Insight into different-microstructured ZnO/graphene-functionalized separators affecting the performance of lithium–sulfur batteries

Abstract

A multifunctional separator composed of different dimensional ZnO and graphene is fabricated via a vacuum filtration method, which can provide sufficient active sites to adsorb polysulfides, thus enhancing the cycling stability and rate performance of lithium–sulfur batteries.

Improve redox activity and cycling stability of the lithium‐sulfur batteries via in situ formation of a sponge‐like separator modification layer

“…By changing the scan rate from 0.05 to 0.3 mV s −1 , the maximum current at both cathodic (C1 and C2) and anodic (A) peaks were recorded (Figure 2C‐E) and analyzed based on the Randles‐Sevick equation (Figure 2F‐H). The good consistence between the square root of the scan rate and fitting line indicates a Li + diffusion‐limiting process, which validates the applicability of the Randles‐Sevick theory . Interestingly, the calculated D Li+ values increased from 8.0 × 10 −8 (C1), 3.0 × 10 −8 (C2), and 6.8 × 10 −8 cm 2 s −1 (A) for the routine PE separator to 1.6 × 10 −7 (C1), 3.2 × 10 −8 (C2), and 7.6 × 10 −8 (A) for the KB/PE membrane, and 2.7 × 10 −7 (C1), 4.2 × 10 −8 (C2), and 1.4 × 10 −7 cm 2 s −1 (A) for the KB‐TPS/PE separator, which is consistent with the measured Li + conductance results (Figure 2B).…”

“…Typically, at 0.2C, the discharge capacities from the fifth to the 35th cycle were reduced by 75.1 mAh g −1 for the cell with PE separator, which probably due to the diffusion of the soluble polysulfides to the anode side through the root‐like membrane. As verified by the previous work, the polysulfide can undergo an irreversible electrochemical reaction with the metal Li, leading to the loss of the cathode active material. The cell with KB/PE separator, another control membrane, exhibits a 19.6 mAh g −1 decrease in discharge capacities, further confirming a degradation of performance recovery capability due to the shuttle effect of polysulfides.…”

“…As depicted in Figure 4A, two cathodic peaks and one overlapping anodic peak were observed for all the three samples. The cathodic peaks C1 and C2 can be ascribed to the reduction of cyclic sulfur S 8 to soluble polysulfide (ie, Li 2 S 4 ) and insoluble Li 2 S 2 /Li 2 S, respectively . Correspondingly, the anodic peak A represents the oxidation of Li 2 S 2 /Li 2 S to S 8 .…”

“…First, comparing with the battery with PE separator, the area of both cathodic and anodic peaks have been significantly increased when KB‐TPS functional layer was used, indicating an intense redox activity in the Li‐S battery. Secondly, voltage differences between the cathodic (C1) and anodic (A) peaks decreased from 0.53 V for the PE separator to 0.37 V for the KB‐TPS/PE membrane, suggesting a reduced polarization resistance of the cell with KB‐TPS functional layer . All these changes in electrochemical properties of the Li‐S batteries can be ascribed to the high electrical conductivity and ions (Li + ) transportation capacity of the KB‐TPS layer, which serves as an upper current collector and is beneficial to the charge transfer process associated with the redox reaction (Figure 2A,B).…”

“…The CV data were collected on a VMP2 multichannel electrochemical workstation at a scanning rate that increased from 0.05 to 0.3 mV s −1 . The D Li+ values of PE, KB/PE, and KB‐TPS/PE separators were obtained according to the Randles‐Sevick equation (Equation ) …”