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Long-life Li/polysulphide batteries with high sulphur loading enabled by lightweight three-dimensional nitrogen/sulphur-codoped graphene sponge.

Zhou G, Paek E, Hwang GS, Manthiram A - Nat Commun (2015)

Bottom Line: However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications.The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations.As a result, a high specific capacity of 1,200 mAh g(-1) at 0.2C rate, a high-rate capacity of 430 mAh g(-1) at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Engineering Program &Texas Materials Institute, The University of Texas at Austin, 204 East Dean Keeton Street, Mail Stop: C2200, Austin, Texas 78712, USA.

ABSTRACT
Lithium-sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications. Herein, we present an effective strategy to obtain Li/polysulphide batteries with high-energy density and long-cyclic life using three-dimensional nitrogen/sulphur codoped graphene sponge electrodes. The nitrogen/sulphur codoped graphene sponge electrode provides enough space for a high sulphur loading, facilitates fast charge transfer and better immobilization of polysulphide ions. The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations. As a result, a high specific capacity of 1,200 mAh g(-1) at 0.2C rate, a high-rate capacity of 430 mAh g(-1) at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved.

No MeSH data available.


Related in: MedlinePlus

Theoretical calculations.Optimized configurations for the binding of LiSH to (a) pristine graphene, (b) 1,3-dioxolane, (c–e) S-doped graphene, (f–h) N-doped graphene and (i–k) N,S-codoped graphene. Charge density difference isosurfaces are shown in the insets; the blue and yellow colours indicate the regions of charge gain and loss (of ±0.001 e per bohr3), respectively. Grey, white, blue, yellow, purple and red balls represent C, H, N, S, Li and O atoms, respectively. LiSH binding energies (in eV) and selected bond distances (in Å) are also indicated.
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f6: Theoretical calculations.Optimized configurations for the binding of LiSH to (a) pristine graphene, (b) 1,3-dioxolane, (c–e) S-doped graphene, (f–h) N-doped graphene and (i–k) N,S-codoped graphene. Charge density difference isosurfaces are shown in the insets; the blue and yellow colours indicate the regions of charge gain and loss (of ±0.001 e per bohr3), respectively. Grey, white, blue, yellow, purple and red balls represent C, H, N, S, Li and O atoms, respectively. LiSH binding energies (in eV) and selected bond distances (in Å) are also indicated.

Mentions: To better understand the doping effect, density functional theory (DFT) calculations were performed to examine how the binding strength of the Li–S end of linear lithium polysulphides (Li2Sx) is influenced by the incorporation of N and/or S atoms into the graphene lattice. Here we used a small LiSH molecule to model the Li–S end. This model is simple but should be sufficient enough to demonstrate the influence of doping particularly on the binding interaction of the terminal Li+ cation with a doped graphene sheet, although lithium polysulphides may also exist as complex clusters575859. To confirm whether the H-terminated S will influence the predicted binding strength of the terminal Li+, we also considered Li2S adsorption at a few selected dopant sites, as shown in Supplementary Fig. 12. There are no significant binding energy differences between Li2S and LiSH, implying that it would be reasonable and feasible to use LiSH for the purpose of supporting our experimental observations. For a reference, we first considered the binding of LiSH to a pristine graphene sheet and a 1,3-dioxolane (DOL) molecule, which is widely used for the electrolyte in a Li–S cell. As shown in Fig. 6a, the Li of LiSH is preferentially located at the hollow site above the centre of a hexagon ring with a predicted binding energy of Eb=0.78 eV, in good agreement with the previous DFT results57. Here the Eb is given by ELiSH+EGr−ELiSH/Gr, where ELiSH, EGr and ELiSH/Gr represent the total energies of an isolated LiSH, pristine (or doped) graphene and LiSH adsorbed graphene, respectively. Our calculations also predict that the Li of LiSH can be strongly bound to the O site of DOL with Eb=0.93 eV (Fig. 6b); the larger Eb than that for the graphene case (0.78 eV) may suggest that lithium polysulphides would dissolve into the DOL-based electrolyte instead of adsorbing on the graphene surface, consistent with the existing experimental observations1047.


Long-life Li/polysulphide batteries with high sulphur loading enabled by lightweight three-dimensional nitrogen/sulphur-codoped graphene sponge.

