Pre-Solid Electrolyte Interphase-Covered Li Metal Anode with Improved Electro-Chemo-Mechanical Reliability in High-Energy-Density Batteries

Abstract

Mossy/dendritic lithium growth and infinite volume change lead to form an unstable solid electrolyte interphase (SEI) on the Li surface, thus resulting in poor cyclability in Li metal-based batteries. Design of a reliable SEI layer on Li metal is one of the promising strategies to reach high-energy-density lithium-ion batteries. In this article, we report a novel design of artificial pre-SEI-covered Li metal by using a facile drop-coating process which advances a highly reliable SEI formation with uniform Li plating/stripping, enabling a greatly increased cycling performance with high Coulombic efficiency in full-cell batteries. The electron-isolated organic polymer matrix provides elastic deformation that decreases the fracture failure, thus avoiding the crack during cycling. The formed metal-organic-salt LiCN through the precursor reaction with Li metal suffices a robust connection. In parallel, the homogeneous distribution of inorganic compounds ensures an enhanced ionic conductivity, which leads to a thinner, stable SEI layer by reducing electrolyte consumption and forming less dead lithium. As a result, the full-cell battery versus LiNi_0.8Co_0.15Al_0.05O₂ displayed a high capacity of 167.8 mA h g^-1 after 100 cycles at 0.2 C in an electrolyte of 5.0 μL (mA h)^-1, while the battery with Li foil dropped to only 48.5 mA h g^-1 after 65 cycles. The estimated energy density of the coin cell battery was about 404.8 W h kg^-1 in the lean electrolyte of 1.25 μL (mA h)^-1. A high capacity retention over 84.0 and 81.0% and a Coulombic inefficiency less than 0.71 and 0.68% after 150 cycles with the 150 and 300 mA h pouch cell batteries paired with LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) were, respectively, achieved, which are much better than those of the batteries with Li foil. It is believed that the reinforced artificial pre-SEI covered on Li metal opens a new pathway to create a highly reliable, safe Li metal electrode for high energy-density batteries.

Keywords: Li metal anode; high-energy density; lithium-ion batteries; stable SEI; surface modification.