2 research outputs found
Sulfur-Functionalized Mesoporous Carbons as Sulfur Hosts in Li–S Batteries: Increasing the Affinity of Polysulfide Intermediates to Enhance Performance
The Li–S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g<sup>–1</sup> and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S<sub>8</sub>, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S–MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S–MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60–100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S–MC materials, which is the likely cause for enhanced cyclability
Nanostructured Mn-Doped V<sub>2</sub>O<sub>5</sub> Cathode Material Fabricated from Layered Vanadium Jarosite
We
propose a nanostructured Mn-doped V<sub>2</sub>O<sub>5</sub> lithium-ion
battery cathode material that facilitates cathodic charge
transport. The synthesis strategy uses a layered compound, vanadiumÂ(III)
jarosite, as the precursor, in which the Mn<sup>2+</sup> ions are
doped uniformly between the vanadium oxide crystal layers. Through
a two-step transformation, the vanadium jarosite was converted into
Mn<sup>2+</sup>-doped V<sub>2</sub>O<sub>5</sub>. The resulting aliovalent
doping of the larger Mn cations in the modified V<sub>2</sub>O<sub>5</sub> structure increases the cell volume, which facilitates diffusion
of Li<sup>+</sup> ions, and introduces oxygen vacancies that improve
the electronic conductivity. Comparison of the electrochemical performance
in Li-ion batteries of undoped and the Mn<sup>2+</sup>-doped V<sub>2</sub>O<sub>5</sub> hierarchical structure made from layered vanadium
jarosite confirms that the Mn-doping improves ion transport to give
a high cathodic columbic capacity (253 mAhg<sup>–1</sup> at
1C, 86% of the theoretical value, 294 mAhg<sup>–1</sup>) and
excellent cycling stability