Zhou G, Paek E, Hwang GS, Manthiram A - Nat Commun (2015)

Theoretical calculations.Optimized configurations for the binding of LiSH to (a) pristine graphene, (b) 1,3-dioxolane, (c–e) S-doped graphene, (f–h) N-doped graphene and (i–k) N,S-codoped graphene. Charge density difference isosurfaces are shown in the insets; the blue and yellow colours indicate the regions of charge gain and loss (of ±0.001 e per bohr3), respectively. Grey, white, blue, yellow, purple and red balls represent C, H, N, S, Li and O atoms, respectively. LiSH binding energies (in eV) and selected bond distances (in Å) are also indicated.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4518288&req=5

f6: Theoretical calculations.Optimized configurations for the binding of LiSH to (a) pristine graphene, (b) 1,3-dioxolane, (c–e) S-doped graphene, (f–h) N-doped graphene and (i–k) N,S-codoped graphene. Charge density difference isosurfaces are shown in the insets; the blue and yellow colours indicate the regions of charge gain and loss (of ±0.001 e per bohr3), respectively. Grey, white, blue, yellow, purple and red balls represent C, H, N, S, Li and O atoms, respectively. LiSH binding energies (in eV) and selected bond distances (in Å) are also indicated.
Mentions: To better understand the doping effect, density functional theory (DFT) calculations were performed to examine how the binding strength of the Li–S end of linear lithium polysulphides (Li2Sx) is influenced by the incorporation of N and/or S atoms into the graphene lattice. Here we used a small LiSH molecule to model the Li–S end. This model is simple but should be sufficient enough to demonstrate the influence of doping particularly on the binding interaction of the terminal Li+ cation with a doped graphene sheet, although lithium polysulphides may also exist as complex clusters575859. To confirm whether the H-terminated S will influence the predicted binding strength of the terminal Li+, we also considered Li2S adsorption at a few selected dopant sites, as shown in Supplementary Fig. 12. There are no significant binding energy differences between Li2S and LiSH, implying that it would be reasonable and feasible to use LiSH for the purpose of supporting our experimental observations. For a reference, we first considered the binding of LiSH to a pristine graphene sheet and a 1,3-dioxolane (DOL) molecule, which is widely used for the electrolyte in a Li–S cell. As shown in Fig. 6a, the Li of LiSH is preferentially located at the hollow site above the centre of a hexagon ring with a predicted binding energy of Eb=0.78 eV, in good agreement with the previous DFT results57. Here the Eb is given by ELiSH+EGr−ELiSH/Gr, where ELiSH, EGr and ELiSH/Gr represent the total energies of an isolated LiSH, pristine (or doped) graphene and LiSH adsorbed graphene, respectively. Our calculations also predict that the Li of LiSH can be strongly bound to the O site of DOL with Eb=0.93 eV (Fig. 6b); the larger Eb than that for the graphene case (0.78 eV) may suggest that lithium polysulphides would dissolve into the DOL-based electrolyte instead of adsorbing on the graphene surface, consistent with the existing experimental observations1047.

Bottom Line: However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications.The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations.As a result, a high specific capacity of 1,200 mAh g(-1) at 0.2C rate, a high-rate capacity of 430 mAh g(-1) at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Engineering Program &Texas Materials Institute, The University of Texas at Austin, 204 East Dean Keeton Street, Mail Stop: C2200, Austin, Texas 78712, USA.

ABSTRACT
Lithium-sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. However, the low active material utilization, low sulphur loading and poor cycling stability restrict their practical applications. Herein, we present an effective strategy to obtain Li/polysulphide batteries with high-energy density and long-cyclic life using three-dimensional nitrogen/sulphur codoped graphene sponge electrodes. The nitrogen/sulphur codoped graphene sponge electrode provides enough space for a high sulphur loading, facilitates fast charge transfer and better immobilization of polysulphide ions. The hetero-doped nitrogen/sulphur sites are demonstrated to show strong binding energy and be capable of anchoring polysulphides based on first-principles calculations. As a result, a high specific capacity of 1,200 mAh g(-1) at 0.2C rate, a high-rate capacity of 430 mAh g(-1) at 2C rate and excellent cycling stability for 500 cycles with ∼0.078% capacity decay per cycle are achieved.

No MeSH data available.


Related in: MedlinePlus