Revealing structure-performance relationship of biomimetic cyclodextrin metal-organic framework composite electrolytes for dendrite-free lithium metal batteries.

Cyclodextrin metal-organic frameworks (CD-MOFs) with infinitely extensible network structures show potential applications in lithium metal batteries. However, the disordered accumulation of CD-MOF particles leads to slow interparticle diffusion of ions, so the CD-MOF composite electrolytes are needed to be developed. In addition, the influences of CD-MOFs structure on the electrochemical performance of the composite electrolytes remains unclear. Herein, a series of CD-MOF composite electrolytes (BCDM-X) were prepared via in-situ growth of various CD-MOFs on bacterial cellulose (BC) fibers to research the structure-performance relationship of the CD-MOF composite electrolytes. The difference in host-guest interactions and the solvation structures of the BCDM-X were confirmed by FTIR, Raman spectroscopes and theoretical calculations. It is demonstrated that the BCDM-1 electrolyte with an open multilevel hierarchical pore structure and a moderate pore size 1 to 2 times the size of anion profits for ion-sieving and regulation of solvation structure as the beat one. Therefore, the BCDM-1 electrolyte achieves high lithium-ion transference number (0.82), good ionic conductivity (1.61 mS cm), wide electrochemical stability window (5.1 V), and stable long-term Li plating/stripping cycling over 1500 h at 0.2 mA cm. By realizing homogeneous Li flux, the BCDM-1 composite electrolyte can inhibit the growth of lithium dendrites on the Li metal anode, prevent electrolyte decomposition, and facilitate the formation of a durable LiF-rich SEI layer. Thus, this work provides understanding of the structure-performance relationship of CD-MOF composite electrolytes for dendrite-free and high-performance LMBs.