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.
Highlights
Lithium–sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage
Despite the considerable advantages of Li–S battery, several problems prevent it from practical applications: (1) the insulating characteristic of sulphur and its discharge products (Li2S), leading to a low utilization of active material; (2) large volumetric expansion/shrinkage (80%) during discharge/charge, resulting in an instability of the electrode structure; (3) the soluble intermediates (Li2Sx, 3rxr8) in the organic liquid electrolyte during the cycle process bring about the polysulphide ‘shuttle effect’, which leads to irreversible capacity loss and corrosion on the lithium-metal anode[4,8,9]
To understand the structure and surface modification in improving the performance of N,S-codoped graphene electrode, the cells were disassembled inside the glove box and the surface morphology of the graphene-based sponge cathodes and the lithium metallic anodes after 100 cycles were observed by scanning electron microscopy (SEM)
Summary
Lithium–sulphur batteries with a high theoretical energy density are regarded as promising energy storage devices for electric vehicles and large-scale electricity storage. 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. Despite the considerable advantages of Li–S battery, several problems prevent it from practical applications: (1) the insulating characteristic of sulphur and its discharge products (Li2S), leading to a low utilization of active material; (2) large volumetric expansion/shrinkage (80%) during discharge/charge, resulting in an instability of the electrode structure; (3) the soluble intermediates (Li2Sx, 3rxr8) in the organic liquid electrolyte during the cycle process bring about the polysulphide ‘shuttle effect’, which leads to irreversible capacity loss and corrosion on the lithium-metal anode[4,8,9]. The combination of physical adsorption of lithium polysulphides onto porous graphene and the chemical binding of polysulphides to N and S sites in graphene suppresses sulphur loss during the discharge/charge processes, enabling a high specific capacity of 1,200 mAh g À 1 at 0.2C rate, a high-rate capacity of 430 mAh g À 1 at 2C rate and excellent cycling stability for 500 cycles with nearly 100% Coulombic efficiency for the N,S-codoped graphene electrode
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