Lithium-sulfur batteries' high theoretical energy density and affordability make them excellent devices for storing electrochemical energy. The primary issues that lithium-sulfur batteries encounter are capacity degradation and slow electrode reaction kinetics.
Study: ZnS-Nanoparticle-Coated Carbon Cloth as an Efficient Interlayer for High-Performance Li–S Batteries. Image Credit: Veleri/Shutterstock.com
A paper published in the journal ACS Applied Energy Materials reported using a single-pot hydrothermal process to synthesize zinc sulfide nanoparticle catalysts and support them on a fine carbon cloth nanolayer for stabilizing the electrochemistry of lithium-sulfur batteries.
Lithium-Sulfur Batteries – The Future of Energy Storage
Lithium-sulfur batteries possess excellent energy density and specific capacity and have therefore piqued the attention of researchers. These batteries are eco-friendly and inexpensive, which makes them ideal candidates for use in large-scale electrochemical energy storage and in electric vehicles.
The non-toxic nature, accessibility, and high theoretical capacity of sulfur make it an appealing option for the anode in lithium-sulfur batteries.
Current Challenges in Using Lithium-Sulfur Batteries
Multiple key issues prevent the practical application of lithium-sulfur batteries. Sulfur exhibits poor bulk conductivity and significant volumetric changes during lithiation and delithiation processes.
While decreasing the size of sulfur particles to the nanometer scale may improve charge transport and reduce volumetric changes during the release or uptake of lithium, lithium-sulfur batteries still face other issues.
The lithium-sulfur conversion process produces higher-order intermediates of lithium polysulfide (LiPS), which exhibit high solubility in organic electrolytes. These intermediates are then either oxidized back to sulfur or reduced to lower-order polysulfides.
The dissolved sulfur species tend to shuttle towards the passivated lithium anode, resulting in a permanent depletion of active sulfur from the cathode.
Using sulfur nanoparticles increases the contact area between the electrolyte and sulfur, which may exacerbate the shuttling process of lithium polysulfides. Therefore, lithium-sulfur batteries often exhibit poor cycle performance and Coulombic efficiency.
Addressing the Shuttling of Lithium Polysulfides
The LIPS shuttling phenomenon could be prevented by inserting a functional carbon nanolayer at the cathode side, which would translate to increased energy storage performance of the lithium-sulfur battery.
Carbon nanolayers having appropriate porosity lead to better adsorption of the higher order lithium polysulfides during battery use. The excellent electrical conductivity of carbon compensates for the weak electrical conductivity of sulfur species and reduces resistance to charge transmission at the electrolyte-cathode interface.
The non-polar carbon, unfortunately exhibits poor chemical engagement with the polar lithium polysulfides.
Existing studies have explored the use of metallic catalysts, including the oxides, carbides, nitrides, and sulfides of metals, for enhancing the interaction of lithium polysulfide with the host and facilitating the redox process.
Pros and Cons of Using Zinc Sulfide
Sulfides of metals have received a lot of attention because of their strong affinity for lithium polysulfides and their inexpensive nature.
Zinc sulfide (ZnS) has shown good potential as a catalyst because of its ability to boost lithium polysulfide redox reaction kinetics. ZnS has a strong affinity for lithium polysulfides and allows for a smaller surface diffusion energy for lithium polysulfides.
Nonetheless, zinc sulfide has poor bulk electrical conductivity, and introducing too much sulfide into the sulfur cathode impedes charge transfer and reduces the practical capacity of the cathode.
What Did the Researchers Do?
In this study, the team demonstrated that depositing zinc sulfide nanoparticles upon a conducting carbon cloth (ZnS@CC) nanolayer, rather than directly applying it on the cathode, effectively increased the performance of lithium-sulfide batteries.
The conducting carbon cloth nanolayer functioned as a barrier to the shuttling of lithium polysulfides and provided additional electron transport routes as well.
The zinc sulfide nanoparticles aided in the chemical adsorption of lithium polysulfides and catalyzed the redox process.
Results of the Study
The team showcased a multifunctional ZnS@CC nanolayer for lithium-sulfur batteries. A facile single-pot hydrothermal process was used, and the zinc sulfide mass ratio was considerably lowered by depositing the nanoparticle catalyst onto the conducting framework.
Zinc sulfide nanoparticles were crucial for adsorption of the migrating lithium polysulfides and catalysis of the redox reactions, while the carbon cloth nanolayer improved the overall electrical conductivity.
Density functional theory simulations demonstrated that the high polysulfide adsorption energy and low lithium-ion diffusion barrier on zinc sulfide minimized polysulfide shuttling and enhanced the redox reactions.
After 100 cycles, the sulfur cathode with the ZnS@CC nanolayer retained over 93% of its capacity.
The methodical design approach of the ZnS@CC nanolayer represents a facile method for minimizing the required number of catalysts for future applications of lithium-sulfur batteries.
Liu, R., Tao, W. et al. (2022). ZnS-Nanoparticle-Coated Carbon Cloth as an Efficient Interlayer for High-Performance Li–S Batteries. ACS Applied Energy Materials. Available at: https://pubs.acs.org/doi/10.1021/acsaem.2c02021