RESUMEN
The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A gS-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS-1) corresponding to an initial specific power of 26,120 W kgS-1 and specific energy of 1,306 Wh kgS-1.
RESUMEN
Seeking an electrochemical catalyst to accelerate the liquid-to-solid conversion of soluble lithium polysulfides to insoluble products is crucial to inhibit the shuttle effect in lithium-sulfur (Li-S) batteries and thus increase their practical energy density. Mn-based mullite (SmMn2 O5 ) is used as a model catalyst for the sulfur redox reaction to show how the design rules involving lattice matching and 3d-orbital selection improve catalyst performance. Theoretical simulation shows that the positions of Mn and O active sites on the (001) surface are a good match with those of Li and S atoms in polysulfides, resulting in their tight anchoring to each other. Fundamentally, dz2 and dx2 -y2 around the Fermi level are found to be crucial for strongly coupling with the p-orbitals of the polysulfides and thus decreasing the redox overpotential. Following the theoretical calculation, SmMn2 O5 catalyst is synthesized and used as an interlayer in a Li-S battery. The resulted battery has a high cycling stability over 1500 cycles at 0.5 C and more promisingly a high areal capacity of 7.5 mAh cm-2 is achieved with a sulfur loading of ≈5.6 mg cm-2 under the condition of a low electrolyte/sulfur (E/S) value ≈4.6 µL mg-1 .
RESUMEN
The shuttling of soluble lithium polysulfides between the electrodes leads to serious capacity fading and excess use of electrolyte, which severely bottlenecks practical use of Li-S batteries. Here, selective catalysis is proposed as a fundamental remedy for the consecutive solid-liquid-solid sulfur redox reactions. The proof-of-concept Indium (In)-based catalyst targetedly decelerates the solid-liquid conversion, dissolution of elemental sulfur to polysulfides, while accelerates the liquid-solid conversion, deposition of polysulfides into insoluble Li2 S, which basically reduces accumulation of polysulfides in electrolyte, finally inhibiting the shuttle effect. The selective catalysis is revealed, experimentally and theoretically, by changes of activation energies and kinetic currents, modified reaction pathway together with the probed dynamically changing catalyst (LiInS2 catalyst), and gradual deactivation of the In-based catalyst. The In-based battery works steadily over 1000 cycles at 4.0 C and yields an initial areal capacity up to 9.4 mAh cm-2 with a sulfur loading of ≈9.0 mg cm-2 .
RESUMEN
The shuttling of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries results in low sulfur utilization and fast capacity decay, hindering their practical applications. Constructing an interlayer is an efficient way to block the LiPS shuttling, but maintaining a low Li ion diffusion resistance with such an interlayer is hard to achieve. Herein, a thin porous carbon nanosheet embedded with TiO2 nanoparticles (denoted PCNS-TiO2) was used to fabricate an interlayer on the separator, which effectively solves the above problem. The PCNS-TiO2 was prepared by using the Ti3C2Tx MXene as the two-dimensional (2D) template directing the porous carbon sheet formation, and the Ti3C2Tx transformed into TiO2 nanoparticles embedded in the PCNS. The decomposition of the MXene eliminates the ion blocking effect by the 2D nanosheet structure. The thin and hierarchical porous structure allows fast Li ion diffusion across the interlayer, and at the same time, the porous structure and the strong adsorption ability of TiO2 effectively block the polysulfide diffusion. Thus, the Li-S battery with this interlayer shows good rate performance with a high capacity of 627 mA h g-1 at 2 C. Meanwhile, stable cycling performance is also achieved, showing a low capacity decay of 0.063% per cycle after 300 cycles at 0.5 C.
RESUMEN
Lithium-sulfur batteries suffer from poor cycling stability at high areal sulfur loadings (ASLs) mainly because of the infamous shuttle problem and the increasing diffusion distance for ions to diffuse along the vertical direction of the cathode plane. Here, a carbon nanotube (CNT)/graphene (Gra)-S-Al3Ni2 cathode with 3D network structure is designed and prepared. The 3D network configuration and the Al in the Al3Ni2 provide an efficient channel for fast electron and ion transfer in the three dimensions, especially along the vertical direction of the cathode. The introduction of Ni in the Al3Ni2 is able to suppress the shuttle effect via accelerating reaction kinetics of lithium polysulfide species conversion reactions. The CNT/Gra-S-Al3Ni2 cathode exhibits ultrahigh cycle-ability at 1 C over 800 cycles, with a capacity degradation rate of 0.055% per cycle. Additionally, having high ASLs of 3.3 mg cm-2, the electrode delivers a high reversible areal capacity of 2.05 mA h cm-2 (622 mA h g-1) over 200 cycles at a higher current density of 2.76 mA cm-2 with high capacity retention of 85.9%. The outstanding discharge performance indicates that the design offers a promising avenue to develop long-life cycle and high-sulfur-loading Li-S batteries.
RESUMEN
Lithium-sulfur batteries have become an appealing candidate for next-generation energy-storage technologies because of their low cost and high energy density. However, one of their major practical problems is the high solubility of long-chain lithium polysulfides and their infamous shuttle effect, which causes low Coulombic efficiency and sulfur loss. Here, we introduced a concept involving the dithiothreitol (DTT) assisted scission of polysulfides into lithium-sulfur system. Our designed porous carbon nanotube/S cathode coupling with a lightweight graphene/DTT interlayer (PCNTs-S@Gra/DTT) exhibited ultrahigh cycle-ability even at 5 C over 1100 cycles, with a capacity degradation rate of 0.036% per cycle. Additionally, the PCNTs-S@Gra/DTT electrode with a 3.51 mg cm-2 sulfur mass loading delivered a high initial areal capacity of 5.29 mAh cm-2 (1509 mAh g-1) at current density of 0.58 mA cm-2, and the reversible areal capacity of the cell was maintained at 3.45 mAh cm-2 (984 mAh g-1) over 200 cycles at a higher current density of 1.17 mA cm-2. Employing this molecule scission principle offers a promising avenue to achieve high-performance lithium-sulfur batteries.
