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

Abstract

Functionalized separators are expected to serve as protective barriers 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 H₃PMo₁₂O₄₀·xH₂O (denoted as CA/PMo₁₂). The incorporation of PMo₁₂ facilitates the transformation of the original finger-like structure of the 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 are 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 calculations show 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 a reversible transformation between its reduced and oxidized states during repeated plating/stripping processes. Consequently, the Li//Li symmetric cell using a 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 mA h cm⁻². Meanwhile, a LiFePO₄//Li cell achieves a superior reversible capacity of 90 mA h g⁻¹ after 100 cycles under 1 C.