1 after 200 and 300 cycles, respectively, with a CE of 99.3% (Fig. 5b and Supplementary Table 4). The capacity retention ratio of Co-PCL was 87.2% after 300 cycles, which is the highest among the tested cathodes. The rate capability of each M-PCL embedded

formance of pristine CNT and M-PCL embedded cathodes at 167.5 mA g−1 with an E/S ratio of 4.5 μL mg−1. b Cycling performance of Fe-PCL and Co-PCL embedded cathodes at 167.5 mA g−1 with an E/S ratio of 4.5 μL mg−1. c Rate capability of pristine CNT and M-PCL embedded cathodes. d Long-term cycling performance of the Co-PCL embedded cathode at 83.8 mA g−1 with an E/S ratio of 4.5 μL mg−1. The areal S loading and E/S ratio were fixed to 5.0 mg cm−2 and 4.5 μL mg−1, respectively.output: title: Construction of thin PCL on metal electrocatalysts

mA h g−1 at 200 and 300 cycles, respectively, with a capacity retention ratio of 87.1 and 74.6%. Fe-PCL showed a discharge capacity of 957 and 807 mA h g−1 at 200 and 300 cycles, respectively, with a capacity retention ratio of 91.0 and 76.7%. The CE of Fe-PCL and Co-PCL was maintained at ~100% during the initial 100 cycles and gradually decreased to ~99% at 200 cycles (Fig. 5c). The CE of Fe-PCL and Co-PCL was maintained at ~99% during the initial 100 cycles and gradually decreased to ~99% at 200 cycles (Fig. 5c). The voltage profiles of Fe-PCL and Co-PCL during the initial five cycles at 167.5 mA g−1 are shown in Fig. 5d. The voltage profiles of Fe-PCL and Co-PCL showed two voltage plateaus at ~2.3 and ~2.0 V during the discharge process, which correspond to the reduction of sulfur to soluble LiPS and the subsequent conversion of LiPS to solid-phase Li2S, respectively. During the charge process, two voltage plateaus at ~2.3 and ~2.5 V were observed, which correspond to the oxidation of solid-phase Li2S to LiPS and the subsequent oxidation of LiPS to sulfur, respectively. The voltage gap between the charge and discharge voltage profiles was 0.25 and 0.22 V for Fe-PCL and Co-PCL, respectively, which indicates the lower polarization of Co-PCL than that of Fe-PCL.

Coin-cell performance of pristine CNT, Ni-PCL, Fe-PCL, and Co-PCL. a Discharge capacity and b capacity retention ratio of pristine CNT, Ni-PCL, Fe-PCL, and Co-PCL at 167.5 mA g−1 with an E/S ratio of 4.5 μL mg-1. c Coulombic efficiency of pristine CNT, Ni-PCL, Fe-PCL, and Co-PCL at 167.5 mA g−1 with an E/S ratio of 4.5 μL mg-1. d Voltage profiles of Fe-PCL and Co-PCL during the initial five cycles at 167.5 mA g−1 with an E/S ratio of 4.5 μL mg-1.output