Controllable synthesis of sulfurized polyacrylonitrile nanofibers for high performance lithium–sulfur batteries

Sulfurized Polyacrylonitrile (SPAN): Changes in Mechanical Properties during Electrochemical Lithiation

“…First, we create a carbonized PAN (c-PAN) structure followed by a sulfurization procedure to obtain the SPAN structure, and finally, we model the SPAN lithiation (Li-SPAN). This simulation procedure for the SPAN synthesis emulates a two-step SPAN synthesis procedure similar to experiments where the PAN dehydrogenation precedes the sulfurization process. , …”

“…The sulfurized polyacrylonitrile (SPAN) is a low-cost composite material that constitutes itself as a game changer for lithium–sulfur (Li–S) batteriesone of the most promising electrochemical systems to replace current Li-ion batteries in high-energy density applications. − The SPAN material enhances the low sulfur electronic conductivity, suppresses lithium–polysulfides (Li-PSs) dissolution during cycling, and has the potential to deliver specific energy close to ∼1176 W h kg –1 assuming complete reaction to Li 2 S. − The SPAN material differentiates from other sulfur–carbon composites because of the covalent C–S bonding produced after high-temperature PAN pyrolyzation with sulfur. − The covalent interaction between sulfur and the graphitized carbon skeleton changes the sulfur aggregation from its typical eight-membered crown ring orthorhombic configuration to a short-length sulfur chains distribution (−S x –, x ≤ 4). The SPAN material’s complex structural features induce a single plateau and a slightly sloped voltage discharge profile centered at 1.7 V vs Li/Li + , , deviated from the typical two-sloped discharge profile found in elemental sulfur .…”

“…The ReaxFF potential is particularly well suited for modeling fracture because of its ability to treat covalent bond cleavage events that evolve into local stress concentrations and crack growth . We first create a representative model for lithiated SPAN following a sequential simulation protocol that emulates a sequential synthesis procedure where the PAN carbonization precedes the sulfurization and subsequent lithiation. , We measure the main structural features before lithiation in terms of the skeleton’s graphitization degree and sulfur aggregation state. We proceed to evaluate the volume expansion, Young’s modulus (YM), yield strength, and ultimate tensile strength (UTS) with increasing lithium contents.…”

“…This simulation procedure for the SPAN synthesis emulates a two-step SPAN synthesis procedure similar to experiments where the PAN dehydrogenation precedes the sulfurization process. 4,8 For the carbonization step, Figure 1 shows 48 idealized ladder PAN structures with four repetitive units each, packed randomly to a 1.6 g/cm 3 density 28 within a cubic simulation cell (30 Å × 20 Å × 20 Å) with periodic boundary conditions along the x-, y-, and z-coordinates. Earlier carbon fiber's carbonization simulations with PAN/graphene show that the polymer chains' initial alignment affects neither the all-carbon ring formation dynamics nor the gas byproduct production.…”

Geometrical engineering of a SPAN–graphene composite cathode for practical Li–S batteries

“…SPAN has become a popular cathode because of its outstanding properties such as nearly nonexistent LiPs dissolution, improved conductivity and single-plateau behavior, which leads to an improved rate capacity and cycling ability. 7,[28][29][30][31][32][33][34] Unsatisfactory conductivity has mostly been resolved through the addition of highly conductive nanocarbon materials such as graphene, carbon nanotubes, and porous carbon. [32][33][34][35][36][37][38][39][40] Importantly, SPAN materials have the ability to maintain superior sulfur utilization (approximately 96.5%) during long-term cycling.…”