A MOF-derived hollow Co 3 O 4 /NiCo 2 O 4 nanohybrid: a novel anode for aqueous lithium ion batteries with high energy density and a wide electrochemical window.

Aqueous lithium-ion batteries (LIBs) have attracted increasing attention because of their higher safety and nontoxicity compared to traditional LIBs. However, crucial shortcomings impede their practical applications. A narrow electrochemical window restricts the capacity of aqueous LIBs so the ultrahigh concentration electrolyte lithium bistrifluoromethosulfonimide (LiTFSI) is introduced to widen the electrochemical window in this work. With the addition of LiTFSI, the electrochemical window of the created aqueous LIBs is improved to 2 V. Moreover, the material design promotes the high density of aqueous LIBs, in which hollow Co 3 O 4 nanocrystals obtained by the metal organic framework (MOF) template are connected with NiCo 2 O 4 nanorods to form three-dimensional nanohybrids. The formed Co 3 O 4 /NiCo 2 O 4 (CN) materials can provide NiCo 2 O 4 channels for electron transfer between hollow Co 3 O 4 which can offer more lithium-ions insertion. These effects work together synergistically to achieve aqueous LIBs with a wide electrochemical window and high energy density (93.07 W h kg -1 at 0.5 C). CN-6/LiMn 2 O 4 -based aqueous LIBs with LiTFSI as the electrolyte take into account both environmental friendliness and sustainable energy storage and exhibit great potential for producing novel clean energy storage devices from the concepts of material design and synthesis.