Magnetic Control of Electrolyte Trapping Polysulfide for Enhanced Lithium-Sulfur Batteries

Abstract

Lithium sulfur (Li-S) batteries are considered one of the most promising energy storage devices due to their high specific capacity, pollution-free reactant, and low cost. However, the “shuttle effect” of lithium polysulfide (Li2S x ) leads to a fast capacity decay and poor cycle life. Here, the magnetorheological effect (MRE) is first applied in Li-S batteries and a magnetic control electrolyte is designed by introducing carbonyl iron powders (CIPs) to improve the performance of Li-S batteries. According to adsorption bonding theory, the binding energy of Fe site with Li2S4 is up to 2.68 eV via discrete Fourier transform (DFT) calculation. After coupling an external magnetic field, the uniform distribution of CIPs avoids the accumulation on the cathode surface. The induced magnetic field of spherical particles captures dissolved S x 2− effectively by Lorenz force, which is confirmed by adsorption experiments. These magnetized particles form a magnetic shield layer in the electrolyte and alleviate the “shuttle effect.” At 0.2 C, the initial specific capacity reaches 1296 mAh g−1. Magnetic control electrolyte provides not only a novel insight but also creates a new possibility for mitigating the “shuttle effect” thereby promoting performance of Li-S batteries.

External field–assisted batteries toward performance improvement

“…47 However, the introduction of magnetic-field into rechargeable batteries has recently become an attractive topic for boosting battery performance. Although some achievements have been made, for example, dendrite formation inhibition 18,19,21 and polysulfide shuttle effect mitigation, 48,49 the battery reaction mechanism and long-term stability under the coexistence of battery electric field and magnetic field have yet to be thoroughly studied and understood. An in-depth understanding of magnetic field effects and the challenges can lead to significant technological breakthroughs in magnetic field-assisted batteries.…”

“…50 The MHD effect can promote the battery mass transfer process and facilitate the uniform shape of deposited morphology, thereby benefiting the battery performance with much-improved energy efficiency, capacity, and cycling stability. It is worth noting that in the reported magnetic field-assisted sulfur-based systems, 48,49,51 magnetic particles, such as Fe 2 O 3 and carbonyl iron, are typically used (Figure 3B). These magnetic particles, containing vacant electron d-orbital Fe atom, can form strong bonds with polysulfide species.…”

“…48 Recently, soft magnetic particles carbonyl iron powders (Fe(CO) 5 ) with dual effects of chemical adsorption and response to the magnetic field were introduced to Li-S batteries. 49 In the presence of an external magnetic field, these soft magnetic particles added to the cathode side could be raised into the electrolyte by the Lorentz force and trap the polysulfide around themselves, leading to a limited dissolution of polysulfide in the electrolyte and alleviating the shuttle effect. 48 Compared with the condition without an external magnetic field, the battery performance, especially CE and specific capacity, can be markedly improved.…”

“…When an external magnetic field was applied, these superparamagnetic γ‐Fe 2 O 3 nanoparticles can be attracted to the magnetic field and make polysulfide concentrated close to the current collector, thus leading to the high utilization of polysulfide, minimal shuttle effect, and enhanced capacity in the battery 48 . Recently, soft magnetic particles carbonyl iron powders (Fe(CO) 5 ) with dual effects of chemical adsorption and response to the magnetic field were introduced to Li–S batteries 49 . In the presence of an external magnetic field, these soft magnetic particles added to the cathode side could be raised into the electrolyte by the Lorentz force and trap the polysulfide around themselves, leading to a limited dissolution of polysulfide in the electrolyte and alleviating the shuttle effect 48 .…”

Separator Modified by Carbon-Encapsulated CoFe Alloy Nanoparticles Supported on Carbon Nanotubes for Advanced Lithium–Sulfur Batteries

“…Pan et al reported that the adsorption free energy of H atoms (Δ G H* ) of bimetallic CoFe@N–C (−0.561 eV) is lower than that of Fe@N–C (−0.603 eV) and Co@N–C (−0.623 eV), which justifies the improvement in the HER activity . Previous works have demonstrated that the adsorption energy between lithium polysulfides (Li 2 S 4 ) and CoFe is −17.63 eV by DFT, which is much higher than that of single metals Co (−3.11 eV) and Fe (−2.68 eV) and other Co-based metallic alloys (CoNi: −4.24 eV). − …”