Position difference between Mo clusters and N sites induced highly synergistic electrocatalysis in integrated electrode-separator membranes with crosslinked hierarchically porous interface

Herein, scalable integrated electrode-separator membranes with hierarchical porous interface are reported for promoting Li+/electrolyte transfer and Al-free refined Li-S battery configuration. The electrode side (CNT@Mo-NC) with ultrahigh porosity of 89% is composed with CNT as skeleton and Mo/N-codoped carbon (Mo-NC) as the crosslinked shell, the unique porous membrane electrode side and interface can strengthen transfer of Li+/electrons/electrolyte for fast reaction kinetics, and provide large space for polysulfide (LiPSs) anchoring and volume expansion. Furthermore, the N active sites with Li+-transfer transition function and Mo clusters with LiPSs adsorption and catalytic ability constitute a highly-efficient synergistic effect in mitigating shuttle effect and reducing energy barrier of redox reaction. For the Mo-13-NC-a surface with adjacent Mo and N, the LiPSs are adsorbed by Mo during the discharge process, and the N sites with lone electron pairs can accelerate diffusion of the positively charged Li+ to Mo, and to react quickly with LiPSs and transform into Li2S. For Mo-13-NC-b surface, however, the repulsion effect between Mo and Li+ during the charge process can promote the rapid migration of the dissociated Li+ to surround graphene due to the N center is occupied by Mo, which is beneficial to the dissociation reaction of Li2S. For the separator side (CNT@NP) with CNT as the skeleton and nonconductive polymer (NP) as crosslinked shell, the porous structure also facilitates the Li+/electrolyte transport. With uniform sulfur loading in the electrode side, an Al/Cu free Li-S battery with refined configuration and long-term cycle stability is formed. The proposed strategy has an important guiding significance for the design of membrane-based electrode/separator/interlayer with low ion/electrolyte transfer resistance in Li-S batteries.