ZIF 67@Ce-MOF derived Co-N-C@CeO2-C for separator modification of lithium sulfur batteries

Abstract

High energy density Lithium-sulfur batteries (LSBs) have become one of the future energy storage devices. However, the shuttle effect induced by the diffusion of polysulfides between the positive and negative electrodes makes the application prospects of LSBs very challenging. So as to overcome this difficult challenge, a special Co-N-C@CeO2-C composite which displays the Co-N-C nanoparticle coated on CeO2-C nanorods structure was obtained using ZIF-67@Ce-MOF precursor, and applied as the separator modification material for LSBs. This Co-N-C@CeO2-C composite has a higher specific surface area and more micro/meso porous structures than the simple Ce-MOF derived CeO2-C nanorod. The presence of Co-N-C nanoparticles can induce the charge imbalance, resulting in more oxygen vacancy defects and plenty of active sites. By virtue of its excellent physical and chemical adsorption ability, the long chain polysulfide can be quickly bound to the surface of the material, furthermore the metal active centers are used to accelerate the transformation of polysulfides, effectively inhibiting its shuttle effect. Moreover, the combination of Co-N-C enhanced the conductivity of CeO2-C nanorod and the mobility of lithium ions. Therefore, when the sulfur content is 2.8 mg cm−1, the specific capacity of 915.9 mAh g−1 is released under 0.5 C, and there is still 46.63 % capacity retained after 700 cycles. Even under a high sulfur area density of 5 mg cm−1, an initial discharge capacity of 933.9 mAh g−1 can be achieved, furthermore it can maintain 72.75 % of the initial capacity at the 120th cycle, demonstrating its application value.