Solvent polarizability governs Li⁺ transport kinetics for high energy lithium metal batteries

Abstract

Fast Li+ kinetics are essential for high energy lithium metal batteries, yet the factors governing these kinetics remain unclear. Here, we decipher a quantitative structure-kinetics relationship by demonstrating that polarizability dictates Li+ desolvation and transport. Specifically, the inert solvents with low polarizability generate weak induced dipoles under interfacial electric fields, which keeps the structural integrity of anion-rich solvates. These intact solvates improve the Li+ kinetics via coupling Li+ hopping and electrostatic repulsion to anions, as evidenced by the linear relationship between polarizability and desolvation energy. Meanwhile, the induced more inorganic-rich solid-electrolyte interphase further accelerates the Li+ kinetics. Accordingly, the tailored electrolyte enables Li | |LiNi0.8Co0.1Mn0.1O2 cells to achieve a stable cycling (0.2 C charge/0.5 C discharge, 1 C = 200 mA g−1 based on the NCM811 positive electrode) with 95% capacity retention after 200 cycles at −35 °C and powers a 7.5-Ah lithium metal pouch cell (0.1 C charge/0.3 C discharge, 1 C = 200 mA g−1 based on the NCM811 positive electrode) with a specific energy of 541.6 Wh kg−1 (based on the full cell mass). This work decodes the polarizability-governed Li+ kinetics and establishes practical electrolyte guidelines for realizing high energy lithium metal batteries. Understanding factors that influence Li+ transport in liquid electrolytes is required for high-energy lithium metal batteries. Here, authors show that low polarizability solvents form anion-rich solvates, lower desolvation energy, and stable interphases enabling cycling at −35 °C, in Ah-scale pouch cells with 541.6 Wh kg-1 specific energy, and in initially anode-free pouch cells