Computational Insights into the Interaction between Li₂S/Li₂S₂ and Heteroatom‐Doped Graphene Materials

Abstract

Electrochemical nucleation and deposition of Li2S/Li2S2 is among the major problems hindering the application of lithium‐sulfur batteries. Adsorption behavior of Li2Sx (x=1, 2, 4, 8) with nitrogen‐doped, boron‐doped graphene and reduced graphene oxides (r‐GOs) are investigated in this study by DFT method. It is discovered that graphene with pyridinic N doping (PD−N) and pyrrolic N doping (PL−N) are able to benefit the nucleation for short‐chain lithium‐polysulfides (Li2S/Li2S2) through Li−N interaction. r‐GOs can also enhance the nucleation to some extent through Li−O interaction, which is not as good as Li−N interaction. At the same time, pristine graphene, graphene with graphitic N (GRN) and B‐doped graphene can only provide Li−C interaction, which is weaker than Li−O and Li−N. This makes the sequence of adsorption strength to be PD−N≈PL−D>r‐GO>B>GRN≈pristine graphene. The unique mechanism of B‐doped graphene adsorbed with Li2S/Li2S2 is also discovered.

Understanding the role of lithium bonds in doped graphene nanoribbons as cathode hosts for Li‐S batteries: A first‐principles study

“…The charge transfer between the dopants and the adsorbate is further confirmed from the CDD analysis of Li 2 S adsorbed GNRs 22,43 . Figure 3 clearly shows the reduction in the charge density between the regions connecting Li and S of Li 2 S and increase in the charge density between dopant and Li 1 .…”

“…The delocalized π system located in C atoms becomes strengthened due to additional electrons transferred from B atom in the BO‐GNR. Hence, the carbon atoms surrounding the B atom become more active and the substrate becomes more polar causing a more favorable condition for Li 2 S adsorption 22,44 . Hence, it is advantageous to co‐dope GNR with atoms having less electronegativity than carbon along with atoms like oxygen to achieve strong adsorption 45 …”

“…Also, a smaller dopant atomic radius is essential to pair with Li via electrostatic dipole‐dipole interaction 20 . These studies clearly indicate that the dopants act as good traps for LiPS only when they are placed at the edges of graphene nanoribbons (GNRs), with their lone pairs exposed to Li of the incoming LiPS 22 . The same dopants show little or no chemical affinity towards LiPS when they are doped at the basal plane of GNRs.…”

“…20 These studies clearly indicate that the dopants act as good traps for LiPS only when they are placed at the edges of graphene nanoribbons (GNRs), with their lone pairs exposed to Li of the incoming LiPS. 22 The same dopants show little or no chemical affinity towards LiPS when they are doped at the basal plane of GNRs. Another intriguing feature is that the strength of adsorption is not dictated solely by the electronegativity of the dopants, that is, dopants of large electronegativities (eg, Fluorine) do not necessarily have large chemical affinities toward LiPS.…”

A Review of Heteroatom Doped Materials for Advanced Lithium–Sulfur Batteries

“…To further promote the conductivity and adsorption capability for LiPSs, various heteroatom can be doped into the structure of GO or rGO. [ 9,48 ] N‐doped graphene nanosheets ( Figure a) were prepared through the pyrolysis of GO‐cyanamide composite at 900 °C under H 2 /Ar atmosphere. [ 49 ] Cyanamide can not only achieve in situ N doping in graphene as the N source, but also endow graphene with the crumpled morphology.…”