Lithium (Li) metal is an ideal candidate as the anode of Li batteries. However, Li metal anode is challenging to implement due to several drawbacks. First, Li easily reacts with electrolytes to form a solid electrolyte interface (SEI), whose heterogeneous nature results in local fluctuation of Li+ flux, leading to the formation of dendrites. Second, large volume change during Li stripping/plating creates cracks in the brittle SEI, forms dead Li, and causes electrolyte consumption. These effects lower the Coulombic efficiency (CE) and devastate the cycle life of Li metal anodes. Artificial SEI strategy is proposed to protect Li metal anode, which should have several key properties. First, high modulus coatings on Li was proposed to be beneficial while our recent work suggested flowability and dynamic property also allow SEI to adapt to large volume change during cycling, and result in uniform Li deposition macroscopically. Second, uniform and fast Li+ single-ion conduction in the artificial SEI is beneficial to increase critical Li deposit size, and stabilize the Li metal anode. Finally, the SEI needs to be both chemically and electrochemically inert itself and mitigate electrolyte penetration to minimize deleterious Li/coating and Li/electrolyte side reactions. Nevertheless, few artificial SEIs possess all the desirable properties such as dynamic adaptivity, high ion conductivity, and chemical passivation. Herein, we propose an artificial SEI design based on a dynamic polymeric network with high Li+ single-ion conductivity. In this network, tetrahedral Al(OR)4- (R = soft organic linker) anions are used for the first time as a dynamic motif while providing counter anions for Li+. The mechanical properties, ion transport pathway, and electrolyte-blocking feature were all characterized and cross-validated in detail. With this dynamic single-ion-conductive network (DSN) as an artificial SEI, we demonstrate over 400 stable plating/stripping cycles in Li||Cu cell using commercial carbonate electrolyte. Over 85% capacity retention for 160 cycles in a Li||NMC full battery was achieved using directly coated Li foils and commercial NMC cathode sheets.

Dynamic, electrolyte-blocking and single-ion-conductive network as the artificial solid electrolyte interphase to stabilize lithium metal anode

ACS Spring Meeting 2021

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