Metal Organic Framework (MOF)-Derived carbon-encapsulated cuprous sulfide cathode based on displacement reaction for Hybrid Mg2+/Li+ batteries

We fabricate in-situ carbon-encapsulated cuprous sulfide (Cu 2 S@C) composite through a metal-organic framework (MOF)-derived sulfurization method and compare its electrochemical performance as a displacement reaction cathode of hybrid Mg 2+ /Li + batteries with 0.4 mol L −1 (PhMgCl) 2 -AlCl 3 +1.0 mol L −1 LiCl/THF nucleophilic hybrid electrolyte and 0.2 mol L −1  Mg(HMDS) 2 -(AlCl 3 ) 2 –MgCl 2 +1.0 mol L −1 LiTFSI/DME non-nucleophilic hybrid electrolyte. Benefiting from the intrinsic property of Cu 2 S, well-defined hybrid porous structure and carbon encapsulation derived from MOFs, the Cu 2 S@C composite exhibits 399.2 mA h g −1 discharge capacity and the capacity maintains at approximately 150 mA h g −1 at 0.05 C after 50 cycles in the nucleophilic hybrid electrolyte. The mechanism investigation verifies that the formed Cu 1.96 S in the first discharge process succeeds to transform into MgS and Li 2 S, which results in the reversible displacement reaction dominantly occurring between Cu 1.96 S and Cu during subsequent cycles. When using the non-nucleophilic hybrid electrolyte, an enhanced cycling stability can be achieved due to the mitigation of ionic sulfide dissolution. The present work demonstrates the feasibility of building the structural design of low-cost displacement reaction cathode with more compatible electrolyte, and provides the potential of establishing practical hybrid Mg 2+ /Li + batteries for energy storage.