Stable cycling of lithium sulfide cathodes through strong affinity with multifunctional binders

Rechargeable lithium sulfur batteries have attracted great interest in recent years because of their high theoretical specific energy, which is several times that of current lithium-ion batteries. Compared to sulfur, fully-lithiated Li₂S represents a more attractive cathode material because it enables pairing with safer, lithium metal-free anodes.

Stanford researchers have designed and tested a new framework for a rational design of stable and high performance Li₂S cathodes by using ab initio simulations to elucidate the interaction between Li₂S and lithium polysulfides with various functional groups found in macromolecular binders. Using polyvinylpyrrolidone (PVP) as a binder in one embodiment, an initial specific capacity of about 760 mAh g^-1 of Li₂S (~1,090 mAh g^-1 of S) was achieved at 0.2C, with unprecedented capacity retention of about 94% in the first 100 cycles. Even after prolonged cycling over 500 charge/discharge cycles, cells retained about 69% of their initial capacity, which corresponds to a small capacity decay of about 0.062% per cycle.

Figure 1

Figure 1 description -(a, b) Ab initio simulations showing the most stable configuration and calculated binding energies of Li₂S and Li–S• species with (a) PVP and (b) PVDF binders. (c and d) Optical microscopy and digital camera images (inset) showing the electrode slurry of (c) Li₂S /carbon black/PVP binder and (d) Li₂S /carbon black/PVDF binder in N-methyl 2-pyrrolidinone (60:35:5 by weight in both cases) (e) Specific capacity and Coulombic efficiency of Li₂S cathodes using PVP binder upon prolonged cycling over 500 cycles at 0.2 C.

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