Constructing dendrite-suppressing separator based on cellulose acetate and polyoxometalates toward uniform lithium electrodeposition

Abstract

The functionalized separator is expected to serve as a protective barrier to conquer the lithium dendrite penetration in lithium metal batteries. Herein, a novel self-supporting separator material has been successfully synthesized based on the cellulose acetate and Keggin-type polyoxometalate H3PMo12O40xH2O (marked as CA/PMo12). The incorporation of PMo12 facilitates the transformation of the original finger-like structure of CA separator into a uniform three-dimensional porous grid architecture, which is more effective in inhibiting the growth of lithium dendrites. For the obtained CA/PMo12 separator, the mechanical strength, electrolyte uptake capacity, and Li+ anchoring ability have been significantly improved. The plentiful ether and carbonyl functional groups of CA can effectively adsorb lithium ions and regulate the uniform lithium plating. More significantly, density functional theory calculation shows that the coordination environment formed between PMo12 and CA is conducive to enhancing the adsorption ability of lithium ions and promoting the rapid migration of lithium ions. Meanwhile, PMo12 can act as an “ion sponge” to form a lithium-rich layer, making the distribution of charges on the lithium surface more uniform, while undergoing the reversible transformation between its reduced and oxidized states during repeated plating/stripping processes. Consequently, the Li//Li symmetrical cell using CA/PMo12 separator shows excellent plating/stripping efficiency after 1075 cycles with a low hysteresis voltage of 38.1 mV under 5 mA cm-2 and 1 mAh cm-2. Meanwhile, LiFePO4//Li cell achieves the superior reversible capacity of 90 mAh g-1 after 100 cycles under 1 C.