Delocalized Lithium Ion Flux by Solid-State Electrolyte Composites Coupled with 3D Porous Nanostructures for Highly Stable Lithium Metal Batteries

Abstract

This work investigates the root cause of failure with the ultimate anode, Li metal, when employing conventional/composite separators and/or porous anodes. Then a feasible route of utilizing Li metal is presented. Our operando and microscopy studies have unveiled that Li⁺ flux passing through the conventional separator is not uniform, resulting in preferential Li plating/stripping. Porous anodes alone are subject to clogging with moderate- or high-loading cathodes. Here we discovered it is necessary to seek synergy from our separator and anode pair to deliver delocalized Li⁺ to the anode and then uniformly plate Li metal over the large surface areas of the porous anode. Our polymer composite separator containing a solid-state electrolyte (SE) can provide numerous Li⁺ passages through the percolated SE and pore networks. Our finite element analysis and comparative tests disclosed the synergy between the homogeneous Li⁺ flux and current density reduction on the anode. Our composite separators have induced compact and uniform Li plating with robust inorganic-rich solid electrolyte interphase layers. The porous anode decreased the nucleation overpotential and interfacial contact impedance during Li plating. Full cell tests with LiFePO₄ and Li[Ni_0.8Mn_0.1Co_0.1]O₂ (NMC811) exhibited remarkable cycling behaviors: ～80% capacity retention at the 750th and 235th cycle, respectively. A high-loading NMC811 (4 mAh cm^–2) full cell displayed maximum cell-level energy densities of 334 Wh kg^–1 and 783 Wh L^–1. This work proposes a solution for raising energy density by adopting Li metal, which could be a viable option considering only incremental advancement in conventional cathodes lately.