfur atom.…”

“…Cathode modification is a common method to effectively sequester LiPS by incorporating affinity additives. Graphene oxide,16, 17 metal oxides/sulfides,18, 19, 20, 21 polymers,9, 22, 23 and bifunctional binders24, 25 have been widely studied to constrain active cathode materials by the high binding energy between sulfur species and O,N‐containing functional groups. These studies have indicated that stronger interactions between the polar group from the conductive materials (e.g., oxides and sulfides) and the S species enable better confinement of Li 2 S x and enhance the cycling performance of an Li–S cell.…”